Exploring the Potential of Actinobacteria as Plant Growth Promoters in Cowpea

Exploring the Potential of Actinobacteria as Plant Growth Promoters in Cowpea | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Exploring the Potential of Actinobacteria as Plant Growth Promoters in Cowpea Niveditha Nelamangala Lalithesh, Girija Devaki, Kulkarni Surendra Gopal, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5368610/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The study includes isolation, characterization and evaluation of actinobacteria for plant growth promotion in cowpea. Actinobacteria were isolated from four soil and three compost samples on starch casein agar and total 50 morphotypes were maintained including 21 isolates from the Department of Agricultural Microbiology repository. All 50 isolates were subjected to screening for direct plant growth promoting (PGP) activities including nitrogen fixation, phosphate, potassium and zinc solubilization and production of indole-3-acetic acid. Indirect PGP activities including production of hydrogen cyanide, ammonia and siderophores were also tested under in vitro conditions. Compatibility among isolates was tested via cross-streak method and five actinobacterial consortia were developed for further in planta studies. A total of 29 actinobacterial isolates were obtained from rhizosphere soil and compost samples, with cowpea rhizosphere soil exhibiting the highest population density. Based on in vitro screening and PGP ranking of all the 50 isolates, 15 isolates with PGP ability were selected for further cultural, biochemical and morphological characterization. The evaluation of five compatible consortia led to significant improvement in growth and yield parameters of cowpea compared to treatment of PGPR Mix 1 and control ( P ≤ 0.05). T 2 consortium ( Streptomyces fumigatiscleroticus and Streptomyces sp. strain PAS3) recorded significantly higher number of pods (23.8), number of seeds per pod (12.1), test weight (22.8 g), fresh (120.2 g) and dry weight (15.6 g) of pods, indicating their potential benefits for plant growth and yield. This research suggested actinobacterial consortia as viable biofertilizers, enhancing cowpea growth and contributing to environmentally sustainable agriculture. plant growth promotion actinobacteria cowpea consortia compost. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Cowpea ( Vigna ungiculata L.) known as the black-eyed pea or southern pea is a member of Leguminosae family is an annual grain legume native from Africa, cultivated as main crop and also as an intercrop in India. It is a protein-rich crop that complements staple cereal for human and fodder for livestock and also provides soil improvement benefits through nitrogen fixation. Despite being an important pulse crop, its productivity has been quite low due to various biotic and abiotic constraints. This global crop encounters a number of operational constraints, including pests and diseases that limit its production and yield potentials from seedling to harvest (Asiwe 2006). To address these challenges, sustainable and eco-friendly approaches are being explored. One promising strategy involves harnessing the plant growth-promoting (PGP) potential of actinobacteria. The indiscriminate use of chemical inputs has been linked to detrimental consequences for human and environmental health (Glick, 2012). The introduction of chemical inputs can have lasting impacts on plant evolution by altering the symbiotic relationships between plants and their microbiota, potentially influencing the co-evolution of the holobiont (Rosenberg et al . 2009) and compromising plant resilience. Therefore, there is an indispensable need for sustainable alternatives, particularly through the application of beneficial microorganisms. Many plant growth-promoting bacteria are readily available in the market, but actinobacteria have limited commercial application. The role of actinobacteria in crop improvement assures a promising future in the field of plant growth promotion and disease management in various crops. The application of actinobacteria in agriculture has increased, due to their ability to promote plant growth and interact beneficially with plant rhizospheres (Yadav et al . 2018). Actinobacteria are a group of Gram-positive bacteria, terrestrial or aquatic, having high guanine and cytosine content in their DNA. Most of the actinobacteria are saprophytes, ubiquitous and are one of the most diverse groups of bacteria in nature. Their nature varies from anaerobic unicellular organisms to aerobic, filamentous and spore forming lineages (Lewin et al . 2016). The morphology of actinobacteria varies from unicellular forms to complex filamentous forms, resembling fungi. Some actinobacteria produce spores by asexual reproduction. Hence many scientists hypothesize that they represent a transitional state between bacteria and fungi. Actinobacteria are among the plant growth promoting rhizobacteria (PGPR) equipped with multifunctional PGP traits and many properties beneficial to plant growth (El-Tarabily and Alkhajeh, 2019). These beneficial bacteria can stimulate plant growth under abiotic and biotic stress conditions via mechanisms such as the production of phytohormones, siderophores, ACC (1-aminocyclopropane-1-carboxylate) deaminase, exopolysaccharides, organic acids, nitrogen fixation, phosphate solubilization, various osmolytes, systemic resistance induction, etc (Khoshmanzar et al . 2020). Actinobacteria have been widely recognized for their plant growth-promoting (PGP) potential in crops such as tomato, wheat, rice, bean, chickpea, and pea. Passari et al . (2015) highlighted the potential of Streptomyces sp. (BPSAC34) as plant growth-promoting agent. Greenhouse experiments demonstrated the efficacy of these strains in stimulating growth and development of chilli ( Capsicum annuum L.), with notable improvements in key growth parameters. Hu et al . (2020) demonstrated the efficacy of Streptomyces sp. TOR3209 in promoting tomato growth and yield. Similarly, Vo et al . (2021) reported that four actinobacterial strains ( Microbispora sp. CP56, Actinomadura sp. CP84B, and Streptomyces spp. CP200B and CP21A) significantly improved chickpea growth and nodulation. Researchers at International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) have isolated and characterized PGP actinobacteria from herbal vermicomposts, demonstrating their in vitro PGP properties (Srinivas et al . 2021). Further investigations under controlled greenhouse and field conditions validated their effectiveness in enhancing growth and productivity in rice, sorghum, chickpea, and pigeon pea. Our study focused on isolation, screening, and characterization of actinobacteria from soil and compost samples to elucidate their potential as plant growth promoters in cowpea. Material and methods Isolation of actinobacteria from soil and compost samples Samples were collected from seven different sources including cowpea rhizosphere soil (CR) from Thrissur district, ginger rhizosphere soils (S) from Wayanad district, mangrove forest soil (MS) from Kadappuram (Chettuva) of Thrissur district, uncultivated soil (US) from Kerala Agricultural University (KAU) campus, Vellanikkara, Thrissur, compost (C), coir pith compost (Cc) and vermicompost (VC) from Thrissur district. Actinobacteria were isolated and enumerated from various samples using serial dilution and plating method (Johnson and Curl, 1972) on starch casein agar (HiMedia Laboratories, Mumbai, India). The Petri plates were incubated at 28 ± 2 o C for a period of five to 12 days. Pure cultures of a total of 50 morphotypes were maintained, including isolates from the repository at the Department of Agricultural Microbiology, KAU, Vellanikkara for further studies. In vitro screening of actinobacteria for plant growth promoting (PGP) activities All the 50 actinobacterial isolates were subjected to primary and secondary screening for various direct plant growth promoting activities including production of indole-3-acetic acid (IAA), nitrogen fixation, solubilisation of phosphate, potassium and zinc, and also indirect PGP activities such as production of hydrogen cyanide (HCN), ammonia and siderophores under in vitro conditions. Primary (qualitative) screening identified actinobacterial isolates with desired activities, whereas secondary (quantitative) screening measured the extent of these activities by measuring the concentration of the mineral solubilized and IAA produced. Primary and secondary screening of actinobacterial isolates for direct PGP activities IAA production Actinobacterial isolates were screened for the production of IAA (Ahmad et al . 2008). The pink colour development in Luria-Bertani (LB) broth indicated positive reaction for IAA production and it was measured for optical density (OD) at 530 nm using a spectrophotometer. The OD values were plotted on a standard graph to obtain the quantity of IAA produced by the isolates and expressed as mg ml − 1 of broth. Nitrogen fixation Fifty actinobacterial isolates were streaked onto N-free Jensen's agar medium, and the plates were incubated at 28 ± 2°C for six days. Isolates that exhibited growth on the nitrogen-free medium were classified as nitrogen fixers. Their ability to grow was observed and rated as follows: excellent (++++), good (+++), moderate (++), poor (+), and no growth (-). Further, Nitrogen fixation by the selected isolates was quantified by micro-Kjeldahl method (Jackson, 1973 and Bremner, 1960). Phosphate solubilization All the fifty actinobacterial isolates were screened for phosphate solubilization on Pikovskaya’s agar (Nguyen et al . 1992). Isolates exhibiting potential phosphate solubilization ability in preliminary screening were further assessed for quantitative phosphate solubilization using the phospho-molybdic blue colorimetric method (Olsen et al . 1962). Potassium solubilisation The fifty isolates obtained were screened for K solubilization on Aleksandrov’s agar (Nguyen et al . 1992). The quantity of potassium by the potential actinobacteria was determined by flame photometry (Sugumaran and Janarthanam, 2007). Zinc solubilisation The fifty isolates were evaluated for their ability to solubilize zinc on Tris minimal salt agar amended with 0.1% of insoluble zinc oxide (Saravanan et al . 2004). Screening of actinobacterial isolates for indirect PGP activities HCN production Hydrogen cyanide production was estimated using Luria-Bertani (LB) agar supplemented with glycine (4.4 g glycine/L) as per the method described by Lorck (1948). Petri plates were sealed with parafilm and incubated for 7 to 12 days at 28 ± 2 o C. After incubation, development of reddish-brown color on the filter paper indicated positive for HCN production. Siderophore production All actinobacterial isolates were assessed for siderophore production on Chrome Azurol Sulfonate (CAS) agar medium (Schwyn and Neilands, 1987). After seven days of incubation, colonies that produced yellow to orange halos were positive for siderophore production. Ammonia production Freshly grown actinobacterial isolates were inoculated to a sterilized 4% peptone water and incubated at 28 ± 2 o C for three to four days. After incubation, 0.5 ml of Nessler’s reagent was added to each tube. The development of orange to the brown colour indicated ammonia production (Cappucino et al . 1992). Selection of potential actinobacteria for further characterization Promising isolates for plant growth promotion were selected based on ranking of PGP traits (Backer, 2021). Isolates of actinobacteria were arranged on the basis of their IAA production, in decreasing order. A score of 10 was allotted to each of the PGP traits and sum of the scores were considered for ranking of the isolates. Isolates having highest ranking were selected and were subjected to further characterization. Characterization of the selected potential isolates Morphological and cultural characterization The selected actinobacteria were grown on starch casein agar media at 28 o C for seven days and characterized by observing colony appearance and the types of aerial hyphae. The color of spore masses and the production of pigments were also assessed. Gram staining was performed using the method outlined by Hucker and Conn (1923). Gram reaction and spore chain morphology were observed under the compound microscope of 100x magnification. Biochemical characterization Oxidase test The isolates were smeared on oxidase disc (Hi-media DD018-1VL). Appearance of violet colour within 5–10 seconds at 25-30 o C indicated positive reaction. A colour change after 60 seconds or no colour change considered as negative. Catalase test Smear of the isolates prepared in a clean glass slides and a drop of hydrogen peroxide (3%) was added. Cultures that immediately showed effervescence were treated as positive. (Taylor and Achanzar, 1972). Utilization of sugars Fermentation broth (containing glucose, sucrose and mannitol) was prepared in test tubes. Durham’s tubes were placed in an inverted position in the broth. The isolates were inoculated in broth and uninoculated control was also maintained. Three replications were maintained and incubated for 37 o C for 5 days. A change in colour from red to yellow and appearance of bubbles indicated positive for fermentation tests (Cowan, 1974). Molecular characterization The identification of the best performing consortia in pot culture evaluation was carried out by 16s rRNA gene sequencing. Genomic DNA was isolated using Nucleospin® Tissue Kit (Macherey-Nagel). Evaluation of quality of isolated DNA was carried out by agarose gel electrophoresis (Sambrook et al . 1989). After the separation of DNA bands using electrophoresis, the gels were visualized in a UV transilluminator and the image was taken under UV light using gel documentation system. The PCR product was then purified and sequenced at Rajiv Gandhi Centre for Biotechnology, Trivandrum using the primer 16S-RS-F and 16S-RS-R. The sequencing reaction of the PCR product was done in a PCR thermal cycler (GeneAmp PCR System 9700, Applied Biosystems) using the BigDye Terminator v3.1 Cycle Sequencing kit (Applied Biosystems, USA). The sequence quality was checked using Sequence Scanner Software v1 (Applied Biosystems). Sequence alignment and required editing of the obtained sequences were carried out using Geneious Pro v5.1 (Drummond et al . 2010). Sequence analysis and nucleotide homology of each isolates were identified through the BLASTn (basic local alignment search tool) programme of NCBI (National Centre for Biotechnology Information) ( http://www.ncbi.nlm.nih.gov ). The accession sharing maximum homology with the query sequence was used to identify the isolates. Compatibility of potential actinobacterial isolates with plant growth-promoting (PGP) activities The compatibility of the promising actinobacterial isolates was assessed using the in vitro cross-streak method. One actinobacterial isolate was streaked as a line on a starch-casein agar plate, while another test isolate was streaked perpendicularly to the first. The plates were incubated at 30°C for three days, and the growth of actinobacteria at the intersection was examined. A merger of the actinobacterial growth at this junction indicated compatibility, whereas inhibition zone indicated non-compatibility among the isolates (Al-Hussini et al . 2019). Preparation of talc based actinobacterial consortia Most efficient and promising isolates were selected for the preparation of talc based consortia. Talc was sterilized at 121°C and 15 psi for two hours, then mixed with compatible two or three actinobacterial cultures at a concentration of 10 8 CFU ml − 1 in a 1:2.5 ratio. In planta evaluation of actinobacterial consortia for growth promotion in cowpea The five actinobacterial consortia were assessed under sterile conditions for their efficacy in growth promotion of cowpea. The experiment was carried out from June to August 2024, using completely randomized design (CRD), The experiment consisted of seven treatments with three replicates, and each replicate had three pots. The first five treatments comprised the selected consortia, whereas the sixth and seventh treatments included PGPR Mix 1 from KAU and an uninoculated control, respectively. Sterile potting mixture was used for the experiment. Seeds of Bhagyalakshmy variety were treated with the KAU culture of Rhizobium sp. (strain Rh4), with three to four seeds sown in each pot. The soil was inoculated with the talc based actinobacterial consortia twice, initially one week after sowing and again one month after the first application. The population of actinobacteria in the potting mixture was evaluated at 30, 60 and 90 days after sowing (DAS). Observations on biometric parameters such as plant height, number of leaves, number of branches, days to flowering, number of effective nodules per plant were recorded at monthly intervals for three months after sowing. Fresh and dry weight of shoots, root parameters like fresh and dry weight of roots and root volume were recorded at 90 DAS. Yield parameters such as number of pods per plant, number of seeds per pod, test weight, fresh and dry weight of pods were observed after 90 DAS. Initial and final nutrient (N, P and K in kg ha − 1 ) profile of the potting mixture and nutrient status of plants after the experiment were recorded. Statistical analysis Analysis of variance (ANOVA) suitable to CRD was performed on the collected data using GRAPES version 1.0.0 (Gopinath et al . 2021) statistical software. Results and discussion Isolation of actinobacteria Modern agriculture needs sustainable practices to increase crop yields, boost production, and enhance soil fertility (Yasari et al . 2009). Actinobacteria can function as bio-inoculants and biopesticides, serving as an eco-friendly alternative to chemical fertilizers, by aiding crops in tolerating stress factors such as temperature, pH, salinity, and drought. (Cheng et al . 2018). These findings encouraged us to take up the present study which focuses on isolation, screening, and characterization of actinobacteria from rhizosphere soil, uncultivated soil, mangrove forest soil and compost samples to assess their potential as promoters of plant growth in cowpea. Among the various soil and compost samples analysed, cowpea rhizosphere soil (CR) recorded significantly superior actinobacterial population on starch casein agar, with a population of 42.9 x 10 6 cfu g -1 . Coirpith compost (Cc) recorded the population of 19.0 x 10 6 cfu g -1 . The lowest population was recorded in mangrove forest soil (MS) and ginger rhizosphere soil (S) with a population of 1.1x10 6 cfu g -1 and 1.2x10 6 cfu g -1 . In contrast, coir pith compost and ginger rhizosphere soil reported a significantly higher number of morphotypes (7), while mangrove forest soil recorded lowest number of morphotypes (1). Numerous studies support the findings of this research. Khamna et al . (2010) isolated 270 Streptomyces spp. from the rhizosphere soils of 14 Thai medicinal plants. Gopalakrishnan et al . (2012) reported that actinobacterial isolates obtained from herbal vermicompost can be employed for the biological control of Fusarium wilt of chickpea. Sreevidya et al . (2016) isolated and characterized actinobacteria with plant growth-promotion, from the rhizosphere of chickpea. Actinobacteria are susceptible to low pH (ideal pH range: 6.5-8.0) and acidity, as well as wet conditions. These are mesophilic organisms that thrive at 25-30˚C, whereas some species that are frequently found in compost and manures are thermophilic and grow at 55-65˚C (e.g. Thermoactinomycetes , Streptomyces ) (Bhatti et al . 2017). Meanwhile, Wolińska et al . (2019) reported that greater abundance of actinobacteria was observed in non-cultivated soils relative to the cultivated soils. Moreover, it was indicated that the actinobacterial diversity depended on both the soil genesis and the land use; however, this effect directly depended on the particular family and genera. Redox potential (Eh) and total carbon (TC) both seemed to significantly impact the diversity of actinobacteria. Nalini et al . (2020) reported that among the 40 actinobacterial isolates isolated from the different rhizosphere soil samples of legume crop, cowpea was rich in the actinobacteria population and starch casein agar proved to be the best medium for their enumeration. Law et al . (2023) reported a novel strain, Streptomyces griseiviridis MUM 136J T from a mangrove forest soil in Malaysia. Recently, Uesugi et al . (2024) isolated and characterized actinobacteria from industrial composting soil of oil palm ( Elaeis guineensis ) in the municipality of Igarapé-Açu, Pará. In vitro screening of actinobacterial isolates for plant growth promoting (PGP) traits Actinobacteria are known for synthesizing large amounts of phytohormones that enhance plant growth. Additionally, they play a crucial role in mobilizing nutrients like phosphate, zinc, and potassium in soils deficient in these micronutrients, thus significantly contributing to plant growth promotion (Mitra et al . 2022). As PGPR, actinobacteria utilize both direct and indirect mechanisms to enhance plant growth. Therefore, they can be regarded as plant biofertilizers (Franco-Correa and Chavarro-Anzola, 2016). In vitro primary and secondary screening for direct PGP activities revealed that among 50 isolates, only nine produced IAA with amount ranging between 11.3 and 90.9 mg ml -1 . The isolate ACT-3 (90.9 mg ml -1) was found to be significantly superior to all other isolates. There are many reports which demonstrated the ability of actinobacteria to produce IAA and thus promote plant growth (Solans et al . 2011; Dochhil et al . 2013). Suksaaid et al . (2017) reported that 51% of the mangrove actinobacterial isolates produced IAA in the range of 0.2 mg ml -1 to 165.7 mg ml -1 . Fourty eight isolates were predicted to fix atmospheric nitrogen where 15 isolates were strong nitrogen fixers. Four isolates viz. DPS-7, MS-3(1) , Cc-4 and CR-3 recorded significantly superior nitrogen fixation (Table 1). There are numerous evidences of actinobacteria involved in nitrogen fixation. The genus Frankia are widespread endophytic actinobacteria symbiotically associated with plant roots and fix atmospheric nitrogen for host plants (Benson and Silvester, 1993). In agriculture, biological phosphate solubilization serves as an important alternative to the use of natural phosphates, enhancing nutrient uptake efficiency. In this study, fifteen isolates exhibited phosphate solubilization, while potassium solubilization was observed in two isolates (US3 and VC5). These results are supported by many studies, Anwar et al . (2016), screened actinobacterial isolates for their phosphate solubilizing abilities and revealed that Streptomyces sp. WA-1 produced the highest soluble phosphate concentration (72.1 mg/100 ml), followed by S. djakartensis TB-4 (70.3 mg/100 ml). Etesami et al . (2017) reported that only 5% of potassium solubilizing bacteria available are actinobacteria. Archana (2007) isolated 30 potassium-solubilizing bacterial strains from soils in the Belgaum and Dharwad districts of Karnataka, using mica as an insoluble potassium source and potassium solubilization by the actinobacterial isolates varied from 2.4 to 44.4 μg ml⁻¹. In our study, none of the isolates showed the ability for zinc solubilisation on Tris minimal salt agar medium supplemented with 0.1% insoluble zinc oxide under in vitro conditions. However, Patel and Thakker (2020) found that Streptomyces nanhaiensis strain YM4 was capable of solubilizing zinc, with a concentration of 41.16 ppm. Microorganisms promote plant growth indirectly by producing compounds, such as siderophores, ammonia, HCN, and hydrolytic enzymes, which inhibit plant pathogens and reduce disease (Hayat et al . 2010). In our study, development of an orange to brown colour in 12 actinobacterial isolates (CS-4, CS-1, CS-6, WA-7, C2, S4-5, VC-5, DPS-5, CR-3, VC-4, CT-3, and DPS-6) following the addition of Nessler's reagent indicated the production of ammonia. Kaur et al . (2013) made similar observations, by detecting ammonia production in 12 out of 62 actinobacterial isolates. The production of siderophores by various soil actinobacteria retains iron in the soil environment and makes it available to the plants (Nimaichand et al . 2016). In addition, 9 isolates (US-3, US-4, C1, S2(2), WA-26, WA-22, CS-6(2), S4-2 and VC-5) produced siderophores but none of the isolates produced HCN. Sreevidya et al . (2016) isolated 89 actinobacteria and found that four Streptomyces strains produced significant quantities of siderophores, which improved plant growth and yield in field trials. Hydrogen cyanide has also been reported to play an important role in mineral mobilization and phosphate release, indirectly enhancing nutrient availability for both actinobacteria and their host plants (Rijavec and Lapanje, 2016) Table 1 Ranking of actinobacterial isolates based on IAA production, N fixation and solubilisation of phosphate and potassium Isolates IAA production (µg ml -1 ) Amount of nitrogen fixed (mg of N g -1 of C utilised) Quantity of P solubilized (µg ml -1 ) Quantity of K solubilized (µg ml -1 ) Total score Ranking Act-3 90.90 a - - - 909.0 16 Cc5 53.83 b - 91.87 f - 1457.0 1 US3 28.08 c - 93.09 d 3.86 a 1250.3 2 VC5 25.50 d - - 3.53 b 290.3 18 CR5 17.66 e - - - 176.6 19 C1 16.68 f - - - 166.8 20 VC4 15.63 g - - - 156.3 21 WA-25 14.47 h - - - 144.7 24 EK9K1 11.30 i - 94.25 b - 1055.5 5 Cs-1 - - 92.12 - 921.2 12 Cc1 - - 95.10 a - 951.0 9 WA-9 - - 89.55 k - 895.5 17 C2 - - 91.87 f - 918.7 13 Cs-10 - - 91.16 i - 911.6 15 WA-30 - - 91.41 h - 914.1 14 Cc4 - 15.38 a 92.12 e - 1075.0 3 DPS-7 - 15.42 a 91.88 f - 934.2 11 WA-27 - 2.56 e 91.16 i - 942.2 10 Cc2 - 5.13 d 90.67 j - 958.0 8 Cc6 - 12.84 b 93.88 c - 1067.2 4 WA-26 - 5.13 d 90.80 j - 959.3 7 DPS-5 - 12.84 b 91.64 g - 1044.8 6 MS-3(1) - 15.39 a - - 153.9 22 S3-2 - 5.13 d - - 51.3 27 CR3 - 15.36 a - - 153.6 23 WA-22 - 5.14 d - - 51.4 26 S3-1 - 2.57 e - - 25.7 30 S4-2 - 5.13 d - - 51.3 28 S1-3 - 10.24 e - - 102.4 25 Cc3 - 5.13 d - - 51.3 29 * Treatments with same letters are not significantly different Selection of efficient PGP actinobacteria for further characterization and in planta evaluation The isolates with first 15 ranks (US3, Cc4, Cc6, EK9K1, DPS-5, WA-26, Cc2, Cc1, WA-27, DPS-7, CS-1, Cc5, WA-30, CS-10, and ACT-3) were selected as the most efficient ones after ranking the isolates and were used for further characterization of actinobacteria followed by in planta evaluation. Characterization of actinobacterial isolates Actinobacterial isolates were characterized morphologically using Gram staining, which confirmed that they were Gram-positive and exhibited a filamentous structure. Cultural and morphological characteristics of actinobacteria are given in Table 2 and Fig. 2. Li et al . (2016) reported that actinobacteria produce two type of pigments water-soluble or diffusible pigment and fat-soluble or non-diffusible pigment. In our study, diffusible pigment production was observed in Cc1 and Cc6 (Fig. 3) and non-diffusible pigments were not reported. However, Thampi and Bhai (2017) stated that colony morphology is influenced by the type of media used, and therefore, cannot be considered a fundamental criterion for identifying microbes. Biochemical characterization of the isolates are presented in Table 3. In a similar study, Vyawahare et al . (2013) found that nine Streptomyces strains tested positive for both catalase and oxidase activity. Table 2 Morphological and cultural characterization of isolates Isolates Colony colour Elevation Form Margin Gram staining Pigment produced Cc1 Light brown Raised Circular Entire + Yellow (diffusible) Cc2 Grey Flat Circular Filiform + - Cc4 Creamish white Raised Circular Entire + - Cc5 Grey Umbonate Circular Entire + - Cc6 Off white Umbonate Circular Entire + Light yellow (diffusible) US3 Creamish white Umbonate Circular Curled + - WA-26 White Umbonate Irregular Curled + - DPS-7 Grey Raised Irregular Crateriform + - CS-1 Creamish white Umbonate Circular Filiform + - EK9K1 Whitish ash Convex Circular Filiform + - CS-10 Grey Raised Circular Entire + - WA-30 Off white Slightly raised Circular Entire + - DPS-5 White Umbonate Concentric ring Entire + - WA-27 Grey Umbonate Circular Filiform + - Act-3 Blackish brown Circular Convex Curled + - Table 3 Characterization of isolates based on biochemical tests Isolates Catalase Oxidase Utilization of sugars Glucose Sucrose Mannitol Cc2 + + - - - Cc4 + - - - - Cc5 + + - - - Cc6 + - - - + DPS-5 + - - - - DPS-7 + + - - - WA-26 + + - - - WA-27 + + - - - EK9K1 + - - - - CS-1 + - - - - CS-10 - - - - - WA-30 - + - - - WA-9 + + - - - Cc1 + - - - - US3 + - - + - ACT-3 - - - - - Compatibility of potential actinobacteria with PGP activities To develop the consortia formulation of PGP actinobacteria, compatibility among 15 selected isolates was tested by using cross streak method. All possible combinations of nine promising isolates were tested and the results revealed that among 15 isolates, only eight were showing compatibility. From this, five best combination of two isolates (Cc-5 and Cc-6; DPS-7 and Cc-5; DPS-7 and Cc-4; DPS-5 + WA-26; WA-27 and Cc-2) were selected for the preparation of talc-based consortia for further in planta evaluation. In planta evaluation of selected actinobacterial consortia for growth promotion in cowpea A pot culture experiment was conducted to evaluate the effect of five actinobacterial consortia in enchancing cowpea growth and yield. The abundance of actinobacterial population in the rhizosphere of cowpea at different intervals is given in the figure1. The population of actinobacteria ranged from 1.1 x10 6 cfu g -1 to 6.0 x10 6 cfu g -1 and T 2 and T 5 were statistically significant at all the intervals. No actinobacteria could be detected in the treatments T 6 (PGPR Mix 1 of KAU) and T 7 (uninoculated control) at 30, 60 and 90 DAS. Table 4 Population of actinobacteria in the rhizosphere of cowpea at various intervals (x10 6 cfu g -1 ) Treatments 30 DAS 60 DAS 90 DAS T 1 5.7 a (0.755 a ) 4.4 b (0.650 b ) 4.1 a (0.6127 a ) T 2 6.0 a (0.781 a ) 5.6 a (0.748 a ) 4.2 a (0.630 a ) T 3 4.3 b (0.633 b ) 3.7 c (0.568 c ) 3.1 b (0.501 b ) T 4 3.6 b (0.562 b ) 3.4 c (0.534 c ) 2.1 bc (0.439 bc ) T 5 5.7 a (0.757 a ) 5.2 c (0.722 c ) 2.5 c (0.397 c ) T 6 0 c 0 d 0 d T 7 0 c 0 d 0 d LSD (0.05) 1.14 0.735 0.426 Log transformed values are given in parentheses. Means followed by common letter(s) do not significantly differ. Actinobacterial inoculation significantly improved all the growth and yield parameters compared to the control treatment ( P ≤ 0.05). At 90 DAS, significantly higher plant height was observed in T 1 , T 2 , T 3 , and T 4 . Number of leaves per plant was significantly higher in T 1 , T 2 , and T 3 , while T 2 had the most branches. T 2 and T 3 recorded significantly higher fresh shoot weight. T 1 , T 2 , T 3 , and T 4 recorded higher fresh root weight, whileT 2 and T 3 recorded significantly higher dry root weight. Significantly higher root volume was observed in T 1 , T 2 , and T 6 . Time taken for flowering varied significantly among treatments. Earliest flowering (43.7 days) was noticed in T 1 , whereas it was longest in T 3 (46.5 days). At 60 DAS, T 1 recorded maximum number of nodules (37.9), followed by T 2 (31.7) and T 3 (28.2) (Fig. 4). Meanwhile, yield parameters such as number of pods (23.8), number of seeds per pod (12.1), test weight (22.8 g), fresh and dry weight of pods (120.2 g and 15.6 g) were also superior in T 2 , indicating their potential benefits for plant growth and yield (Fig. 5). Nutrient analysis of the plant samples also revealed that T2 recorded the highest N, P and K content of 55.43, 124.8 and 74.4 Kg ha- 1 respectively (Table 4). Post-experimental soil analysis revealed a significant increase in available phosphorus content in the potting mixture. Table 5 Effect of actinobacterial isolates on final nutrient status of plants under pot culture Treatments Nitrogen (kg ha -1 ) Phosphorus (kg ha -1 ) Potassium (kg ha -1 ) T 1 : Consortium 1 (DPS-7 + Cc-5) 41.65 d 98.88 bcd 59.87 bc T2: Consortium 2 (WA-27 + Cc-2) 55.43 a 124.84 a 74.44 a T 3 : Consortium 3 (Cc-5 + Cc-6) 49.74 b 109.39 ab 63.09 b T 4 : Consortium 4 (WA-26 + DPS-5) 45.78 c 83.30 d 54.68 bc T 5 : Consortium 5 (Cc-4 + DPS-7) 45.71 c 91.40 ad 60.59 bc T 6 : PGPR Mix 1 of KAU 46.04 c 104.23 bc 51.08 c T7: Control (uninoculated) 43.23 cd 91.82 cd 52.78 c This finding supports the results of several earlier studies. A study employing the "ragdoll" method investigated the impact of four Streptomyces spp. on chickpea seedling growth, revealed VAI-7 as the most effective strain in enhancing shoot and root lengths. Under field conditions, the Streptomyces spp. increased nodule number over un-inoculated control demonstrating a direct proof for enhancing nitrogen fixation. The Streptomyces strains used in the study exhibited increase in agronomic properties such as the shoot weight, leaf weight, leaf area, plant height, grain yield and stover yield over the un-inoculated control (Sreevidya et al . 2016). Previously it was reported that the culture filtrates of Streptomyces olivaceoviridis containing IAA stimulated growth and yield of wheat plants (Aldesuquy et al . 1998) and Streptomyces spp. from a tomato rhizosphere had the ability to produce IAA and improve tomato growth by increasing root dry weight (El-Tarabily, 2008). Htwe et al . (2019) observed that inoculation with Streptomyces griseoflavus enhanced agronomic traits, nodulation, and nitrogen fixation in soybean, cowpea, and mungbean. Based on these findings, it can be concluded that cowpea plants treated with the consortium containing DPS-7 and Cc5 showed significantly increased root colonization efficiency, resulting in enhanced growth and yield. Identification of potential actinobacteria using 16S rRNA gene sequencing The treatment exhibiting the highest yield was considered as the most effective consortium and molecular identification of the component isolates (DPS-7 and Cc5) was conducted by 16S rRNA gene sequence analysis. Homology search of nucleotide sequences showed maximum homology of DPS-7 with Streptomyces fumigatiscleroticus and Cc5 with Streptomyces sp. strain PAS3. Conclusion This study highlights the potential of actinobacterial consortia as effective biofertilizers for promoting cowpea growth. The isolation, screening, and evaluation of actinobacterial isolates demonstrated significant plant growth-promoting activities, including solubilization of minerals, nitrogen fixation, production of phytohormones and siderophores. Among the evaluated consortia, the T2 consortium, composed of Streptomyces fumigatiscleroticus and Streptomyces sp. strain PAS3, showed the most promising results in enhancing cowpea growth and yield. These findings suggest that actinobacterial consortia can serve as eco-friendly alternatives to chemical fertilizers, contributing to sustainable agricultural practices. However, conducting field trials is essential to formulate effective biofertilizers and plant growth-promoting strategies for use in commercial crop production systems. Abbreviations PGP – Plant growth promoting IAA – Indole-3-acetic acid HCN – Hydrogen cyanide CRD – Completely randomized design Declarations Ethics approval Not applicable Conflict of Interest The authors have no conflicts of interest Consent to participate The authors consent is obtained Consent for publication The manuscript is being submitted with the consent of all the authors Funding This research was carried out as part of a student project, with no funding provided Acknowledgements This work was conducted as a part of post graduate research work supported by Kerala Agricultural University Authors contributions Niveditha N. L : Conducted the research, preparation of manuscript Dr. D. Girija : Research supervisor, guided research, thesis and assisted in writing manuscript Dr. K. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5368610","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":377662218,"identity":"8f10d67d-cc13-41a1-94c6-cc397e8a3a12","order_by":0,"name":"Niveditha Nelamangala Lalithesh","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7ElEQVRIiWNgGAWjYDACZiDmMWBIALIaGD4AOWzsxGkxAGphbGCcAdLCTIxNPAwQLcw8MEPwAXN2HsMHbwr+5PHPbmx7bPNrmzwfMwPjh485uLVYNvMYG84xMCiWuHOw3Ti377ZhGzMDs+TMbbi1GBxmS5MG+iWx4UZim3Ruz21GoBY2Zl78WtJ/g7TMB2mx7LltT4QW5mPMIC0bQFoYftxOJEbLYck5BsaJG4FaJHsbbie3MTM24/fL+YONH978kUucdyP5mMSPP7dt57c3H/zwEY8WVMDYBiYbiFUPAn9IUTwKRsEoGAUjBQAAeF1PfxIMwVYAAAAASUVORK5CYII=","orcid":"https://orcid.org/0009-0001-1968-5594","institution":"KAU: Kerala Agricultural University","correspondingAuthor":true,"prefix":"","firstName":"Niveditha","middleName":"Nelamangala","lastName":"Lalithesh","suffix":""},{"id":377662219,"identity":"737f27d9-d6ff-4982-9f4f-b63a81ab531e","order_by":1,"name":"Girija Devaki","email":"","orcid":"","institution":"Kerala Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Girija","middleName":"","lastName":"Devaki","suffix":""},{"id":377662220,"identity":"51246278-bd12-446d-aab3-cda51f879c1e","order_by":2,"name":"Kulkarni Surendra Gopal","email":"","orcid":"","institution":"Kerala Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Kulkarni","middleName":"Surendra","lastName":"Gopal","suffix":""},{"id":377662221,"identity":"166922a2-4198-4a4c-82c3-c410bb261e68","order_by":3,"name":"Reshmy Vijayaraghavan","email":"","orcid":"","institution":"Kerala Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Reshmy","middleName":"","lastName":"Vijayaraghavan","suffix":""},{"id":377662222,"identity":"ba43883d-d9f4-4f16-816d-9a68307451b9","order_by":4,"name":"Bobby Unnikrishnan","email":"","orcid":"","institution":"Kerala Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Bobby","middleName":"","lastName":"Unnikrishnan","suffix":""}],"badges":[],"createdAt":"2024-10-31 18:00:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5368610/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5368610/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":70464811,"identity":"65033259-e225-4235-be14-998a6155a4da","added_by":"auto","created_at":"2024-12-03 12:22:50","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":40387,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eNumber of morphotypes obtained from various samples\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5368610/v1/b394f2b15a8fbdc370ee9809.png"},{"id":70465818,"identity":"57ae9037-64e1-4fab-8c92-a604b1742e8c","added_by":"auto","created_at":"2024-12-03 12:31:06","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":273188,"visible":true,"origin":"","legend":"\u003cp\u003eColony morphology of isolates. (a) DPS-7, (b) Cc4 (c) Cc6\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5368610/v1/65511e14a7dfdb0c2fc1c956.png"},{"id":70464814,"identity":"57956c58-174c-4b08-b0c5-a49cbbf84f88","added_by":"auto","created_at":"2024-12-03 12:22:50","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":298960,"visible":true,"origin":"","legend":"\u003cp\u003eDiffusible pigment production by actinobacterial isolates. (a) Cc1 and (b) Cc6\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5368610/v1/f886c8a8b176e14d0c6c2c3b.png"},{"id":70465817,"identity":"5d27e502-681f-419c-ac90-24c9d5b3682c","added_by":"auto","created_at":"2024-12-03 12:31:06","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":166599,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of actnobacterial consortia on biometric parameters (A-J) in cowpea. Values were expressed as mean ± standard error. Different letters indicate significant differences at \u003cem\u003eP\u003c/em\u003e ≤ 0.05 and treatments with same letters are not significantly different. A: plant height; B: number of leaves per plant; C: number of branches per plant: D: number of effective nodules per plant: E: fresh weight of shoot; fresh weight of root; G: dry weight of shoot; H: dry weight of root: I: days to flowering; J: root volume.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eT1: \u003c/strong\u003eConsortium 1 (DPS-7 + Cc-5); \u003cstrong\u003eT2\u003c/strong\u003e: Consortium 2 (WA-27 + Cc-2); \u003cstrong\u003eT3\u003c/strong\u003e: Consortium 3 (Cc-5 + Cc-6); \u003cstrong\u003eT4\u003c/strong\u003e: Consortium 4 (WA-26 + DPS-5); \u003cstrong\u003eT5\u003c/strong\u003e: Consortium 5 (Cc-4 + DPS-7); \u003cstrong\u003eT6\u003c/strong\u003e: PGPR Mix 1 of KAU; \u003cstrong\u003eT7\u003c/strong\u003e: Control (uninoculated)\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5368610/v1/dcf62fc5cfef3c5d87a305d5.png"},{"id":70464815,"identity":"70d33e55-4469-4c4b-b200-e005a8850f53","added_by":"auto","created_at":"2024-12-03 12:22:50","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":81954,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of actnobacterial consortia on yield parameters (a-e) in cowpea. Values were expressed as mean ± standard error. Different letters indicate significant differences at \u003cem\u003eP\u003c/em\u003e ≤ 0.05 and treatments with same letters are not significantly different. (a) number of pods per plant, (b) number of seeds per pod, (c) test weight of seeds, (d) fresh weight of pods and (e) dry weight of pods.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eT1: \u003c/strong\u003eConsortium 1 (DPS-7 + Cc-5); \u003cstrong\u003eT2\u003c/strong\u003e: Consortium 2 (WA-27 + Cc-2); \u003cstrong\u003eT3\u003c/strong\u003e: Consortium 3 (Cc-5 + Cc-6); \u003cstrong\u003eT4\u003c/strong\u003e: Consortium 4 (WA-26 + DPS-5); \u003cstrong\u003eT5\u003c/strong\u003e: Consortium 5 (Cc-4 + DPS-7); \u003cstrong\u003eT6\u003c/strong\u003e: PGPR Mix 1 of KAU; \u003cstrong\u003eT7\u003c/strong\u003e: Control (uninoculated)\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5368610/v1/d17098a751eddbd72e094407.png"},{"id":81400390,"identity":"f97ca85a-ce43-4ba7-953b-b75fb2509cda","added_by":"auto","created_at":"2025-04-25 16:26:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2770663,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5368610/v1/e93f1300-8037-477f-9083-5bd5fe8c425e.pdf"},{"id":70464812,"identity":"6d0957a5-130c-47da-822d-da04e9c37865","added_by":"auto","created_at":"2024-12-03 12:22:50","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":14611,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarytable1.docx","url":"https://assets-eu.researchsquare.com/files/rs-5368610/v1/524d4712ec605391716e79bb.docx"}],"financialInterests":"","formattedTitle":"Exploring the Potential of Actinobacteria as Plant Growth Promoters in Cowpea","fulltext":[{"header":"Introduction","content":"\u003cp\u003eCowpea (\u003cem\u003eVigna ungiculata\u003c/em\u003e L.) known as the black-eyed pea or southern pea is a member of \u003cem\u003eLeguminosae\u003c/em\u003e family is an annual grain legume native from Africa, cultivated as main crop and also as an intercrop in India. It is a protein-rich crop that complements staple cereal for human and fodder for livestock and also provides soil improvement benefits through nitrogen fixation. Despite being an important pulse crop, its productivity has been quite low due to various biotic and abiotic constraints. This global crop encounters a number of operational constraints, including pests and diseases that limit its production and yield potentials from seedling to harvest (Asiwe 2006). To address these challenges, sustainable and eco-friendly approaches are being explored. One promising strategy involves harnessing the plant growth-promoting (PGP) potential of actinobacteria.\u003c/p\u003e \u003cp\u003eThe indiscriminate use of chemical inputs has been linked to detrimental consequences for human and environmental health (Glick, 2012). The introduction of chemical inputs can have lasting impacts on plant evolution by altering the symbiotic relationships between plants and their microbiota, potentially influencing the co-evolution of the holobiont (Rosenberg \u003cem\u003eet al\u003c/em\u003e. 2009) and compromising plant resilience. Therefore, there is an indispensable need for sustainable alternatives, particularly through the application of beneficial microorganisms. Many plant growth-promoting bacteria are readily available in the market, but actinobacteria have limited commercial application. The role of actinobacteria in crop improvement assures a promising future in the field of plant growth promotion and disease management in various crops. The application of actinobacteria in agriculture has increased, due to their ability to promote plant growth and interact beneficially with plant rhizospheres (Yadav \u003cem\u003eet al\u003c/em\u003e. 2018).\u003c/p\u003e \u003cp\u003eActinobacteria are a group of Gram-positive bacteria, terrestrial or aquatic, having high guanine and cytosine content in their DNA. Most of the actinobacteria are saprophytes, ubiquitous and are one of the most diverse groups of bacteria in nature. Their nature varies from anaerobic unicellular organisms to aerobic, filamentous and spore forming lineages (Lewin \u003cem\u003eet al\u003c/em\u003e. 2016). The morphology of actinobacteria varies from unicellular forms to complex filamentous forms, resembling fungi. Some actinobacteria produce spores by asexual reproduction. Hence many scientists hypothesize that they represent a transitional state between bacteria and fungi. Actinobacteria are among the plant growth promoting rhizobacteria (PGPR) equipped with multifunctional PGP traits and many properties beneficial to plant growth (El-Tarabily and Alkhajeh, 2019). These beneficial bacteria can stimulate plant growth under abiotic and biotic stress conditions \u003cem\u003evia\u003c/em\u003e mechanisms such as the production of phytohormones, siderophores, ACC (1-aminocyclopropane-1-carboxylate) deaminase, exopolysaccharides, organic acids, nitrogen fixation, phosphate solubilization, various osmolytes, systemic resistance induction, etc (Khoshmanzar \u003cem\u003eet al\u003c/em\u003e. 2020).\u003c/p\u003e \u003cp\u003eActinobacteria have been widely recognized for their plant growth-promoting (PGP) potential in crops such as tomato, wheat, rice, bean, chickpea, and pea. Passari \u003cem\u003eet al\u003c/em\u003e. (2015) highlighted the potential of \u003cem\u003eStreptomyces\u003c/em\u003e sp. (BPSAC34) as plant growth-promoting agent. Greenhouse experiments demonstrated the efficacy of these strains in stimulating growth and development of chilli (\u003cem\u003eCapsicum annuum\u003c/em\u003e L.), with notable improvements in key growth parameters. Hu \u003cem\u003eet al\u003c/em\u003e. (2020) demonstrated the efficacy of \u003cem\u003eStreptomyces\u003c/em\u003e sp. TOR3209 in promoting tomato growth and yield. Similarly, Vo \u003cem\u003eet al\u003c/em\u003e. (2021) reported that four actinobacterial strains (\u003cem\u003eMicrobispora\u003c/em\u003e sp. CP56, \u003cem\u003eActinomadura\u003c/em\u003e sp. CP84B, and \u003cem\u003eStreptomyces\u003c/em\u003e spp. CP200B and CP21A) significantly improved chickpea growth and nodulation. Researchers at International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) have isolated and characterized PGP actinobacteria from herbal vermicomposts, demonstrating their \u003cem\u003ein vitro\u003c/em\u003e PGP properties (Srinivas \u003cem\u003eet al\u003c/em\u003e. 2021). Further investigations under controlled greenhouse and field conditions validated their effectiveness in enhancing growth and productivity in rice, sorghum, chickpea, and pigeon pea. Our study focused on isolation, screening, and characterization of actinobacteria from soil and compost samples to elucidate their potential as plant growth promoters in cowpea.\u003c/p\u003e"},{"header":"Material and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eIsolation of actinobacteria from soil and compost samples\u003c/h2\u003e \u003cp\u003eSamples were collected from seven different sources including cowpea rhizosphere soil (CR) from Thrissur district, ginger rhizosphere soils (S) from Wayanad district, mangrove forest soil (MS) from Kadappuram (Chettuva) of Thrissur district, uncultivated soil (US) from Kerala Agricultural University (KAU) campus, Vellanikkara, Thrissur, compost (C), coir pith compost (Cc) and vermicompost (VC) from Thrissur district. Actinobacteria were isolated and enumerated from various samples using serial dilution and plating method (Johnson and Curl, 1972) on starch casein agar (HiMedia Laboratories, Mumbai, India). The Petri plates were incubated at 28\u0026thinsp;\u0026plusmn;\u0026thinsp;2 \u003csup\u003eo\u003c/sup\u003eC for a period of five to 12 days. Pure cultures of a total of 50 morphotypes were maintained, including isolates from the repository at the Department of Agricultural Microbiology, KAU, Vellanikkara for further studies.\u003c/p\u003e \u003cp\u003e \u003cb\u003eIn vitro\u003c/b\u003e \u003cb\u003escreening of actinobacteria for plant growth promoting (PGP) activities\u003c/b\u003e\u003c/p\u003e \u003cp\u003eAll the 50 actinobacterial isolates were subjected to primary and secondary screening for various direct plant growth promoting activities including production of indole-3-acetic acid (IAA), nitrogen fixation, solubilisation of phosphate, potassium and zinc, and also indirect PGP activities such as production of hydrogen cyanide (HCN), ammonia and siderophores under \u003cem\u003ein vitro\u003c/em\u003e conditions. Primary (qualitative) screening identified actinobacterial isolates with desired activities, whereas secondary (quantitative) screening measured the extent of these activities by measuring the concentration of the mineral solubilized and IAA produced.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePrimary and secondary screening of actinobacterial isolates for direct PGP activities\u003c/h3\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eIAA production\u003c/h2\u003e \u003cp\u003eActinobacterial isolates were screened for the production of IAA (Ahmad \u003cem\u003eet al\u003c/em\u003e. 2008). The pink colour development in Luria-Bertani (LB) broth indicated positive reaction for IAA production and it was measured for optical density (OD) at 530 nm using a spectrophotometer. The OD values were plotted on a standard graph to obtain the quantity of IAA produced by the isolates and expressed as mg ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of broth.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eNitrogen fixation\u003c/h3\u003e\n\u003cp\u003eFifty actinobacterial isolates were streaked onto N-free Jensen's agar medium, and the plates were incubated at 28\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C for six days. Isolates that exhibited growth on the nitrogen-free medium were classified as nitrogen fixers. Their ability to grow was observed and rated as follows: excellent (++++), good (+++), moderate (++), poor (+), and no growth (-). Further, Nitrogen fixation by the selected isolates was quantified by micro-Kjeldahl method (Jackson, 1973 and Bremner, 1960).\u003c/p\u003e\n\u003ch3\u003ePhosphate solubilization\u003c/h3\u003e\n\u003cp\u003eAll the fifty actinobacterial isolates were screened for phosphate solubilization on Pikovskaya\u0026rsquo;s agar (Nguyen \u003cem\u003eet al\u003c/em\u003e. 1992). Isolates exhibiting potential phosphate solubilization ability in preliminary screening were further assessed for quantitative phosphate solubilization using the phospho-molybdic blue colorimetric method (Olsen \u003cem\u003eet al\u003c/em\u003e. 1962).\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003ePotassium solubilisation\u003c/h2\u003e \u003cp\u003eThe fifty isolates obtained were screened for K solubilization on Aleksandrov\u0026rsquo;s agar (Nguyen \u003cem\u003eet al\u003c/em\u003e. 1992). The quantity of potassium by the potential actinobacteria was determined by flame photometry (Sugumaran and Janarthanam, 2007).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eZinc solubilisation\u003c/h3\u003e\n\u003cp\u003eThe fifty isolates were evaluated for their ability to solubilize zinc on Tris minimal salt agar amended with 0.1% of insoluble zinc oxide (Saravanan \u003cem\u003eet al\u003c/em\u003e. 2004).\u003c/p\u003e\n\u003ch3\u003eScreening of actinobacterial isolates for indirect PGP activities\u003c/h3\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eHCN production\u003c/h2\u003e \u003cp\u003eHydrogen cyanide production was estimated using Luria-Bertani (LB) agar supplemented with glycine (4.4 g glycine/L) as per the method described by Lorck (1948). Petri plates were sealed with parafilm and incubated for 7 to 12 days at 28\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003csup\u003eo\u003c/sup\u003eC. After incubation, development of reddish-brown color on the filter paper indicated positive for HCN production.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eSiderophore production\u003c/h2\u003e \u003cp\u003eAll actinobacterial isolates were assessed for siderophore production on Chrome Azurol Sulfonate (CAS) agar medium (Schwyn and Neilands, 1987). After seven days of incubation, colonies that produced yellow to orange halos were positive for siderophore production.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eAmmonia production\u003c/h2\u003e \u003cp\u003eFreshly grown actinobacterial isolates were inoculated to a sterilized 4% peptone water and incubated at 28\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003csup\u003eo\u003c/sup\u003eC for three to four days. After incubation, 0.5 ml of Nessler\u0026rsquo;s reagent was added to each tube. The development of orange to the brown colour indicated ammonia production (Cappucino \u003cem\u003eet al\u003c/em\u003e. 1992).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eSelection of potential actinobacteria for further characterization\u003c/h2\u003e \u003cp\u003ePromising isolates for plant growth promotion were selected based on ranking of PGP traits (Backer, 2021). Isolates of actinobacteria were arranged on the basis of their IAA production, in decreasing order. A score of 10 was allotted to each of the PGP traits and sum of the scores were considered for ranking of the isolates. Isolates having highest ranking were selected and were subjected to further characterization.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eCharacterization of the selected potential isolates\u003c/h2\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003eMorphological and cultural characterization\u003c/h2\u003e \u003cp\u003eThe selected actinobacteria were grown on starch casein agar media at 28\u003csup\u003eo\u003c/sup\u003eC for seven days and characterized by observing colony appearance and the types of aerial hyphae. The color of spore masses and the production of pigments were also assessed. Gram staining was performed using the method outlined by Hucker and Conn (1923). Gram reaction and spore chain morphology were observed under the compound microscope of 100x magnification.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eBiochemical characterization\u003c/h2\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003eOxidase test\u003c/h2\u003e \u003cp\u003eThe isolates were smeared on oxidase disc (Hi-media DD018-1VL). Appearance of violet colour within 5\u0026ndash;10 seconds at 25-30\u003csup\u003eo\u003c/sup\u003eC indicated positive reaction. A colour change after 60 seconds or no colour change considered as negative.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eCatalase test\u003c/h2\u003e \u003cp\u003eSmear of the isolates prepared in a clean glass slides and a drop of hydrogen peroxide (3%) was added. Cultures that immediately showed effervescence were treated as positive. (Taylor and Achanzar, 1972).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eUtilization of sugars\u003c/h2\u003e \u003cp\u003eFermentation broth (containing glucose, sucrose and mannitol) was prepared in test tubes. Durham\u0026rsquo;s tubes were placed in an inverted position in the broth. The isolates were inoculated in broth and uninoculated control was also maintained. Three replications were maintained and incubated for 37\u003csup\u003eo\u003c/sup\u003eC for 5 days. A change in colour from red to yellow and appearance of bubbles indicated positive for fermentation tests (Cowan, 1974).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003eMolecular characterization\u003c/h2\u003e \u003cp\u003eThe identification of the best performing consortia in pot culture evaluation was carried out by 16s rRNA gene sequencing. Genomic DNA was isolated using Nucleospin\u0026reg; Tissue Kit (Macherey-Nagel). Evaluation of quality of isolated DNA was carried out by agarose gel electrophoresis (Sambrook \u003cem\u003eet al\u003c/em\u003e. 1989). After the separation of DNA bands using electrophoresis, the gels were visualized in a UV transilluminator and the image was taken under UV light using gel documentation system. The PCR product was then purified and sequenced at Rajiv Gandhi Centre for Biotechnology, Trivandrum using the primer 16S-RS-F and 16S-RS-R. The sequencing reaction of the PCR product was done in a PCR thermal cycler (GeneAmp PCR System 9700, Applied Biosystems) using the BigDye Terminator v3.1 Cycle Sequencing kit (Applied Biosystems, USA). The sequence quality was checked using Sequence Scanner Software v1 (Applied Biosystems). Sequence alignment and required editing of the obtained sequences were carried out using Geneious Pro v5.1 (Drummond \u003cem\u003eet al\u003c/em\u003e. 2010). Sequence analysis and nucleotide homology of each isolates were identified through the BLASTn (basic local alignment search tool) programme of NCBI (National Centre for Biotechnology Information) (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://www.ncbi.nlm.nih.gov\u003c/span\u003e\u003cspan address=\"http://www.ncbi.nlm.nih.gov\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). The accession sharing maximum homology with the query sequence was used to identify the isolates.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eCompatibility of potential actinobacterial isolates with plant growth-promoting (PGP) activities\u003c/h2\u003e \u003cp\u003eThe compatibility of the promising actinobacterial isolates was assessed using the \u003cem\u003ein vitro\u003c/em\u003e cross-streak method. One actinobacterial isolate was streaked as a line on a starch-casein agar plate, while another test isolate was streaked perpendicularly to the first. The plates were incubated at 30\u0026deg;C for three days, and the growth of actinobacteria at the intersection was examined. A merger of the actinobacterial growth at this junction indicated compatibility, whereas inhibition zone indicated non-compatibility among the isolates (Al-Hussini \u003cem\u003eet al\u003c/em\u003e. 2019).\u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003ePreparation of talc based actinobacterial consortia\u003c/h2\u003e \u003cp\u003eMost efficient and promising isolates were selected for the preparation of talc based consortia. Talc was sterilized at 121\u0026deg;C and 15 psi for two hours, then mixed with compatible two or three actinobacterial cultures at a concentration of 10\u003csup\u003e8\u003c/sup\u003e CFU ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in a 1:2.5 ratio.\u003c/p\u003e \u003cp\u003e \u003cb\u003eIn planta\u003c/b\u003e \u003cb\u003eevaluation of actinobacterial consortia for growth promotion in cowpea\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe five actinobacterial consortia were assessed under sterile conditions for their efficacy in growth promotion of cowpea. The experiment was carried out from June to August 2024, using completely randomized design (CRD), The experiment consisted of seven treatments with three replicates, and each replicate had three pots. The first five treatments comprised the selected consortia, whereas the sixth and seventh treatments included PGPR Mix 1 from KAU and an uninoculated control, respectively. Sterile potting mixture was used for the experiment. Seeds of Bhagyalakshmy variety were treated with the KAU culture of \u003cem\u003eRhizobium\u003c/em\u003e sp. (strain Rh4), with three to four seeds sown in each pot. The soil was inoculated with the talc based actinobacterial consortia twice, initially one week after sowing and again one month after the first application. The population of actinobacteria in the potting mixture was evaluated at 30, 60 and 90 days after sowing (DAS). Observations on biometric parameters such as plant height, number of leaves, number of branches, days to flowering, number of effective nodules per plant were recorded at monthly intervals for three months after sowing. Fresh and dry weight of shoots, root parameters like fresh and dry weight of roots and root volume were recorded at 90 DAS. Yield parameters such as number of pods per plant, number of seeds per pod, test weight, fresh and dry weight of pods were observed after 90 DAS. Initial and final nutrient (N, P and K in kg ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) profile of the potting mixture and nutrient status of plants after the experiment were recorded.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eAnalysis of variance (ANOVA) suitable to CRD was performed on the collected data using GRAPES version 1.0.0 (Gopinath \u003cem\u003eet al\u003c/em\u003e. 2021) statistical software.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cp\u003e\u003cstrong\u003eIsolation of actinobacteria\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eModern agriculture needs sustainable practices to increase crop yields, boost production, and enhance soil fertility (Yasari \u003cem\u003eet al\u003c/em\u003e. 2009). Actinobacteria can function as bio-inoculants and biopesticides, serving as an eco-friendly alternative to chemical fertilizers, by aiding crops in tolerating stress factors such as temperature, pH, salinity, and drought. (Cheng \u003cem\u003eet al\u003c/em\u003e. 2018). These findings encouraged us to take up the present study which focuses on isolation, screening, and characterization of actinobacteria from rhizosphere soil, uncultivated soil, mangrove forest soil and compost samples to assess their potential as promoters of plant growth in cowpea. Among the various soil and compost samples analysed,\u0026nbsp;cowpea rhizosphere soil (CR) recorded significantly superior actinobacterial population on starch casein agar, with a population of 42.9 x 10\u003csup\u003e6\u0026nbsp;\u003c/sup\u003ecfu g\u003csup\u003e-1\u003c/sup\u003e. Coirpith compost (Cc) recorded the population of 19.0 x 10\u003csup\u003e6\u003c/sup\u003e cfu g\u003csup\u003e-1\u003c/sup\u003e. The lowest population was recorded in mangrove forest soil (MS) and ginger rhizosphere soil (S) with a population of 1.1x10\u003csup\u003e6\u0026nbsp;\u003c/sup\u003ecfu g\u003csup\u003e-1\u003c/sup\u003e and 1.2x10\u003csup\u003e6\u0026nbsp;\u003c/sup\u003ecfu g\u003csup\u003e-1\u003c/sup\u003e. In contrast, coir pith compost and ginger rhizosphere soil reported a significantly higher number of morphotypes (7), while mangrove forest soil recorded lowest number of morphotypes (1).\u003c/p\u003e\n\u003cp\u003eNumerous studies support the findings of this research. Khamna \u003cem\u003eet al\u003c/em\u003e. (2010) isolated 270 \u003cem\u003eStreptomyces\u003c/em\u003e spp. from the rhizosphere soils of 14 Thai medicinal plants. Gopalakrishnan \u003cem\u003eet al\u003c/em\u003e. (2012) reported that actinobacterial isolates obtained from herbal vermicompost can be employed for the biological control of \u003cem\u003eFusarium\u003c/em\u003e wilt of chickpea. Sreevidya \u003cem\u003eet al\u003c/em\u003e. (2016) isolated and characterized actinobacteria with plant growth-promotion, from the rhizosphere of chickpea. Actinobacteria are susceptible to low pH (ideal pH range: 6.5-8.0) and acidity, as well as wet conditions. These are mesophilic organisms that thrive at 25-30˚C, whereas some species that are frequently found in compost and manures are thermophilic and grow at 55-65˚C (e.g. \u003cem\u003eThermoactinomycetes\u003c/em\u003e, \u003cem\u003eStreptomyces\u003c/em\u003e) (Bhatti \u003cem\u003eet al\u003c/em\u003e.\u003cem\u003e\u0026nbsp;\u003c/em\u003e2017). Meanwhile, Wolińska \u003cem\u003eet al\u003c/em\u003e. (2019) reported that greater abundance of actinobacteria was observed in non-cultivated soils relative to the cultivated soils. \u0026nbsp; Moreover, it was indicated that the actinobacterial diversity depended on both the soil genesis and the land use; however, this effect directly depended on the particular family and genera. Redox potential (Eh) and total carbon (TC) both seemed to significantly impact the diversity of actinobacteria. Nalini \u003cem\u003eet al\u003c/em\u003e. (2020) reported that among the 40 actinobacterial isolates isolated from the different rhizosphere soil samples of legume crop, cowpea was rich in the actinobacteria population and starch casein agar proved to be the best medium for their enumeration. Law \u003cem\u003eet al\u003c/em\u003e. (2023) reported a novel strain, \u003cem\u003eStreptomyces\u003c/em\u003e \u003cem\u003egriseiviridis\u003c/em\u003e MUM 136J\u003csup\u003eT\u003c/sup\u003e from a mangrove forest soil in Malaysia. Recently, Uesugi \u003cem\u003eet al\u003c/em\u003e. (2024) isolated and characterized actinobacteria from industrial composting soil of oil palm (\u003cem\u003eElaeis guineensis\u003c/em\u003e) in the municipality of Igarap\u0026eacute;-A\u0026ccedil;u, Par\u0026aacute;.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;In vitro\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;screening of actinobacterial isolates for plant growth promoting (PGP) traits\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eActinobacteria are known for synthesizing large amounts of phytohormones that enhance plant growth. Additionally, they play a crucial role in mobilizing nutrients like phosphate, zinc, and potassium in soils deficient in these micronutrients, thus significantly contributing to plant growth promotion (Mitra \u003cem\u003eet al\u003c/em\u003e. 2022). As PGPR, actinobacteria utilize both direct and indirect mechanisms to enhance plant growth. Therefore, they can be regarded as plant biofertilizers (Franco-Correa and Chavarro-Anzola, 2016). \u003cem\u003eIn vitro\u003c/em\u003e primary and secondary screening for direct PGP activities revealed that among 50 isolates, only nine produced IAA with amount ranging between 11.3 and 90.9 mg ml\u003csup\u003e-1\u003c/sup\u003e. The isolate ACT-3 (90.9\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003emg ml\u003csup\u003e-1)\u003c/sup\u003e was found to be significantly superior to all other isolates. There are many reports which demonstrated the ability of actinobacteria to produce IAA and thus promote plant growth (Solans \u003cem\u003eet al\u003c/em\u003e. 2011; Dochhil \u003cem\u003eet al\u003c/em\u003e. 2013). Suksaaid \u003cem\u003eet al\u003c/em\u003e. (2017) reported that 51% of the mangrove actinobacterial isolates produced IAA in the range of 0.2 mg ml\u003csup\u003e-1\u003c/sup\u003e to 165.7 mg ml\u003csup\u003e-1\u003c/sup\u003e. Fourty eight isolates were predicted to fix atmospheric nitrogen where 15 isolates were strong nitrogen fixers. Four isolates \u003cem\u003eviz.\u0026nbsp;\u003c/em\u003eDPS-7, MS-3(1)\u003cem\u003e,\u003c/em\u003e Cc-4 and CR-3 recorded significantly superior nitrogen fixation (Table 1).\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eThere are numerous evidences of actinobacteria involved in nitrogen fixation. The genus \u003cem\u003eFrankia\u003c/em\u003e are widespread endophytic actinobacteria symbiotically associated with plant roots and fix atmospheric nitrogen for host plants (Benson and Silvester, 1993). In agriculture, biological phosphate solubilization serves as an important alternative to the use of natural phosphates, enhancing nutrient uptake efficiency. In this study, fifteen isolates exhibited phosphate solubilization, while potassium solubilization was observed in two isolates (US3 and VC5). These results are supported by many studies, Anwar \u003cem\u003eet al\u003c/em\u003e. (2016), screened actinobacterial isolates for their phosphate solubilizing abilities and revealed that \u003cem\u003eStreptomyces\u003c/em\u003e sp. WA-1 produced the highest soluble phosphate concentration (72.1 mg/100 ml), followed by \u003cem\u003eS. djakartensis\u003c/em\u003e TB-4 (70.3 mg/100 ml). Etesami \u003cem\u003eet al\u003c/em\u003e. (2017) reported that only 5% of potassium solubilizing bacteria available are actinobacteria. Archana (2007) isolated 30 potassium-solubilizing bacterial strains from soils in the Belgaum and Dharwad districts of Karnataka, using mica as an insoluble potassium source and potassium solubilization by the actinobacterial isolates varied from 2.4 to 44.4 \u0026mu;g ml⁻\u0026sup1;. In our study, none of the isolates showed the ability for zinc solubilisation on Tris minimal salt agar medium supplemented with 0.1% insoluble zinc oxide under \u003cem\u003ein vitro\u0026nbsp;\u003c/em\u003econditions. However, Patel and Thakker (2020) found that \u003cem\u003eStreptomyces nanhaiensis\u003c/em\u003e strain YM4 was capable of solubilizing zinc, with a concentration of 41.16 ppm.\u003c/p\u003e\n\u003cp\u003eMicroorganisms promote plant growth indirectly by producing compounds, such as siderophores, ammonia, HCN, and hydrolytic enzymes, which inhibit plant pathogens and reduce disease (Hayat \u003cem\u003eet al\u003c/em\u003e. 2010). In our study, development of an orange to brown colour in 12 actinobacterial isolates (CS-4, CS-1, CS-6, WA-7, C2, S4-5, VC-5, DPS-5, CR-3, VC-4, CT-3, and DPS-6) following the addition of Nessler\u0026apos;s reagent indicated the production of ammonia. Kaur \u003cem\u003eet al\u003c/em\u003e. (2013) made similar observations, by detecting ammonia production in 12 out of 62 actinobacterial isolates. The production of siderophores by various soil actinobacteria retains iron in the soil environment and makes it available to the plants (Nimaichand \u003cem\u003eet al\u003c/em\u003e. 2016). In addition, 9 isolates (US-3, US-4, C1, S2(2), WA-26, WA-22, CS-6(2), S4-2 and VC-5) produced siderophores but none of the isolates produced HCN. Sreevidya \u003cem\u003eet al\u003c/em\u003e. (2016) isolated 89 actinobacteria and found that four \u003cem\u003eStreptomyces\u003c/em\u003e strains produced significant quantities of siderophores, which improved plant growth and yield in field trials. Hydrogen cyanide has also been reported to play an important role in mineral mobilization and phosphate release, indirectly enhancing nutrient availability for both actinobacteria and their host plants (Rijavec and Lapanje, 2016)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1\u0026nbsp;\u003c/strong\u003eRanking of actinobacterial isolates based on IAA production, N fixation and solubilisation of phosphate and potassium\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"602\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eIsolates\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eIAA production\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(\u0026micro;g ml\u003csup\u003e-1\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAmount of nitrogen fixed\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(mg of N g\u003csup\u003e-1\u003c/sup\u003e of C utilised)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eQuantity of P solubilized\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(\u0026micro;g ml\u003csup\u003e-1\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eQuantity of K solubilized\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(\u0026micro;g ml\u003csup\u003e-1\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTotal score\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eRanking\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eAct-3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e90.90\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e909.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e16\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eCc5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e53.83\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e91.87\u003csup\u003ef\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e1457.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eUS3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e28.08\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e93.09\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e3.86\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e1250.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eVC5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e25.50\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e3.53\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e290.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eCR5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e17.66\u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e176.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e19\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eC1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e16.68\u003csup\u003ef\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e166.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eVC4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e15.63\u003csup\u003eg\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e156.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e21\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eWA-25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e14.47\u003csup\u003eh\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e144.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eEK9K1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e11.30\u003csup\u003ei\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e94.25\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e1055.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e5\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eCs-1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e92.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e921.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e12\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eCc1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e95.10\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n 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96px;\"\u003e\n \u003cp\u003e91.16\u003csup\u003ei\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e911.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e15\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eWA-30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e91.41\u003csup\u003eh\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n 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style=\"width: 78px;\"\u003e\n \u003cp\u003eDPS-7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e15.42\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e91.88\u003csup\u003ef\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e934.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e11\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eWA-27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n 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style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e958.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e8\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eCc6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e12.84\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e93.88\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e1067.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n 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style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e12.84\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e91.64\u003csup\u003eg\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e1044.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e6\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eMS-3(1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e15.39\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e153.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e22\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eS3-2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e5.13\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e51.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e27\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eCR3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e15.36\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e153.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e23\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eWA-22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e5.14\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e51.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e26\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eS3-1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e2.57\u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e25.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eS4-2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e5.13\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e51.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e28\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eS1-3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e10.24\u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e102.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 78px;\"\u003e\n \u003cp\u003eCc3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 90px;\"\u003e\n \u003cp\u003e5.13\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 96px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e51.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e29\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e*\u003cem\u003eTreatments with same letters are not significantly different\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSelection of efficient PGP actinobacteria for further characterization and \u003cem\u003ein planta\u0026nbsp;\u003c/em\u003eevaluation\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe isolates with first 15 ranks (US3, Cc4, Cc6, EK9K1, DPS-5, WA-26, Cc2, Cc1, WA-27, DPS-7, CS-1, Cc5, WA-30, CS-10, and ACT-3) were selected as the most efficient ones after ranking the isolates and were used for further characterization of actinobacteria followed by \u003cem\u003ein planta\u0026nbsp;\u003c/em\u003eevaluation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCharacterization of actinobacterial isolates\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eActinobacterial isolates were characterized morphologically using Gram staining, which confirmed that they were Gram-positive and exhibited a filamentous structure. Cultural and morphological characteristics of actinobacteria are given in Table 2 and Fig. 2. Li \u003cem\u003eet al\u003c/em\u003e. (2016) reported that actinobacteria produce two type of pigments water-soluble or diffusible pigment and fat-soluble or non-diffusible pigment. In our study, diffusible pigment production was observed in Cc1 and Cc6 (Fig. 3) and non-diffusible pigments were not reported. However, Thampi and Bhai (2017) stated that colony morphology is influenced by the type of media used, and therefore, cannot be considered a fundamental criterion for identifying microbes. Biochemical characterization of the isolates are presented in Table 3. In a similar study, Vyawahare \u003cem\u003eet al\u003c/em\u003e. (2013) found that nine \u003cem\u003eStreptomyces\u003c/em\u003e strains tested positive for both catalase and oxidase activity.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2\u0026nbsp;\u003c/strong\u003eMorphological and cultural characterization of isolates\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"530\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eIsolates\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eColony\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003ecolour\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eElevation\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eForm\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMargin\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGram\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003estaining\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePigment\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eproduced\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eCc1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eLight brown\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eRaised\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eCircular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eEntire\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eYellow\u003c/p\u003e\n \u003cp\u003e(diffusible)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eCc2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eGrey\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eFlat\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eCircular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eFiliform\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eCc4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eCreamish\u003c/p\u003e\n \u003cp\u003ewhite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eRaised\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eCircular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eEntire\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eCc5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eGrey\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eUmbonate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eCircular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eEntire\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eCc6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eOff white\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eUmbonate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eCircular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eEntire\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eLight yellow\u003c/p\u003e\n \u003cp\u003e(diffusible)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eUS3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eCreamish\u003c/p\u003e\n \u003cp\u003ewhite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eUmbonate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eCircular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eCurled\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eWA-26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eWhite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eUmbonate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eIrregular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eCurled\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eDPS-7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eGrey\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eRaised\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eIrregular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eCrateriform\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eCS-1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eCreamish\u003c/p\u003e\n \u003cp\u003ewhite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eUmbonate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eCircular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eFiliform\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eEK9K1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eWhitish ash\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eConvex\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eCircular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eFiliform\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eCS-10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eGrey\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eRaised\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eCircular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eEntire\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eWA-30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eOff white\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eSlightly raised\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eCircular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eEntire\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eDPS-5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eWhite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eUmbonate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eConcentric\u003c/p\u003e\n \u003cp\u003ering\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eEntire\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eWA-27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eGrey\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eUmbonate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eCircular\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eFiliform\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eAct-3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eBlackish\u0026nbsp;\u003c/p\u003e\n \u003cp\u003ebrown\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003eCircular\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003eConvex\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 70px;\"\u003e\n \u003cp\u003eCurled\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 62px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 88px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3\u0026nbsp;\u003c/strong\u003eCharacterization of isolates based on biochemical tests\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"529\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eIsolates\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 95px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCatalase\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 85px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eOxidase\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 265px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eUtilization of sugars\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eGlucose\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSucrose\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMannitol\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eCc2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eCc4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eCc5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eCc6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eDPS-5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eDPS-7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eWA-26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eWA-27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eEK9K1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eCS-1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eCS-10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eWA-30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eWA-9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eCc1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eUS3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e+\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003eACT-3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 85px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eCompatibility of potential actinobacteria with PGP activities\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo develop the consortia formulation of PGP actinobacteria, compatibility among 15 selected isolates was tested by using cross streak method. All possible combinations of nine promising isolates were tested and the results revealed that among 15 isolates, only eight were showing compatibility. From this, five best combination of two isolates (Cc-5 and Cc-6; DPS-7 and Cc-5; DPS-7 and Cc-4; DPS-5 + WA-26; WA-27 and Cc-2) were selected for the preparation of talc-based consortia for further \u003cem\u003ein planta\u003c/em\u003e evaluation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eIn planta\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;evaluation of selected actinobacterial consortia for growth promotion in cowpea\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA pot culture experiment was conducted to evaluate the effect of five actinobacterial consortia in enchancing cowpea growth and yield. The abundance of actinobacterial population in the rhizosphere of cowpea at different intervals is given in the figure1. The population of actinobacteria ranged from 1.1 x10\u003csup\u003e6\u003c/sup\u003e cfu g\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003eto 6.0 x10\u003csup\u003e6\u003c/sup\u003e cfu g\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003eand T\u003csub\u003e2\u003c/sub\u003e and T\u003csub\u003e5\u003c/sub\u003e were statistically significant at all the intervals. No actinobacteria could be detected in the treatments T\u003csub\u003e6\u003c/sub\u003e (PGPR Mix 1 of KAU)\u003csub\u003e\u0026nbsp;\u003c/sub\u003eand T\u003csub\u003e7\u0026nbsp;\u003c/sub\u003e(uninoculated control) at 30, 60 and 90 DAS.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4\u003c/strong\u003e Population of actinobacteria in the rhizosphere of cowpea at various intervals (x10\u003csup\u003e6\u003c/sup\u003e cfu g\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"559\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 171px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTreatments\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e30 DAS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e60 DAS\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e90 DAS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 171px;\"\u003e\n \u003cp\u003eT\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e5.7\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.755\u003csup\u003ea\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e4.4\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.650\u003csup\u003eb\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e4.1\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.6127\u003csup\u003ea\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 171px;\"\u003e\n \u003cp\u003eT\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e6.0\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.781\u003csup\u003ea\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e5.6\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.748\u003csup\u003ea\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e4.2\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.630\u003csup\u003ea\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 171px;\"\u003e\n \u003cp\u003eT\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e4.3\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.633\u003csup\u003eb\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e3.7\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.568\u003csup\u003ec\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e3.1\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.501\u003csup\u003eb\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 171px;\"\u003e\n \u003cp\u003eT\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e3.6\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.562\u003csup\u003eb\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e3.4\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.534\u003csup\u003ec\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e2.1\u003csup\u003ebc\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.439\u003csup\u003ebc\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 171px;\"\u003e\n \u003cp\u003eT\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cdiv align=\"center\"\u003e5.7\u003csup\u003ea\u003c/sup\u003e \u003cbr\u003e(0.757\u003csup\u003ea\u003c/sup\u003e)\u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e5.2\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.722\u003csup\u003ec\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e2.5\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e(0.397\u003csup\u003ec\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 171px;\"\u003e\n \u003cp\u003eT\u003csub\u003e6\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e0\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e0\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 171px;\"\u003e\n \u003cp\u003eT\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e0\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e0\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 171px;\"\u003e\n \u003cp\u003eLSD (0.05)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e1.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e0.735\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 132px;\"\u003e\n \u003cp\u003e0.426\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eLog transformed values are given in parentheses. Means followed by common letter(s) do not significantly differ.\u003c/p\u003e\n\u003cp\u003eActinobacterial inoculation significantly improved all the growth and yield parameters compared to the control treatment (\u003cem\u003eP\u003c/em\u003e \u0026le; 0.05). At 90 DAS, significantly higher plant height was observed in T\u003csub\u003e1\u003c/sub\u003e, T\u003csub\u003e2\u003c/sub\u003e, T\u003csub\u003e3\u003c/sub\u003e, and T\u003csub\u003e4\u003c/sub\u003e. Number of leaves per plant was significantly higher in T\u003csub\u003e1\u003c/sub\u003e, T\u003csub\u003e2\u003c/sub\u003e, and T\u003csub\u003e3\u003c/sub\u003e, while T\u003csub\u003e2\u003c/sub\u003e had the most branches. T\u003csub\u003e2\u003c/sub\u003e and T\u003csub\u003e3\u003c/sub\u003e recorded significantly higher fresh shoot weight. T\u003csub\u003e1\u003c/sub\u003e, T\u003csub\u003e2\u003c/sub\u003e, T\u003csub\u003e3\u003c/sub\u003e, and T\u003csub\u003e4\u003c/sub\u003e recorded higher fresh root weight, whileT\u003csub\u003e2\u003c/sub\u003e and T\u003csub\u003e3\u003c/sub\u003e recorded significantly higher dry root weight. Significantly higher root volume was observed in T\u003csub\u003e1\u003c/sub\u003e, T\u003csub\u003e2\u003c/sub\u003e, and T\u003csub\u003e6\u003c/sub\u003e. Time taken for\u0026nbsp;flowering varied significantly among treatments. Earliest flowering (43.7 days) was noticed in T\u003csub\u003e1\u003c/sub\u003e,\u0026nbsp;whereas it was longest in T\u003csub\u003e3\u003c/sub\u003e (46.5 days). At 60 DAS, T\u003csub\u003e1\u003c/sub\u003e recorded maximum number of nodules (37.9), followed by T\u003csub\u003e2\u0026nbsp;\u003c/sub\u003e(31.7) and T\u003csub\u003e3\u0026nbsp;\u003c/sub\u003e(28.2) (Fig. 4). Meanwhile,\u0026nbsp;yield parameters such as number of pods (23.8), number of seeds per pod (12.1), test weight (22.8 g), fresh and dry weight of pods (120.2 g and 15.6 g) were also superior in T\u003csub\u003e2\u003c/sub\u003e, indicating their potential benefits for plant growth and yield (Fig. 5). Nutrient analysis of the plant samples also revealed that T2 recorded the\u0026nbsp;highest N, P and K content of 55.43, 124.8 and 74.4 Kg ha-\u003csup\u003e1\u003c/sup\u003e respectively (Table 4). Post-experimental soil analysis revealed a significant increase in available phosphorus content in the potting mixture.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 5\u0026nbsp;\u003c/strong\u003eEffect of actinobacterial isolates on final nutrient status of plants under pot culture\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"529\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 245px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTreatments\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNitrogen\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e(kg ha\u003csup\u003e-1\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePhosphorus\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(kg ha\u003csup\u003e-1\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePotassium\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e(kg ha\u003csup\u003e-1\u003c/sup\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 245px;\"\u003e\n \u003cp\u003eT\u003csub\u003e1\u003c/sub\u003e: Consortium 1 (DPS-7 + Cc-5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e41.65\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e98.88\u003csup\u003ebcd\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e59.87\u003csup\u003ebc\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 245px;\"\u003e\n \u003cp\u003eT2:\u0026nbsp;Consortium 2 (WA-27 + Cc-2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e55.43\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e124.84\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e74.44\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 245px;\"\u003e\n \u003cp\u003eT\u003csub\u003e3\u003c/sub\u003e: Consortium 3 (Cc-5 + Cc-6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e49.74\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e109.39\u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e63.09\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 245px;\"\u003e\n \u003cp\u003eT\u003csub\u003e4\u003c/sub\u003e: Consortium 4 (WA-26 + DPS-5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e45.78\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e83.30\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e54.68\u003csup\u003ebc\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 245px;\"\u003e\n \u003cp\u003eT\u003csub\u003e5\u003c/sub\u003e: Consortium 5 (Cc-4 + DPS-7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e45.71\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e91.40\u003csup\u003ead\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e60.59\u003csup\u003ebc\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 245px;\"\u003e\n \u003cp\u003eT\u003csub\u003e6\u003c/sub\u003e: PGPR Mix 1 of KAU\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e46.04\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e104.23\u003csup\u003ebc\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e51.08\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 245px;\"\u003e\n \u003cp\u003eT7: \u0026nbsp;Control (uninoculated)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e43.23\u003csup\u003ecd\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 95px;\"\u003e\n \u003cp\u003e91.82\u003csup\u003ecd\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e52.78\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThis finding supports the results of several earlier studies. A study employing the \u0026quot;ragdoll\u0026quot; method investigated the impact of four \u003cem\u003eStreptomyces\u003c/em\u003e spp. on chickpea seedling growth, revealed VAI-7 as the most effective strain in enhancing shoot and root lengths. Under field conditions, the \u003cem\u003eStreptomyces\u003c/em\u003e spp. increased nodule number over un-inoculated control demonstrating a direct proof for enhancing nitrogen fixation. The \u003cem\u003eStreptomyces\u003c/em\u003e strains used in the study exhibited increase in agronomic properties such as the shoot weight, leaf weight, leaf area, plant height, grain yield and stover yield over the un-inoculated control (Sreevidya \u003cem\u003eet al\u003c/em\u003e. 2016). Previously it was reported that the culture filtrates of \u003cem\u003eStreptomyces\u003c/em\u003e \u003cem\u003eolivaceoviridis\u003c/em\u003e containing IAA stimulated growth and yield of wheat plants (Aldesuquy \u003cem\u003eet al\u003c/em\u003e. 1998) and \u003cem\u003eStreptomyces\u003c/em\u003e spp. from a tomato rhizosphere had the ability to produce IAA and improve tomato growth by increasing root dry weight (El-Tarabily, 2008). Htwe \u003cem\u003eet al\u003c/em\u003e. (2019) observed that inoculation with \u003cem\u003eStreptomyces griseoflavus\u003c/em\u003e enhanced agronomic traits, nodulation, and nitrogen fixation in soybean, cowpea, and mungbean. Based on these findings, it can be concluded that cowpea plants treated with the consortium containing DPS-7 and Cc5 showed significantly increased root colonization efficiency, resulting in enhanced growth and yield. \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIdentification of potential actinobacteria using 16S rRNA gene sequencing\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe treatment exhibiting the highest yield was considered as the most effective consortium and molecular identification of the component isolates (DPS-7 and Cc5) was conducted by 16S rRNA gene sequence analysis. Homology search of nucleotide sequences showed maximum homology of DPS-7 with \u003cem\u003eStreptomyces\u003c/em\u003e \u003cem\u003efumigatiscleroticus\u003c/em\u003e and Cc5 with \u003cem\u003eStreptomyces\u003c/em\u003e sp. strain PAS3.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study highlights the potential of actinobacterial consortia as effective biofertilizers for promoting cowpea growth. The isolation, screening, and evaluation of actinobacterial isolates demonstrated significant plant growth-promoting activities, including solubilization of minerals, nitrogen fixation, production of phytohormones and siderophores. Among the evaluated consortia, the T2 consortium, composed of \u003cem\u003eStreptomyces fumigatiscleroticus\u003c/em\u003e and \u003cem\u003eStreptomyces\u003c/em\u003e sp. strain PAS3, showed the most promising results in enhancing cowpea growth and yield. These findings suggest that actinobacterial consortia can serve as eco-friendly alternatives to chemical fertilizers, contributing to sustainable agricultural practices. However, conducting field trials is essential to formulate effective biofertilizers and plant growth-promoting strategies for use in commercial crop production systems.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003ePGP \u0026ndash; Plant growth promoting\u003c/p\u003e\n\u003cp\u003eIAA \u0026ndash; Indole-3-acetic acid\u003c/p\u003e\n\u003cp\u003eHCN \u0026ndash; Hydrogen cyanide\u003c/p\u003e\n\u003cp\u003eCRD \u0026ndash; Completely randomized design\u0026nbsp;\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no conflicts of interest\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors consent is obtained\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe manuscript is being submitted with the consent of all the authors\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was carried out as part of a student project, with no funding provided\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was conducted as a part of post graduate research work supported by Kerala Agricultural University\u003c/p\u003e\n\u003cp\u003eAuthors contributions\u003c/p\u003e\n\u003cp\u003eNiveditha N. L : Conducted the research, preparation of manuscript\u003c/p\u003e\n\u003cp\u003eDr. D. Girija : Research supervisor, guided research, thesis and assisted in writing manuscript\u003c/p\u003e\n\u003cp\u003eDr. K. Surendra Gopal : Research committee member, provided guidance in research and manuscript preparation\u003c/p\u003e\n\u003cp\u003eDr. Boby Unnikrishnan : Research committee member, provided guidance in research and manuscript\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDr. Reshmy Vijayaraghavan : Research committee member, provided guidance in conducting research\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAhmad F, Ahmad AI, Khan MS (2008) Screening of free-living rhizospheric bacteria for their multiple plant growth promoting activities. Microb. 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Sci. 5(5): 786-793.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"plant growth promotion, actinobacteria, cowpea, consortia, compost.","lastPublishedDoi":"10.21203/rs.3.rs-5368610/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5368610/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe study includes isolation, characterization and evaluation of actinobacteria for plant growth promotion in cowpea. Actinobacteria were isolated from four soil and three compost samples on starch casein agar and total 50 morphotypes were maintained including 21 isolates from the Department of Agricultural Microbiology repository. All 50 isolates were subjected to screening for direct plant growth promoting (PGP) activities including nitrogen fixation, phosphate, potassium and zinc solubilization and production of indole-3-acetic acid. Indirect PGP activities including production of hydrogen cyanide, ammonia and siderophores were also tested under \u003cem\u003ein vitro\u003c/em\u003e conditions. Compatibility among isolates was tested \u003cem\u003evia\u003c/em\u003e cross-streak method and five actinobacterial consortia were developed for further \u003cem\u003ein planta\u003c/em\u003e studies. A total of 29 actinobacterial isolates were obtained from rhizosphere soil and compost samples, with cowpea rhizosphere soil exhibiting the highest population density. Based on \u003cem\u003ein vitro\u003c/em\u003e screening and PGP ranking of all the 50 isolates, 15 isolates with PGP ability were selected for further cultural, biochemical and morphological characterization. The evaluation of five compatible consortia led to significant improvement in growth and yield parameters of cowpea compared to treatment of PGPR Mix 1 and control (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026le;\u0026thinsp;0.05). T\u003csub\u003e2\u003c/sub\u003e consortium (\u003cem\u003eStreptomyces fumigatiscleroticus\u003c/em\u003e and \u003cem\u003eStreptomyces\u003c/em\u003e sp. strain PAS3) recorded significantly higher number of pods (23.8), number of seeds per pod (12.1), test weight (22.8 g), fresh (120.2 g) and dry weight (15.6 g) of pods, indicating their potential benefits for plant growth and yield. This research suggested actinobacterial consortia as viable biofertilizers, enhancing cowpea growth and contributing to environmentally sustainable agriculture.\u003c/p\u003e","manuscriptTitle":"Exploring the Potential of Actinobacteria as Plant Growth Promoters in Cowpea","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-03 12:22:45","doi":"10.21203/rs.3.rs-5368610/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"62f3a97e-9c2d-46de-a69f-0fa4a1b8e700","owner":[],"postedDate":"December 3rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-04-25T16:18:32+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-03 12:22:45","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5368610","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5368610","identity":"rs-5368610","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}