Effect of the plant growth-promoting bacteria strain Bacillus mojavensis I4 on potato growth, physiology, tuber yield and quality under salt stress conditions

Effect of the plant growth-promoting bacteria strain Bacillus mojavensis I4 on potato growth, physiology, tuber yield and quality under salt stress conditions | 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 Effect of the plant growth-promoting bacteria strain Bacillus mojavensis I4 on potato growth, physiology, tuber yield and quality under salt stress conditions Jaweher Sdiri Ghidawi, Imen Ghazala, Anissa Haddar, Oumaima Bouazizi, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3883973/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 25 Nov, 2024 Read the published version in Potato Research → Version 1 posted 4 You are reading this latest preprint version Abstract Salinity is one of the major threats to potato. As the first vegetable crop, improving its production under salinity stress is with great interest. In a previous work, Bacillus mojavensis I4 (BmI4) plant growth-promoting (PGP) bacterial strain was isolated from the soil. Since BmI4 showed a growth capacity under salt conditions (10% NaCl) we decided here to evaluate its PGP capacity on potato plants (Spunta and Claustar varieties) grown in the greenhouse in the presence of 100 mM NaCl. Stem elongation and diameter, leaf number, area and organ fresh weights were monitored during 40 days of culture as well as tuber yield, caliber and composition. Our results showed that the inoculation of plantlet roots with BmI4 enhanced plant growth under salinity, particularly for Spunta variety. These beneficial effects were associated with an increase of auxin levels in plants from both varieties. The assessment of H 2 O 2 and malondialdehyde contents revealed that BmI4 inoculation led to reduced oxidation in plants submitted to salinity, via the increase of superoxide dismutase, catalase and peroxidase activities. Moreover, the BmI4 treatment enhanced proline accumulation especially in leaves of Spunta variety. BmI4 inoculated plants from Spunta variety exhibited an early induction of tuberization associated with an increase of tuber yield and caliber under both culture conditions. These findings suggest that inoculation of potato with BmI4 can be promising strategy to improve plant culture in saline areas. Moreover, inoculation improved tuber composition. Potato Salinity Plant growth-promoting bacteria Auxin stimulation Plant production Tuber quality Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Global crop yield decreases by seventy percent due to environmental stresses (Neshat et al. 2022 ), among which salinity is frequent and considered the most devastating for the plants (Kesawat et al. 2023 ). Aproximately 7% of land area and 33% of irrigated lands worldwide are affected by salinity (Chele et al. 2021 ). High soluble salt contents can alter soil fertility by causing retardation of plant growth and development (Abbas et al. 2019 ; Numan et al. 2019). Salt affects plants by interfering with many physiological and metabolic functions such as nitrogen fixation, ionic and water homeostasis, lipid metabolism, photosynthesis and protein synthesis (Li and Jian 2017; Hmaied et al. 2019). The accumulation of salt in the roots zone causes osmotic stress and disrupts cell ion homeostasis by inducing both the inhibition of essential elements uptake such as K + , Ca 2+ and NO 3 − and the accumulation of toxic elements such as Na + and Cl − (Paranychianakis and Chartzoulakis 2005 ). Sodium is the most soluble and widespread element in salty soils. Its high accumulation in plants limits water conductance disturbs intracellular potassium influx and nutrient balance (Kumar et al. 2020 ). The overproduction of reactive oxygen species (ROS) is the most frequent consequence of salt stress (Kesawatt et al. 2023). ROS (e.g. hydroxyl radical (HO • ), superoxide radical (O 2 • − ), single oxygen (O 2 1 ) and hydrogene peroxide (H 2 O 2 )) are highly reactive and at high amounts, noxious, leading to destrutive processes in cells (Kesawatt et al. 2023) restricting cell division and elongation (Egamberdieva et al. 2017 ). Among vegetables, potato ( Solanum tuberosum L.) is the largest crop growing in 79% countries (FAO 2015 ) ranked third after wheat and rice (FAO 2019 ). However, this crop faces important challenges with salinity (Handayani et al. 2019 ), which affects negatively vegetative growth of plants leading to instability of tuberization and yielding through the inhibition of the formation and the swelling of tubers (Dahal et al. 2019 ). To ensure sustainable production under salt stress conditions, inoculation of plants with plant growth–promoting bacteria (PGPB) has attracted attention as an alternative strategy, that is reliable method, ecologically mild and environnmenntally safe (Ali et al. 2022 ). The inoculation with beneficial microorganisms may provide naturally drived solution to salinity and climate change by modulating crop development and preserving multiple associated ecosystems services (Liu et al. 2023 ). The use of beneficial microbes such as PGPB in agriculture production systems started a long time ago and there is increasing evidence that it can enhance plant tolerance to adverse environmental stresses (Batool et al. 2020 ). Some PGPB that cope with salinity (halotolerant strains), can be involved efficiently in physiological and biochemical pathways of plant response to salt stress (Abbas et al. 2019 ). PGPB can potentially alleviate environmental stress effects such as salinity at several stages of plant growth through a variety of mechanisms. These bacteria are known to produce the indole-3-acetic acid (IAA) auxin phytohormone. They provide minerals such as nitrogen, phosphate and potassium, siderophore production (Mishra et al. 2021 ; Nashat et al. 2022 ; Cappellari et al. 2023 ). They can produce expolysaccharides (EPS) and volatile organic compounds (VOC) that play important role in plant protection. In this context, this study aims to investigate the effect of Bacillus mojavensis I4 (BmI4; Ghazala et al. 2016 ) PGPB on potato plant growth, tuber yield and quality under greenhouse culture conditions in the absence or presence of salt stress (100 mM NaCl). Morphological, physiological and biochemical parameters were monitored on Spunta (Sp) and Claustar (Cl) varieties. Plant growth and physiological parameters were measured during 40 days of culture. Moreover, we focused on the effect of PGPB on tuberization timing, tuber yield and quality under salt stress conditions. The antioxidant enzyme activities were followed since they are involved in control of ROS accumulation under stressful conditions. Superoxide dismutase (SOD), catalase (CAT) and peroxidase (GPX) are the main enzymes that play a major role in the self defense in plants (Mishra et al. 2023 ). SOD is the main antioxidant as it activates the first line of defense against ROS-induced damage by converting superoxide into hydrogen peroxide, followed by CAT and GPX degrading H 2 O 2 (Del Rio et al. 2018). The PGPB provide plants tolerance to stress by enhancing the activity of the antioxidant enzymes and other non-enzymatic antioxidants (Gururani et al. 2013 ; Chatterjee et al. 2017 ). Material and methods Plant material The study was carried out on two potato varieties Spunta (Sp), the most cultivated in Tunisia (80%; Azouz 1996) and also one of the most widely grown potatoes in the world (elornplants.com), and Claustar (Cl) variety. These plants were multiplied in vitro on MS medium (Murashige and Skoog 1962 ) added with Morel vitamins (Morel and Wetmore 1951 ) at a temperature varying from 22°C to 24°C and a photoperiod of 12h/days under a light intensity of 62 µE/m 2 s. Bacterial inoculum Plantlet roots were inoculated with Bacillus mojavensis I4 (BmI4) strain isolated from the soil of Sfax city in Tunisia and identified in the laboratory (accession number KF012872; Ghazala et al. 2016 ). This isolate was selected on the basis of its capacity to promote the growth of wheat plants by allowing the production of siderophores and IAA, as well as the fixation of nitrogen and the solubilization of phosphate. In addition, this strain tolerates a temperature of 55°C, 50 mg/l Cd and 10% NaCl (Ghazala et al. 2023 ), making it an excellent candidate for mitigating the effect of saline stress on plants. The BmI4 strain was cultivated on LB broth medium at 37°C and maintained at 4°C before use. Plant inoculation, cultivation and application of salt stress Plantlets of the two potato varieties, approximately three weeks-old and sufficiently rooted in MS medium, were inoculated by soaking their roots for 20 min in the BmI4 strain suspension (10 6 cfu/ml) previously prepared in PBS buffer (137 mM NaCl, 2.7 mM KCl, 8 mM Na 2 HPO 4 , and 2 mM KH 2 PO 4 ) for 20 min. Control plantlets which had the same age and length were treated with PBS buffer. These inoculated and non-inoculated plantlets (control) were transferred in plastic pots (12 cm in diameter) containing an autoclaved mixture of 50% sand and 50% peat (Potgrond H: Klasmann Deilmann, Geeste, Germany), and watered with tap water at a rate of 50 ml/pot twice a week. After 15 days of greenhouse acclimatization, the inoculated and non-inoculated plant groups were each divided into two groups to study the response to salt stress. Thus, the plants of each potato variety were arranged in 4 batches which underwent different treatments: Non-inoculated plants not subjected to salinity (control: C - ) Inoculated plants not subjected to salinity (C + ) Non-inoculated plants subjected to salinity (SS - ) Inoculated plants subjected to salinity (SS + ) To apply salt stress in batches (2) and (4), the plants were irrigated with 50 ml salt solution (100 mM NaCl) twice a week the 15 days of the acclimatization until the cycle end. Whereas plants of batches (1) and (3) were kept watered with tap water. Plant culture was conducted between March 11and May 25 (2023), in a greenhouse in the presence of sunlight. Plant growth parameters Plant growth was evaluated for 40 days from the beginning of the treatment by measuring stem length and diameter, leaf number and area on seven plants previously selected from each batch. The tuber yield (g/plant) was also determined on these plants at the end of the cycle (60 days). At 10, 25 and 40 days of treatment, seven plants were used to measure each of leaf, stem and root fresh weights, physiological parameters and tuber weight. Determination of chlorophyll contents Total chlorophyll was extracted from fresh leaves (0.01g) ground in acetone (Arnon. 1949). After centrifugation at 12000 rpm for 15 min, the supernatant containing the pigments was collected and the absorbance of the samples was determined at 645 nm and 663 nm. The content of chlorophylls a (Chl a), b (Chl b) and total chlorophyll (Chl t) were determined according to the following formulas: Chl a (µg/g FW) = [12.7* A663 − 2.69 *A645]*V/FW Chl b (µg/g FW) = [22.9* A645 − 4.68 *A663]*V/FW Chl t (µg∕g FW) = Chl a + Chl b with FW: fresh weight of leaves; V: volume of sample Detrermination of malondialdehyde (MDA) content Lipid peroxidation was determined as thiobarbituric acid (TBA) reactive metabolites mainly MDA in leaves and roots as described by Hodges et al ( 1999 ). The fresh leaves and roots (0.15 g) were homogenized in 1.5 ml of trichloroacetic acid (TCA) 0.1%. After centrifugation at 12000 rpm for 30 min at 4°C, the supernatant was mixed with 2 ml of TBA/TCA solution (0.8% TBA and 15% TCA dissolved in 0.25 N HCl). The mixture was heated at 100°C for 15 min and then centrifuged at 12000 rpm for 10 min. The amont of MDA was measured spectrophotometrically at 532 and 600 nm, calculated using a standard curve and expressed as nmol/g FW. Determination of H 2 O 2 levels The H 2 O 2 content in leaves and roots was determined according to Lereto and Velikova (2001) method. The fresh leaves and roots (0.1 g) were ground in the presence of 2 ml TCA 0.1%. The extracts were centrifuged at 12000 rpm for 15 min. An aliquot of 0.5 ml of the supernatant was supplemented with 0.5 ml of potassium phosphate buffer (10 mM K 2 HPO 4 , 10 mM KH 2 PO 4 , pH 7) and 1 ml of KI (1 M). The absorbance was measured at 390 nm and H 2 O 2 content was calculated using a standard curve and expressed as µmol/g FW. Preparation of protein extract The fresh leaves and roots (0.1 g) were ground in a mortar with 1ml Tris HCl buffer (67 mM, pH 8). After centrifugation at 12000 rpm at 4°C 30 min, the supernatant was used to assess SOD, GPX and CAT activities (Kammoun et al. 2017 ). Protein concentration in the extract was determined using the Bradford method (Kruger 1994). Determination of SOD activity The superoxide dismutase (SOD) activity was determined by monitoring the inhibition of the photo-reduction of Nitro Blue Tetrazolium (NBT) (Dhindsa et al. 1981 ). The reaction mix contained 50 mM phosphate buffer (pH 7), 2.64 mM NBT, 0.26 mM riboflavin and Na 2 EDTA-methionine. The photo-reduction of NBT was measured at 560 nm and the SOD activity was expressed as units per milligram of protein. The amount of SOD inhibiting the reaction rate by 50% was defined as one SOD unit. Determination of CAT activity The CAT activity was assayed by following the consumption of H 2 O 2 at 240 nm (Aebi 1984 ). The reaction mix contained 100 µl of protein extract in 1880 µl of 0.1 M phosphate buffer supplemented with 100 µl H 2 O 2 (10 mM) (Jbir-koubaa et al. 2015 ). One unit of catalase activity was defined as the amount that decomposes one µmol of H 2 O 2 . Determination of GPX activity The GPX activity was measured as described by Floh and Gunzler ( 1984 ). Indeed, 200 µl of enzyme extract were mixed with 400 µL of glutathione (GSH) solution 0.1 mM and 200 µl of phosphate buffer (67 mM, pH 7.8). The mixture was incubated at 25°C for 5 min, then 200 µL of H 2 O 2 (1.3 mM) were added and incubation pursued for 10 min. The reaction mixture was then supplemented with 1 ml TCA (1%). After centrifugation at 3000 rpm for 10 min at 4°C, 480 µl of the supernatant was mixed with 2.2 ml of Na 2 HPO 4 (0.32 M) and 320 µl of 5,5’-dithio-bis-(2-nitrobenzoic acid) (DTNB) (10 mM). The oxidized glutathione (GSSG) produced was determined by measuring the absorbance at 412 nm (Kammoun et al. 2017 ). The GPX activity was calculated as follows: µmol reduced GSH disappeared /min/mg of protein = [(OD sample-OD control/OD control)*(0.04*5/X*10)] with X : protein concentration (mg/ml) ; 0.04 : initial quantity of reduced GSH ; 5: to move from activity in 200 mL to activity in 1 ml; 10 : reaction time Determination of auxin concentration The fresh leaves and roots (0.1g) were homogenized in 1 ml of ethanol. After centrifugation at 12000 rpm for 30 min at 4°C, the supernatant was mixed with 2 ml of Salkowki’s reagent. The absorbance was measured at 530 nm. The auxin content was determined using a standard curve of IAA and expressed as µg/g FW (Ghazala et al, 2023 ). Determination of proline content Proline content was measured according to Bates et al. ( 1973 ). The fresh mass (0.1g) from leaves and roots was ground in 4 ml sulfosalicylic acid (3%) and centrifuged at 10000 rpm for 30 min. The supernatant was then mixed with 1 ml glacial acetic acid and 1 ml ninhydric acid. After incubation at 100°C for 1 h, 2 ml of toluene were added. The absorbance of upper phase was measured at 520 nm. The proline amount was calculated from a standard curve and expressed as mmol/g FW. Determination of tuber yield, number, caliber, eyes number and skin color Tubers of Sp plants grown under the different conditions were collected and weighted. The tuber yield (g/plant) was determined during the 40 days of monitoring and at the end of the cycle (60 days). Tuber number and caliber as well as number of eyes were determined on tubers harvested at the final step. The skin color of these tubers was also measured using a Chroma Meter CR-400/410 colorimeter (Konica Minolta). Three orthogonal coordinates define this parameter: the clarity index L* and the chromatic coordinates a* (red) and b* (yellow). They were determined by scanning the potato skin at five locations. Determination of dry matter The percentage of tuber dry matter of tubers was determined after drying for 72 h at 80°C. Dry matter content was determined using the following formulae: DW × 100/FW with FW : fresh weight; DW : dry weight Chemical analysis of tubers Lipid, total nitrogen and ash contents of potato tubers were determined according to the American Association of Cereal Chemists 2000 standard methods 46 − 30, 30 − 10 and 08 − 01 respectively (Ben Jeddou et al. 2014 ). The starch content was determined using the enzymatic colorimetric method described by Khabou et al. ( 1996 ). Reducing sugar content was determined by the acid 3, 5-dinitrosalicylic (DNS) method as described by Miller ( 1959 ). Carotenoids content of tubers To extract lipophilic compounds, 0.3 g of fresh tuber mass were ground in liquid nitrogen and then homogenized for 30 min at 4°C in 1.5 ml of acetone. After centrifugation at 10,000 rpm for 10 min at 4°C, the supernatant was collected, and the pellet was re-extracted with the same solvent. The two supernatants were pooled, and the total carotenoid concentration was determined by measuring the absorbance at 450 nm and expressed as µg/g FW (Chiab et al. 2023 ) Statistical analysis All data were presented as the means ± standard deviation (SD) of three independent biological replicates. The comparison between the different values were statistically effectuated by one-way ANOVA test using IBM SPSS Statistics (version 20). Differences were considered significant at P < 0.05. Results Effect of inoculation on growth and morphology The influence of BmI4 strain inoculation on the growth of Sp and Cl plants under greenhouse culture was evaluated under both saline (100 mM NaCl) and standard (0 mM NaCl) conditions by measuring the number, area and fresh weight (FW) of leaves, the elongation, diameter and FW of stems as well as the FW of roots during 40 days. Salinity affected all growth parameters (SS − ) (Supplementary Fig. 1; Fig. 1 , 2 ). The effect of BmI4 strain seems to be more pronounced on the Sp variety, mitigating the effects of salt stress compared to the Cl variety which exhibited very little differences between inoculated and non-inoculated plants. Indeed, the inoculation with BmI4 enhanced stem growth in Sp variety submitted to salt stress for which FW was similar to that of control plants (non-inoculated and grown under standard conditions, C − ) (Fig. 2 ). In addition, stem diameter of the inoculated Sp plants submitted to salt stress (SS + ) seems to be slightly larger than that of control plants (C − ) (Fig. 1 ). In contrast, the BmI4 inoculation did not lead to any significant change of stem elongation in the presence of salt stress. Although salinity reduced leaf growth, it remained equivalent (FW and area of leaves) or even better (number of leaves) in the inoculated than in the control plants of the Sp variety. In addition, BmI4 boosted roots FW of Sp. These results indicate that roots inoculation with BmI4 strain led to more vigorous plants from Sp variety. For Cl variety, most growth parameters in inoculated plants were close to those of non-inoculated plants in the presence of salt stress, well below those in control. Chlorophyll content Due to its crucial role in photosynthesis, the total chlorophyll content was determined in the leaves of the plants subjected to the different treatments (Fig. 3 ). A significant increase of chlorophyll content was observed in Sp plants inoculated with BmI4 and subjected to salt stress. However, in the Cl variety, no significant differences were noticed in chlorophyll contents under the different conditions after 25 days of treatment. Auxin content To better understand the effect of inoculation by BmI4 on Sp and Cl mitigation of salinity effect, the auxins content was measured in leaves and roots of inoculated and non-inoculated plants subjected or not to salinity. The results (Fig. 4 A) showed that auxins were more accumulated in roots than in leaves. Moreover, the inoculation with BmI4 led to higher auxins accumulation in Sp after 10 days of culture under salt stress conditions. These results might explain the enhanced growth observed in these inoculated plants. Proline content Osmotic adjustment is one of the essential mechanisms for the adaptation of plants to saline stress. It can be ensured by the accumulation of compatible solutes in the cells, such as proline. An important increase of proline contents was noticed in leaves of Spunta after 25 days of stress conditions (Fig. 4 B). This increase was more important in inoculated plants. In contrast, low proline amounts were measured in Cl variety during the 40 days of culture for the different treatments. These data suggest that inoculation of plants with BmI4 helps the Sp plants capacity to alleviate salt stress negative effects through the enhancement of proline synthesis. Effect of inoculation on the oxidative stress parameters Among the response parameters to abiotic stress, we considered the accumulation of ROS. Therefore, the MDA and H 2 O 2 contents were assessed in the roots and leaves of inoculated and non-inoculated plants grown in the presence or absence of salt stress at 10, 25 and 40 days. MDA contents remained at low levels in roots of both Sp and Cl plants for all treatments (Fig. 5 A). Salt stress conditions caused MDA increase in plant leaves, while inoculation with BmI4 led to a decrease of MDA levels. Indeed, inoculated plants of both genotypes submitted to salinity exhibited MDA content closed to that of respective control plants and even below in Sp leaves at 40 days. Similarly, almost no significant H 2 O 2 increase was observed in inoculated plant leaves and roots upon the application of salt stress (Fig. 5 B). However, the H 2 O 2 content reached the highest level in non-inoculated plants, and it increased with duration of stress. Effect of inoculation on the antioxidant enzyme activities In order to better understand the plant response, the antioxidant enzymes SOD, CAT and GPX activities were checked in the roots and leaves of both Sp and Cl plants submitted to the different treatments at 10, 25 and 40 days. SOD activity The inoculation of Sp plants with BmI4 resulted in the increase of SOD activity in leaves at 10 days of salt treatment and later on this activity became comparable to that of plants grown in the different conditions (Fig. 6 A). This result can be related to low MDA accumulation. In addition, the SOD activity was stimulated in inoculated Sp roots under salt stress conditions at 25 days and 40 days, whereas in non-inoculated Sp it remained low and close to control (C − ). The leaves of treated Cl plants did not show any increase of SOD activity compared to the respective control plants. However, an increase in SOD activity was measured in the roots of inoculated Cl plants grown under the standard conditions. The low enzyme induction in the roots of BmI4 treated Cl under stress conditions may be explained by the low MDA levels. GPX and CAT activities The GPX and CAT activities increased in both leaves and roots of inoculated Sp plants submitted to salt stress compared to control plants (Fig. 6 B,C). The GPX activity increased with duration of stress while the highest CAT activity increase was noticed after 10 days of salt stress. The GPX and CAT enhancement in Sp may be associated to the low H 2 O 2 content. However, in non-inoculated Sp leaves and roots, these activities increased after 25 days of salt stress, they decreased at 40 days of stress which may explain the significant accumulation of H 2 O 2 during the treatment. In the Cl leaves, inoculation with BmI4 seems to enhance GPX activity at 40 days (Fig. 6 B), whereas it remained at very low levels in non-inoculated leaves under salt stress conditions. The CAT activity remained low in Cl plants treated with NaCl (Fig. 6 C) in inoculated and non-inoculated plants. This can be related to H 2 O 2 amount measured. Evaluation of tuber yield and quality Tuber yield (g/plant) was determined during the culture period (11 March-25 May 2023) for Sp variety since Cl plants were not able to tuberize at this season (Supplementary Fig. 2). Inoculation of plants with BmI4 strain allowed earlier tuber initiation and better yield (Table 1 A). Indeed, after 25 days of culture, tuber development was initiated, whereas only slight swellings in some stolon tips were found on non-inoculated plants. This earlier induction of tuber formation was associated with higher growth rate and final tuber biomass production (60 days). BmI4 inoculation resulted in a gain of final tuber yield under salt stress conditions. The tuber yield of BmI4 inoculated plants submitted to salinity was close to the control (C − ) at the end of culture period (60 days). Similarly the number of tuber per plant of inoculated plants was higher than that of non-inoculated ones either in the presence (3.083 ± 0.135 in inoculated plants vs 1.75 ± 0.048 in non-inoculated plants) or in the absence (3.833 ± 0.021 vs 2.167 ± 0.895) of salt stress. Moreover, the higher caliber of tubers were obtained in inoculated plants and higher number of eyes than non-inoculated plants in both culture conditions (Table 1 B). All these data confirm that BmI4 inoculation enhanced capacity of multiplication in Sp. With regards to tuber skin color (Table 1 B), it seems that salt stress conditions resulted in a decrease of the clarity (L*) and a reduction of yellow color (b*) while the red color (a*) increased. In contrast, the inoculation with BmI4 modulated the clarity by recovery of b* value and increase of a* under salt stress conditions. Effect of inoculation on tuber composition The tuber composition i.e. dry matter, ashes, starch, reducing sugars, lipid, protein, nitrogen and carotenoid contents was analyzed in relation to the different plant treatments. We noticed that inoculation with BmI4 led to an increase of dry matter, starch, ash, protein and carotenoid contents of tubers (Table 2 ). However, salinity affected negatively dry matter, starch and ash contents. The starch and ash content in tubers from inoculated plants submitted to salinity reached levels well above control. Lipid content remained low in all potatoes but total proteins and nitrogen increased significantly with inoculation under salt stress conditions compared to control (C − ). The lowest level of reducing sugars was recorded in tubers obtained from inoculated plants grown in the presence of salt. Tuber carotenoids increased in the different treatments compared to control, the highest percentage was recorded in tubers obtained from inoculated plants subjected to salinity. Table 1 : A . Tuber kinetic production (g/plant) of Spunta plants inoculated (+) or not (-) with Bacillus mojavensis I4 and subjected (SS) or not (C) to salt stress B . Mean number of eyes, caliber and skin color of Spunta tubers of harvested at the end of culture (60d) from plants inoculated (+) or not (-) with Bacillus mojavensis I4 and subjected (SS) or not (C) to salt stress Values are represented by means ± SD. Different letters (a, b, c and d) indicate significant difference between the different treatments (at P < 0.05 , ANOVA test) A 10d 25d 40d 60d C - 0 0 C 0.888 c ± 0.065 1.917 b ± 0.086 SS - 0 0 C 0.502 d ± 0.036 0.527 d ± 0.032 C + 0 0.735 a ± 0.037 3.377 a ± 0.296 4.975 a ± 0.267 SS + 0 0.347 b ± 0.012 1.767 b ± 0.007 1.799 c ± 0.069 B C - SS - C + SS + Mean number of eyes 6 b ± 0.63 3,20 d ± 0.4 8.20 a ± 0.74 4.80 c ± 0.740 Caliber(%) <1.5 cm 17.63 c ± 0.005 75.13 a ± 0.100 0 d 54,04 b ± 0.010 [1.5-3cm] 82.35 b ± 0.010 25.1 d ± 0.010 100 a 45,92 c ± 0.025 Skin color L* 72.51 b ± 0.01 44.95 d ± 0.050 77.34 a ± 0.010 62.5 c ± 0.005 a* 3.77 c ± 0.005 6.32 b ± 0.005 2.98 d ± 0.005 7.12 a ± 0.015 b* 36.34 c ± 0.040 24.26 d ± 0.040 37.47 a ± 0.010 36.53 b ± 0.038 Table 2 : Chemical composition of tubers of final yield (60 days) obtained from Spunta plants inoculated (+) or not (-) with Bacillus mojavensis I4 and subjected (SS) or not (C) to sat stress Values are represented by means ± SD. Different letters (a, b, c and d) indicate significant difference between the different treatments (at P < 0.05 , ANOVA test) C − SS − C + SS + Dry matter (%) 22.05 b ± 0.040 12.59 d ± 0.005 24.66 a ± 0.065 19.15 c ± 0.035 Ashes (%) 1.43 c ± 0.002 0.74 d ± 0.007 1.7 a ± 0.050 1.6 b ± 0.003 Starch (%) 14.62 c ± 0.200 11.42 d ± 0.18 20.02 a ± 0.84 17.02 b ± 0.016 Reducing sugars (%) 0.36 a ± 0.007 0.30 c ± 0.06 0.35 b ± 0.008 0.25 d ± 0.040 Lipids (%) 0.440 c ± 0.005 0.94 a ± 0.03 0.29 d ± 0.004 0.56 b ± 0.010 Total proteins (%) 5.9 c ± 0.050 5.53 d ± 0.08 7.49 b ± 0.01 8.21 a ± 0.080 Total nitrogen (%) 0.94 c ± 0.008 0.88 d ± 0.013 1.19 b ± 0.002 1.313 a ± 0.013 Carotenoids (µg/g FW) 2.56 c ± 0.150 3.2 b ± 0.030 3.25 b ± 0.010 4.35 a ± 0.080 Discussion The increase of food demand with the rise of global population needs the development of sustainable agriculture to improve yields and quality of crops especially under salt stress conditions. Indeed, salt stress is one of the rapidly growing environmental stress over the world (Abbas et al. 2019 ). The use of PGPB in agricultural practices is a viable solution to garantee food demand (Mehmood et al. 2021 ). In the present study, we focused on the effect of the PGPB strain BmI4 inoculation on Sp and Cl potatoes grown under salt stress (100 mM) in the greenhouse. Growth monitoring was carried out by following different traits including stem elongation and diameter, leaf number and area and organ fresh weight. The overall morphologly proved that inoculation with BmI4 strain stimulated growth allowing alleviation of salt stress devastating effect, especially in Sp variety. While salt stress did not lead to any significant decrease of chlorophyll pigments especially in Sp leaves, the inoculation with the BmI4 strain improved significantly total chlorophyll content in Sp plants under saline conditions, might helpful in explaining their better growth. This result further confirm that beneficial bacteria treatment can have positive effect on photosynthetic activity and chlorophyll content (Efthimiadou et al. 2020 ). Similarly, Ghazala et al. ( 2023 ) showed that the chlorophyll increased in salt acclimated wheat treated by BmI4 that suggests photosynthesis enhancement. We also noticed a stability in chlorophyll content with duration of stress (40 days) suggesting that BmI4 inoculation improved plant adaptation to salt stress. Similarly sweet peppers treated with Bacillus thuringiensis MH161336 indicated positive correlation between chlorophyll content and inoculum size (AlKahtani et al. 2020 ). Since, salinity affects tuber formation and bulking due to high salt accumulation in tuber cells, resulting in altered osmotic potential and nutrient uptake capacity (Dahal et al. 2019 ) we evaluated the tuber production capacity of plants under the different culture conditions. Our results showed that BmI4 inoculation allowed higher tuber yield (60 days) in terms of tuber weight and number under control and salinity conditions. Moreover, the higher eyes number on these potatoes may reflect their higher potential for further multiplication. Our results are in agreement with other studies demonstrating the efficiency of Bacillus sp. strains to stimilate the salt stress adaptation in different plant species (Peng et al. 2021 ; Lee et al. 2021 ; Patani et al. 2023 ; Ghazala et al. 2023 ; Öztürk and Dursun 2023 ). Likewise, Gururani et al. ( 2013 ) repported that the use of Bacillus sp. allowed enhancement of potato plant growth. Nookaraju et al. ( 2011 ) reported the positive influence of these strains on in vitro tuberization. Tahir et al. ( 2019 ) revealed that the use of consortium of Bacillus strains increased biomass of potato plant by almost 76% and tuber weight by 84% in saline conditions. In our case, tuber yield per plant (g/plant) increased by 241.3% and tuber weight by 93.6% with the BmI4 inoculation of plants under salinity conditions. The BmI4 inoculation of Sp plants seems to increase precocity of tuberization at 25 days whereas no tubers were found in non-inoculated plants. The observed increase of leaf growth and development in inoculated plants may be correlated with the earliness time of tuber initiation (Odgerel K and Bánfalvi Z 2021 ). Early tuberization was also reported in potato plants inoculated by PGPB by Oswald et al (2011). These authors attributed the increased tuber yields in PGPB treated plants to early tuber induction, leaf area development and increase of photosynthetic rates. Under salinity conditions, the auxin production of BmI4 inoculated plants increased in comparison to the non-inoculated ones. Since BmI4 strain is able to produce IAA (Ghazala et al. 2023 ), it could be the one source of this increasing auxin content which can be related to the better growth and yield. Tahir et al ( 2019 ) showed an increase of indole-compounds in root exsudates of potato plants inoculated with PGPR Bacillus strains as compared to the other treatment under normal and salt affected soil conditions. In addition, these authors demonstrated a correlation between auxins and tuber production. Kolachevskaya et al. ( 2019 ) reported that endogenous auxin confirmed their role in tuber enlargement induction and growth. These processes were tightly linked with a sharp rise of the auxin level in the subapical zone of stolons that were generating tubers. At 25 days, the increase of auxin in inoculated Sp plants was associated with improvement of plant growth and tuber production. However, no tuber formation was observed in non-inoculated plants. In Cl variety, the increase of auxin content in inoculated plants under salinity was correlated with a slight improvement of plant growth. Plant tissue injury generates excess of MDA that can lead to damaging several macromolecules (Juan et al. 2021 ). H 2 O 2 and MDA contents were monitored in the Sp and Cl plants submitted to the different treatments. Results indicate that H 2 O 2 and MDA contents were lower in inoculated plants of both genotypes compared to non-inoculated ones in the presence of salinity. This indicates that BmI4 inoculated plants exhibited better capacity to cope with salinity than control ones. Indeed, in Sp inoculated with BmI4, the SOD, CAT and GPX showed significant increase in comparison to non-inoculated plants explaining the decrease of MDA and H 2 O 2 contents. However, these enzyme activities did not seem to increase with great extent compared to non-inoculated and control plants, thus reflecting the low effect of BmI4 on Cl compared to Sp. These data sugget that to improve production of a potato cultivar it is necessary to select the best host in combination with beneficial bacterial inoculum (Pathak et al. 2019 ). Similarly, Molina-Romero et al. (2020) on maize showed differential responses between varieties, assigned to the bacteria colonization capacity. The BmI4 inoculum size should be optimized on Cl plants. Moreover, for Cl plants, other culture seasons should be considered to obtain tubers. Proline is a biochemical marker of salt stress response in plants (Egamberdieva et al. 2017 ). It is probably one of the most studied amino acids acting against abiotic stress response such as salt by balancing the adverse osmotic potential that prevents water uptake. We noticed a significant increase of proline content in inoculated Sp plant when submitted to 25 days of salt stress. Besides its osmoprotectant role, proline can act as a potent non enzymatic antioxidant (Rejeb et al. 2014 ; Jiménez Arias et al. 2021). The inoculation with BmI4 strain improved Sp tuber nutritional quality in comparison to control, marking great advantageous quotation. Salinity is suggested to decrease tuber dry matter by retardation of carbohydrate translocation from the leaves (Dahal et al. 2019 ). In the fresh market, consumers give great importance to the tuber appearance, whereas the industry processors require traits that confer frying quality such as dry matter, low reducing sugars and absence of physiological disorders. Higher dry matter provides advantages of higher processing yield, less fat absorption, better texture without affecting the taste. On the other hand, low sugar contents prevent the darkening of the processed potato products, which compromises the appearance and flavor of the fried product (Silva et al. 2019 ; Kammoun et al. 2022 ). Tubers obtained in this study from BmI4-treated plants showed the lowest reducing sugars and higher dry matter (19.5%) compared to tubers of non-inoculated plants under salt stress conditions (12.59%). These data suggest that BmI4 inoculation improved tuber quality, which required for processing and culinary use. These tubers from inoculated plants showed the highest carotenoid contents under salt stress conditions, suggesting better antioxidant capacity of these potatoes compared to those of the non-inoculated plants. The increase of total proteins and nitrogen in tubers of plants treated with BmI4 might be related to the bacteria ability of nitrogen fixation (Ghazala et al. 2023 ). Although the above documented evidences indicated that some benefit bacteria strains showed sutable potential to be used for potato growth and yield promotion under salt stress, to the best of our knowledge this is the first report showing this quality improvement. Conclusion This study demonstrated that the BmI4 strain protected potato plants against salt stress. It substantially alleviated salt stress-mediated decrease of the growth and development, more significantly in Sp variety than in Cl. The inoculation resulted in an increase of auxin content and a reduction of oxidative stress (MDA and H 2 O 2 ) in Sp and Cl plants. These factors, together with the enhancement of chlorophyll, proline and antioxidant SOD, CAT, GPX activities, boosted the growth and ultimately resulted in a higher tuber production in Sp variety. Furthermore, the current investigation indicates that BmI4 inoculation promoted tuber quality, thereby adding a new dimension to the benificial effect. Therefore, the application of BmI4 strain may be a promising technique to promote potato crop in saline areas. Declarations Acknowledgement The authors would like to thank the Tunisian Ministry of High Education and Scientific Research for supporting this work. Authors contribution statement JSG effectuated all the expriments with OB. She did the statistical analysis and wrote the first draft of the manuscript. IG and AH identified and characterized the bacterial strain in previous works. They contributed in the preparation of BmI4 inoculum. IG participated in the exprimental step. ONE conceived and designed the research approach and corrected the manuscript. RGB provided suggestions for the experimental design and revised the article prior to submission. All authors have read and approved the final copy of the manuscript. Conflict of interest The authors have no competing interests to declare. Data availability statement The authors confirm that the data supporting the findings of this study are available within the article and supplementary material. References Abbas R, Rasul S, Aslam K, Baber M, Shahid M, Mubeen F, Naqqash T (2019) Halotolerant PGPR: a hope for cultivation of saline soils. 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Ecotox Enviro Saf 178:33–42. https://doi: 10.1016/j.ecoenv.2019.04.027 Supplementary Files SupplementaryFig.1.docx SupplementaryFig.2.docx Cite Share Download PDF Status: Published Journal Publication published 25 Nov, 2024 Read the published version in Potato Research → Version 1 posted Reviewers agreed at journal 08 Jun, 2024 Reviewers invited by journal 24 Jan, 2024 Editor assigned by journal 24 Jan, 2024 First submitted to journal 20 Jan, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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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-3883973","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":269174848,"identity":"c52ee848-e5e5-48cf-93cf-5ca17c7a829b","order_by":0,"name":"Jaweher Sdiri Ghidawi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA90lEQVRIiWNgGAWjYBACxgYGBmYw6zADw4GECiCDmbmBBC0PzoC0MOLXAgIQLQeA+h+2wYzBp7z9jOHjgop79nzHeR8eSJxXG83fDtTyo2Ibbof15BgbzzhTnDjzMLvBgcRtx3NnHGZsYOw5cxuPX3K3SfO2JSQYHGZjAGo5ltsA1MLM2IZHS//b7b95/yXYQ7TMOZY7n6CWGbnbmHkbEhg3gLU01ORuIKzl/WdpnmMJQL8AtSQcO5C7EajlID6/GPanJX7mqUmw5zt/jPnjj5q63HnnDx988KMCj5YGVP5hMHkAp3ogkEfj1+FTPApGwSgYBSMUAAAkfmHwplokowAAAABJRU5ErkJggg==","orcid":"","institution":"National Engineering School of Sfax: Ecole Nationale d'Ingenieurs de Sfax","correspondingAuthor":true,"prefix":"","firstName":"Jaweher","middleName":"Sdiri","lastName":"Ghidawi","suffix":""},{"id":269174849,"identity":"1fac3b33-eb61-4221-8369-b33d293aaa3d","order_by":1,"name":"Imen Ghazala","email":"","orcid":"","institution":"National Engineering School of Sfax: Ecole Nationale d'Ingenieurs de Sfax","correspondingAuthor":false,"prefix":"","firstName":"Imen","middleName":"","lastName":"Ghazala","suffix":""},{"id":269174850,"identity":"b9948c5b-ea94-4b5e-a8c7-659df8999fe8","order_by":2,"name":"Anissa Haddar","email":"","orcid":"","institution":"University of Sfax Higher Institute of Biotechnology of Sfax: Universite de Sfax Institut Superieur de Biotechnologie de Sfax","correspondingAuthor":false,"prefix":"","firstName":"Anissa","middleName":"","lastName":"Haddar","suffix":""},{"id":269174851,"identity":"8a2b1e69-7ae6-4d45-be99-0ac763011243","order_by":3,"name":"Oumaima Bouazizi","email":"","orcid":"","institution":"National Engineering School of Sfax: Ecole Nationale d'Ingenieurs de Sfax","correspondingAuthor":false,"prefix":"","firstName":"Oumaima","middleName":"","lastName":"Bouazizi","suffix":""},{"id":269174852,"identity":"63eb3967-14ce-44bf-9f01-0a6804320680","order_by":4,"name":"Radhia Gargouri-Bouzid","email":"","orcid":"","institution":"National Engineering School of Sfax: Ecole Nationale d'Ingenieurs de Sfax","correspondingAuthor":false,"prefix":"","firstName":"Radhia","middleName":"","lastName":"Gargouri-Bouzid","suffix":""},{"id":269174853,"identity":"376ce7e6-e904-48d8-9406-bf1a5a5bb5c1","order_by":5,"name":"Oumèma Nouri-Ellouz","email":"","orcid":"","institution":"University of Sfax Preparatory Engineering Institute of Sfax: Universite de Sfax Institut Preparatoire aux Etudes d'Engenieur de Sfax","correspondingAuthor":false,"prefix":"","firstName":"Oumèma","middleName":"","lastName":"Nouri-Ellouz","suffix":""}],"badges":[],"createdAt":"2024-01-21 07:33:01","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3883973/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3883973/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11540-024-09829-7","type":"published","date":"2024-11-25T15:57:10+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":50286296,"identity":"0ab9aa23-cebd-4b5d-bbd3-13ff5b09669d","added_by":"auto","created_at":"2024-01-29 06:50:56","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":962707,"visible":true,"origin":"","legend":"\u003cp\u003eMonitoring of the growth parameters during 40 days in Sp \u003cstrong\u003e(a)\u003c/strong\u003e and Cl plants \u003cstrong\u003e(b)\u003c/strong\u003e inoculated (+) or not (-) with \u003cem\u003eBacillus mojavensis \u003c/em\u003eI4 and subjected (SS) or not (C) to salt stress\u003c/p\u003e\n\u003cp\u003eValues are represented by means ± SD. Different letters (a, b, c and d) indicate significant difference between the different treatments (at \u003cem\u003eP \u0026lt; 0.05\u003c/em\u003e, ANOVA test)\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3883973/v1/ad6ed848299c10f22c21b4fb.png"},{"id":50286851,"identity":"62e797a4-08f9-44c9-b6df-5e7122682848","added_by":"auto","created_at":"2024-01-29 06:58:56","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":442369,"visible":true,"origin":"","legend":"\u003cp\u003eMonitoring of \u0026nbsp;fresh weight of stem, leaf and roots during 40 days in Sp \u003cstrong\u003e(a)\u003c/strong\u003e and Cl \u003cstrong\u003e(b)\u003c/strong\u003e \u0026nbsp;plants inoculated (+) or not (-) with \u003cem\u003eBacillus mojavensis \u003c/em\u003eI4 and subjected (SS) or not (C) to salt stress Values are represented by means ± SD. Different letters (a, b, c and d) indicate significant difference between the different treatments (at \u003cem\u003eP \u0026lt; 0.05\u003c/em\u003e, ANOVA test)\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3883973/v1/7c95b06e4460caae030a22f7.png"},{"id":50286303,"identity":"2091a0ef-408c-440c-aba6-7d947fd11b82","added_by":"auto","created_at":"2024-01-29 06:50:57","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":354503,"visible":true,"origin":"","legend":"\u003cp\u003eTotal chlorophyll content in leaves of the Sp \u003cstrong\u003e(a)\u003c/strong\u003e and Cl \u003cstrong\u003e(b)\u003c/strong\u003e plants inoculated (+) or not (-) with \u003cem\u003eBacillus mojavensis \u003c/em\u003eI4 and subjected (SS) or not (C) to salt stress\u003c/p\u003e\n\u003cp\u003eValues are represented by means ± SD. Different letters (a, b, c and d) indicate significant difference between the different treatments (at \u003cem\u003eP \u0026lt; 0.05\u003c/em\u003e, ANOVA test)\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3883973/v1/47650c12e32b39d0e4b88571.png"},{"id":50286300,"identity":"559c62d8-cf86-4720-b076-f5ded23393cd","added_by":"auto","created_at":"2024-01-29 06:50:57","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":289378,"visible":true,"origin":"","legend":"\u003cp\u003eAuxin \u003cstrong\u003e(A)\u003c/strong\u003eand proline \u003cstrong\u003e(B)\u003c/strong\u003e contents \u0026nbsp;in leaves and roots \u0026nbsp;of the Sp \u003cstrong\u003e(a)\u003c/strong\u003eand Cl \u003cstrong\u003e(b)\u003c/strong\u003e plants inoculated (+) or not (-) with \u003cem\u003eBacillus mojavensis \u003c/em\u003eI4 and subjected (SS) or not (C) to salt stress\u003c/p\u003e\n\u003cp\u003eValues are represented by means ± SD. Different letters (a, b, c and d) indicate significant difference between the different treatments (at \u003cem\u003eP \u0026lt; 0.05\u003c/em\u003e, ANOVA test)\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3883973/v1/196dce698a561291207ebe50.png"},{"id":50286299,"identity":"79375727-0a17-4fce-a3b8-e8d118a711ac","added_by":"auto","created_at":"2024-01-29 06:50:56","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":937455,"visible":true,"origin":"","legend":"\u003cp\u003eMDA \u003cstrong\u003e(A)\u003c/strong\u003e and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e \u003cstrong\u003e(B)\u003c/strong\u003e contents in leaves and roots of the Sp \u003cstrong\u003e(a)\u003c/strong\u003e and Cl \u003cstrong\u003e(b)\u003c/strong\u003e plants inoculated (+)\u0026nbsp; or not (-) with \u003cem\u003eBacillus mojavensis \u003c/em\u003eI4 and subjected (SS) or not (C) to salt stress\u003c/p\u003e\n\u003cp\u003eValues are represented by means ± SD. Different letters (a, b, c and d) indicate significant difference between the different treatments (at \u003cem\u003eP \u0026lt; 0.05\u003c/em\u003e, ANOVA test)\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3883973/v1/12bcd7870c8b40cf774dfa66.png"},{"id":50286301,"identity":"59abd408-6615-4ded-a3ae-3b3a38cc3d78","added_by":"auto","created_at":"2024-01-29 06:50:57","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":292098,"visible":true,"origin":"","legend":"\u003cp\u003eSOD \u003cstrong\u003e(A)\u003c/strong\u003e, GPX \u003cstrong\u003e(B)\u003c/strong\u003e and CAT \u003cstrong\u003e(C)\u003c/strong\u003eactivities in leaves and roots of the Sp \u003cstrong\u003e(a)\u003c/strong\u003eand Cl \u003cstrong\u003e(b)\u003c/strong\u003e plants inoculated (+) or not (-) with \u003cem\u003eBacillus mojavensis \u003c/em\u003eI4 and subjected (SS) or not (C) to salt stress\u003c/p\u003e\n\u003cp\u003eValues are represented by means ± SD. Different letters (a, b, c and d) indicate significant difference between the different treatments (at \u003cem\u003eP \u0026lt; 0.05\u003c/em\u003e, ANOVA test)\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3883973/v1/cff4c82a8e18ba9bfc0b81f6.png"},{"id":70382115,"identity":"17b9aef6-e3f2-475e-863f-78f03d2b15af","added_by":"auto","created_at":"2024-12-02 16:23:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4593375,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3883973/v1/1d6640ff-83df-45f2-b7ce-c58a9eb520ff.pdf"},{"id":50286852,"identity":"8152a568-4798-4159-bff5-5451c7e5b370","added_by":"auto","created_at":"2024-01-29 06:58:57","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":135953,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryFig.1.docx","url":"https://assets-eu.researchsquare.com/files/rs-3883973/v1/3d7d9fd97356efe4b0056ec1.docx"},{"id":50286297,"identity":"d7b2df23-96a6-4f95-b93e-6ace16370ba8","added_by":"auto","created_at":"2024-01-29 06:50:56","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":98095,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryFig.2.docx","url":"https://assets-eu.researchsquare.com/files/rs-3883973/v1/2150cbb3e3ceb162ac6d675c.docx"}],"financialInterests":"","formattedTitle":"Effect of the plant growth-promoting bacteria strain Bacillus mojavensis I4 on potato growth, physiology, tuber yield and quality under salt stress conditions","fulltext":[{"header":"Introduction","content":"\u003cp\u003eGlobal crop yield decreases by seventy percent due to environmental stresses (Neshat et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), among which salinity is frequent and considered the most devastating for the plants (Kesawat et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Aproximately 7% of land area and 33% of irrigated lands worldwide are affected by salinity (Chele et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). High soluble salt contents can alter soil fertility by causing retardation of plant growth and development (Abbas et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e ; Numan et al. 2019). Salt affects plants by interfering with many physiological and metabolic functions such as nitrogen fixation, ionic and water homeostasis, lipid metabolism, photosynthesis and protein synthesis (Li and Jian 2017; Hmaied et al. 2019). The accumulation of salt in the roots zone causes osmotic stress and disrupts cell ion homeostasis by inducing both the inhibition of essential elements uptake such as K\u003csup\u003e+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e and NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e and the accumulation of toxic elements such as Na\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e (Paranychianakis and Chartzoulakis \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Sodium is the most soluble and widespread element in salty soils. Its high accumulation in plants limits water conductance disturbs intracellular potassium influx and nutrient balance (Kumar et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The overproduction of reactive oxygen species (ROS) is the most frequent consequence of salt stress (Kesawatt et al. 2023). ROS (e.g. hydroxyl radical (HO\u003csup\u003e\u0026bull;\u003c/sup\u003e), superoxide radical (O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026bull; \u0026minus;\u003c/sup\u003e), single oxygen (O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e1\u003c/sup\u003e) and hydrogene peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e)) are highly reactive and at high amounts, noxious, leading to destrutive processes in cells (Kesawatt et al. 2023) restricting cell division and elongation (Egamberdieva et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Among vegetables, potato (\u003cem\u003eSolanum tuberosum\u003c/em\u003e L.) is the largest crop growing in 79% countries (FAO \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) ranked third after wheat and rice (FAO \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). However, this crop faces important challenges with salinity (Handayani et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), which affects negatively vegetative growth of plants leading to instability of tuberization and yielding through the inhibition of the formation and the swelling of tubers (Dahal et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). To ensure sustainable production under salt stress conditions, inoculation of plants with plant growth\u0026ndash;promoting bacteria (PGPB) has attracted attention as an alternative strategy, that is reliable method, ecologically mild and environnmenntally safe (Ali et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The inoculation with beneficial microorganisms may provide naturally drived solution to salinity and climate change by modulating crop development and preserving multiple associated ecosystems services (Liu et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The use of beneficial microbes such as PGPB in agriculture production systems started a long time ago and there is increasing evidence that it can enhance plant tolerance to adverse environmental stresses (Batool et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Some PGPB that cope with salinity (halotolerant strains), can be involved efficiently in physiological and biochemical pathways of plant response to salt stress (Abbas et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). PGPB can potentially alleviate environmental stress effects such as salinity at several stages of plant growth through a variety of mechanisms. These bacteria are known to produce the indole-3-acetic acid (IAA) auxin phytohormone. They provide minerals such as nitrogen, phosphate and potassium, siderophore production (Mishra et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2021\u003c/span\u003e ; Nashat et al. 2022 ; Cappellari et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). They can produce expolysaccharides (EPS) and volatile organic compounds (VOC) that play important role in plant protection.\u003c/p\u003e \u003cp\u003eIn this context, this study aims to investigate the effect of \u003cem\u003eBacillus mojavensis\u003c/em\u003e I4 (BmI4; Ghazala et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) PGPB on potato plant growth, tuber yield and quality under greenhouse culture conditions in the absence or presence of salt stress (100 mM NaCl). Morphological, physiological and biochemical parameters were monitored on Spunta (Sp) and Claustar (Cl) varieties. Plant growth and physiological parameters were measured during 40 days of culture. Moreover, we focused on the effect of PGPB on tuberization timing, tuber yield and quality under salt stress conditions. The antioxidant enzyme activities were followed since they are involved in control of ROS accumulation under stressful conditions. Superoxide dismutase (SOD), catalase (CAT) and peroxidase (GPX) are the main enzymes that play a major role in the self defense in plants (Mishra et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). SOD is the main antioxidant as it activates the first line of defense against ROS-induced damage by converting superoxide into hydrogen peroxide, followed by CAT and GPX degrading H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (Del Rio et al. 2018). The PGPB provide plants tolerance to stress by enhancing the activity of the antioxidant enzymes and other non-enzymatic antioxidants (Gururani et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2013\u003c/span\u003e ; Chatterjee et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e"},{"header":"Material and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003ePlant material\u003c/h2\u003e \u003cp\u003eThe study was carried out on two potato varieties Spunta (Sp), the most cultivated in Tunisia (80%; Azouz 1996) and also one of the most widely grown potatoes in the world (elornplants.com), and Claustar (Cl) variety. These plants were multiplied \u003cem\u003ein vitro\u003c/em\u003e on MS medium (Murashige and Skoog \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e1962\u003c/span\u003e) added with Morel vitamins (Morel and Wetmore \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1951\u003c/span\u003e) at a temperature varying from 22\u0026deg;C to 24\u0026deg;C and a photoperiod of 12h/days under a light intensity of 62 \u0026micro;E/m\u003csup\u003e2\u003c/sup\u003es.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eBacterial inoculum\u003c/h2\u003e \u003cp\u003ePlantlet roots were inoculated with \u003cem\u003eBacillus mojavensis\u003c/em\u003e I4 (BmI4) strain isolated from the soil of Sfax city in Tunisia and identified in the laboratory (accession number KF012872; Ghazala et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). This isolate was selected on the basis of its capacity to promote the growth of wheat plants by allowing the production of siderophores and IAA, as well as the fixation of nitrogen and the solubilization of phosphate. In addition, this strain tolerates a temperature of 55\u0026deg;C, 50 mg/l Cd and 10% NaCl (Ghazala et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), making it an excellent candidate for mitigating the effect of saline stress on plants. The BmI4 strain was cultivated on LB broth medium at 37\u0026deg;C and maintained at 4\u0026deg;C before use.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003ePlant inoculation, cultivation and application of salt stress\u003c/h2\u003e \u003cp\u003ePlantlets of the two potato varieties, approximately three weeks-old and sufficiently rooted in MS medium, were inoculated by soaking their roots for 20 min in the BmI4 strain suspension (10\u003csup\u003e6\u003c/sup\u003e cfu/ml) previously prepared in PBS buffer (137 mM NaCl, 2.7 mM KCl, 8 mM Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e, and 2 mM KH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e) for 20 min. Control plantlets which had the same age and length were treated with PBS buffer. These inoculated and non-inoculated plantlets (control) were transferred in plastic pots (12 cm in diameter) containing an autoclaved mixture of 50% sand and 50% peat (Potgrond H: Klasmann Deilmann, Geeste, Germany), and watered with tap water at a rate of 50 ml/pot twice a week. After 15 days of greenhouse acclimatization, the inoculated and non-inoculated plant groups were each divided into two groups to study the response to salt stress. Thus, the plants of each potato variety were arranged in 4 batches which underwent different treatments:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eNon-inoculated plants not subjected to salinity (control: C\u003csup\u003e-\u003c/sup\u003e)\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eInoculated plants not subjected to salinity (C\u003csup\u003e+\u003c/sup\u003e)\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eNon-inoculated plants subjected to salinity (SS\u003csup\u003e-\u003c/sup\u003e)\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eInoculated plants subjected to salinity (SS\u003csup\u003e+\u003c/sup\u003e)\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eTo apply salt stress in batches (2) and (4), the plants were irrigated with 50 ml salt solution (100 mM NaCl) twice a week the 15 days of the acclimatization until the cycle end. Whereas plants of batches (1) and (3) were kept watered with tap water. Plant culture was conducted between March 11and May 25 (2023), in a greenhouse in the presence of sunlight.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003ePlant growth parameters\u003c/h2\u003e \u003cp\u003ePlant growth was evaluated for 40 days from the beginning of the treatment by measuring stem length and diameter, leaf number and area on seven plants previously selected from each batch. The tuber yield (g/plant) was also determined on these plants at the end of the cycle (60 days). At 10, 25 and 40 days of treatment, seven plants were used to measure each of leaf, stem and root fresh weights, physiological parameters and tuber weight.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of chlorophyll contents\u003c/h2\u003e \u003cp\u003eTotal chlorophyll was extracted from fresh leaves (0.01g) ground in acetone (Arnon. 1949). After centrifugation at 12000 rpm for 15 min, the supernatant containing the pigments was collected and the absorbance of the samples was determined at 645 nm and 663 nm. The content of chlorophylls a (Chl a), b (Chl b) and total chlorophyll (Chl t) were determined according to the following formulas:\u003c/p\u003e \u003cp\u003eChl a (\u0026micro;g/g FW) = [12.7* A663\u0026thinsp;\u0026minus;\u0026thinsp;2.69 *A645]*V/FW\u003c/p\u003e \u003cp\u003eChl b (\u0026micro;g/g FW) = [22.9* A645\u0026thinsp;\u0026minus;\u0026thinsp;4.68 *A663]*V/FW\u003c/p\u003e \u003cp\u003eChl t (\u0026micro;g∕g FW)\u0026thinsp;=\u0026thinsp;Chl a\u0026thinsp;+\u0026thinsp;Chl b\u003c/p\u003e \u003cp\u003ewith FW: fresh weight of leaves; V: volume of sample\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003eDetrermination of malondialdehyde (MDA) content\u003c/h2\u003e \u003cp\u003eLipid peroxidation was determined as thiobarbituric acid (TBA) reactive metabolites mainly MDA in leaves and roots as described by Hodges et al (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). The fresh leaves and roots (0.15 g) were homogenized in 1.5 ml of trichloroacetic acid (TCA) 0.1%. After centrifugation at 12000 rpm for 30 min at 4\u0026deg;C, the supernatant was mixed with 2 ml of TBA/TCA solution (0.8% TBA and 15% TCA dissolved in 0.25 N HCl). The mixture was heated at 100\u0026deg;C for 15 min and then centrifuged at 12000 rpm for 10 min. The amont of MDA was measured spectrophotometrically at 532 and 600 nm, calculated using a standard curve and expressed as nmol/g FW.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003eDetermination of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e levels\u003c/h2\u003e \u003cp\u003eThe H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e content in leaves and roots was determined according to Lereto and Velikova (2001) method. The fresh leaves and roots (0.1 g) were ground in the presence of 2 ml TCA 0.1%. The extracts were centrifuged at 12000 rpm for 15 min. An aliquot of 0.5 ml of the supernatant was supplemented with 0.5 ml of potassium phosphate buffer (10 mM K\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e, 10 mM KH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, pH 7) and 1 ml of KI (1 M). The absorbance was measured at 390 nm and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e content was calculated using a standard curve and expressed as \u0026micro;mol/g FW.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of protein extract\u003c/h2\u003e \u003cp\u003eThe fresh leaves and roots (0.1 g) were ground in a mortar with 1ml Tris HCl buffer (67 mM, pH 8). After centrifugation at 12000 rpm at 4\u0026deg;C 30 min, the supernatant was used to assess SOD, GPX and CAT activities (Kammoun et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Protein concentration in the extract was determined using the Bradford method (Kruger 1994).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of SOD activity\u003c/h2\u003e \u003cp\u003eThe superoxide dismutase (SOD) activity was determined by monitoring the inhibition of the photo-reduction of Nitro Blue Tetrazolium (NBT) (Dhindsa et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1981\u003c/span\u003e). The reaction mix contained 50 mM phosphate buffer (pH 7), 2.64 mM NBT, 0.26 mM riboflavin and Na\u003csub\u003e2\u003c/sub\u003eEDTA-methionine. The photo-reduction of NBT was measured at 560 nm and the SOD activity was expressed as units per milligram of protein. The amount of SOD inhibiting the reaction rate by 50% was defined as one SOD unit.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of CAT activity\u003c/h2\u003e \u003cp\u003eThe CAT activity was assayed by following the consumption of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e at 240 nm (Aebi \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1984\u003c/span\u003e). The reaction mix contained 100 \u0026micro;l of protein extract in 1880 \u0026micro;l of 0.1 M phosphate buffer supplemented with 100 \u0026micro;l H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (10 mM) (Jbir-koubaa et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). One unit of catalase activity was defined as the amount that decomposes one \u0026micro;mol of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of GPX activity\u003c/h2\u003e \u003cp\u003eThe GPX activity was measured as described by Floh and Gunzler (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1984\u003c/span\u003e). Indeed, 200 \u0026micro;l of enzyme extract were mixed with 400 \u0026micro;L of glutathione (GSH) solution 0.1 mM and 200 \u0026micro;l of phosphate buffer (67 mM, pH 7.8). The mixture was incubated at 25\u0026deg;C for 5 min, then 200 \u0026micro;L of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (1.3 mM) were added and incubation pursued for 10 min. The reaction mixture was then supplemented with 1 ml TCA (1%). After centrifugation at 3000 rpm for 10 min at 4\u0026deg;C, 480 \u0026micro;l of the supernatant was mixed with 2.2 ml of Na\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e (0.32 M) and 320 \u0026micro;l of 5,5\u0026rsquo;-dithio-bis-(2-nitrobenzoic acid) (DTNB) (10 mM). The oxidized glutathione (GSSG) produced was determined by measuring the absorbance at 412 nm (Kammoun et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The GPX activity was calculated as follows:\u003c/p\u003e \u003cp\u003e\u0026micro;mol\u003csub\u003ereduced\u003c/sub\u003eGSH \u003csub\u003edisappeared /min/mg of protein\u003c/sub\u003e = [(OD sample-OD control/OD control)*(0.04*5/X*10)]\u003c/p\u003e \u003cp\u003ewith X : protein concentration (mg/ml) ; 0.04 : initial quantity of reduced GSH ; 5: to move from activity in 200 mL to activity in 1 ml; 10 : reaction time\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of auxin concentration\u003c/h2\u003e \u003cp\u003eThe fresh leaves and roots (0.1g) were homogenized in 1 ml of ethanol. After centrifugation at 12000 rpm for 30 min at 4\u0026deg;C, the supernatant was mixed with 2 ml of Salkowki\u0026rsquo;s reagent. The absorbance was measured at 530 nm. The auxin content was determined using a standard curve of IAA and expressed as \u0026micro;g/g FW (Ghazala et al, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of proline content\u003c/h2\u003e \u003cp\u003eProline content was measured according to Bates et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1973\u003c/span\u003e). The fresh mass (0.1g) from leaves and roots was ground in 4 ml sulfosalicylic acid (3%) and centrifuged at 10000 rpm for 30 min. The supernatant was then mixed with 1 ml glacial acetic acid and 1 ml ninhydric acid. After incubation at 100\u0026deg;C for 1 h, 2 ml of toluene were added. The absorbance of upper phase was measured at 520 nm. The proline amount was calculated from a standard curve and expressed as mmol/g FW.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of tuber yield, number, caliber, eyes number and skin color\u003c/h2\u003e \u003cp\u003eTubers of Sp plants grown under the different conditions were collected and weighted. The tuber yield (g/plant) was determined during the 40 days of monitoring and at the end of the cycle (60 days). Tuber number and caliber as well as number of eyes were determined on tubers harvested at the final step. The skin color of these tubers was also measured using a Chroma Meter CR-400/410 colorimeter (Konica Minolta). Three orthogonal coordinates define this parameter: the clarity index L* and the chromatic coordinates a* (red) and b* (yellow). They were determined by scanning the potato skin at five locations.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of dry matter\u003c/h2\u003e \u003cp\u003eThe percentage of tuber dry matter of tubers was determined after drying for 72 h at 80\u0026deg;C. Dry matter content was determined using the following formulae: DW \u0026times; 100/FW with FW : fresh weight; DW : dry weight\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eChemical analysis of tubers\u003c/h2\u003e \u003cp\u003eLipid, total nitrogen and ash contents of potato tubers were determined according to the American Association of Cereal Chemists 2000 standard methods 46\u0026thinsp;\u0026minus;\u0026thinsp;30, 30\u0026thinsp;\u0026minus;\u0026thinsp;10 and 08\u0026thinsp;\u0026minus;\u0026thinsp;01 respectively (Ben Jeddou et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The starch content was determined using the enzymatic colorimetric method described by Khabou et al. (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). Reducing sugar content was determined by the acid 3, 5-dinitrosalicylic (DNS) method as described by Miller (\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e1959\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eCarotenoids content of tubers\u003c/h2\u003e \u003cp\u003eTo extract lipophilic compounds, 0.3 g of fresh tuber mass were ground in liquid nitrogen and then homogenized for 30 min at 4\u0026deg;C in 1.5 ml of acetone. After centrifugation at 10,000 rpm for 10 min at 4\u0026deg;C, the supernatant was collected, and the pellet was re-extracted with the same solvent. The two supernatants were pooled, and the total carotenoid concentration was determined by measuring the absorbance at 450 nm and expressed as \u0026micro;g/g FW (Chiab et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2023\u003c/span\u003e)\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eAll data were presented as the means\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD) of three independent biological replicates. The comparison between the different values were statistically effectuated by one-way ANOVA test using IBM SPSS Statistics (version 20). Differences were considered significant at P\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eEffect of inoculation on growth and morphology\u003c/h2\u003e \u003cp\u003eThe influence of BmI4 strain inoculation on the growth of Sp and Cl plants under greenhouse culture was evaluated under both saline (100 mM NaCl) and standard (0 mM NaCl) conditions by measuring the number, area and fresh weight (FW) of leaves, the elongation, diameter and FW of stems as well as the FW of roots during 40 days. Salinity affected all growth parameters (SS\u003csup\u003e\u0026minus;\u003c/sup\u003e) (Supplementary Fig.\u0026nbsp;1; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e,\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The effect of BmI4 strain seems to be more pronounced on the Sp variety, mitigating the effects of salt stress compared to the Cl variety which exhibited very little differences between inoculated and non-inoculated plants. Indeed, the inoculation with BmI4 enhanced stem growth in Sp variety submitted to salt stress for which FW was similar to that of control plants (non-inoculated and grown under standard conditions, C\u003csup\u003e\u0026minus;\u003c/sup\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In addition, stem diameter of the inoculated Sp plants submitted to salt stress (SS\u003csup\u003e+\u003c/sup\u003e) seems to be slightly larger than that of control plants (C\u003csup\u003e\u0026minus;\u003c/sup\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In contrast, the BmI4 inoculation did not lead to any significant change of stem elongation in the presence of salt stress. Although salinity reduced leaf growth, it remained equivalent (FW and area of leaves) or even better (number of leaves) in the inoculated than in the control plants of the Sp variety. In addition, BmI4 boosted roots FW of Sp. These results indicate that roots inoculation with BmI4 strain led to more vigorous plants from Sp variety. For Cl variety, most growth parameters in inoculated plants were close to those of non-inoculated plants in the presence of salt stress, well below those in control.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003eChlorophyll content\u003c/h2\u003e \u003cp\u003eDue to its crucial role in photosynthesis, the total chlorophyll content was determined in the leaves of the plants subjected to the different treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). A significant increase of chlorophyll content was observed in Sp plants inoculated with BmI4 and subjected to salt stress. However, in the Cl variety, no significant differences were noticed in chlorophyll contents under the different conditions after 25 days of treatment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003eAuxin content\u003c/h2\u003e \u003cp\u003eTo better understand the effect of inoculation by BmI4 on Sp and Cl mitigation of salinity effect, the auxins content was measured in leaves and roots of inoculated and non-inoculated plants subjected or not to salinity. The results (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA) showed that auxins were more accumulated in roots than in leaves. Moreover, the inoculation with BmI4 led to higher auxins accumulation in Sp after 10 days of culture under salt stress conditions. These results might explain the enhanced growth observed in these inoculated plants.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec25\" class=\"Section3\"\u003e \u003ch2\u003eProline content\u003c/h2\u003e \u003cp\u003eOsmotic adjustment is one of the essential mechanisms for the adaptation of plants to saline stress. It can be ensured by the accumulation of compatible solutes in the cells, such as proline. An important increase of proline contents was noticed in leaves of Spunta after 25 days of stress conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). This increase was more important in inoculated plants. In contrast, low proline amounts were measured in Cl variety during the 40 days of culture for the different treatments. These data suggest that inoculation of plants with BmI4 helps the Sp plants capacity to alleviate salt stress negative effects through the enhancement of proline synthesis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section3\"\u003e \u003ch2\u003eEffect of inoculation on the oxidative stress parameters\u003c/h2\u003e \u003cp\u003eAmong the response parameters to abiotic stress, we considered the accumulation of ROS. Therefore, the MDA and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e contents were assessed in the roots and leaves of inoculated and non-inoculated plants grown in the presence or absence of salt stress at 10, 25 and 40 days. MDA contents remained at low levels in roots of both Sp and Cl plants for all treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA). Salt stress conditions caused MDA increase in plant leaves, while inoculation with BmI4 led to a decrease of MDA levels. Indeed, inoculated plants of both genotypes submitted to salinity exhibited MDA content closed to that of respective control plants and even below in Sp leaves at 40 days. Similarly, almost no significant H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e increase was observed in inoculated plant leaves and roots upon the application of salt stress (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB). However, the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e content reached the highest level in non-inoculated plants, and it increased with duration of stress.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec27\" class=\"Section3\"\u003e \u003ch2\u003eEffect of inoculation on the antioxidant enzyme activities\u003c/h2\u003e \u003cp\u003eIn order to better understand the plant response, the antioxidant enzymes SOD, CAT and GPX activities were checked in the roots and leaves of both Sp and Cl plants submitted to the different treatments at 10, 25 and 40 days.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec28\" class=\"Section2\"\u003e \u003ch2\u003eSOD activity\u003c/h2\u003e \u003cp\u003eThe inoculation of Sp plants with BmI4 resulted in the increase of SOD activity in leaves at 10 days of salt treatment and later on this activity became comparable to that of plants grown in the different conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA). This result can be related to low MDA accumulation. In addition, the SOD activity was stimulated in inoculated Sp roots under salt stress conditions at 25 days and 40 days, whereas in non-inoculated Sp it remained low and close to control (C\u003csup\u003e\u0026minus;\u003c/sup\u003e). The leaves of treated Cl plants did not show any increase of SOD activity compared to the respective control plants. However, an increase in SOD activity was measured in the roots of inoculated Cl plants grown under the standard conditions. The low enzyme induction in the roots of BmI4 treated Cl under stress conditions may be explained by the low MDA levels.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec29\" class=\"Section2\"\u003e \u003ch2\u003eGPX and CAT activities\u003c/h2\u003e \u003cp\u003eThe GPX and CAT activities increased in both leaves and roots of inoculated Sp plants submitted to salt stress compared to control plants (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB,C). The GPX activity increased with duration of stress while the highest CAT activity increase was noticed after 10 days of salt stress. The GPX and CAT enhancement in Sp may be associated to the low H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e content. However, in non-inoculated Sp leaves and roots, these activities increased after 25 days of salt stress, they decreased at 40 days of stress which may explain the significant accumulation of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e during the treatment. In the Cl leaves, inoculation with BmI4 seems to enhance GPX activity at 40 days (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB), whereas it remained at very low levels in non-inoculated leaves under salt stress conditions. The CAT activity remained low in Cl plants treated with NaCl (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eC) in inoculated and non-inoculated plants. This can be related to H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e amount measured.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eEvaluation of tuber yield and quality\u003c/h3\u003e\n\u003cp\u003eTuber yield (g/plant) was determined during the culture period (11 March-25 May 2023) for Sp variety since Cl plants were not able to tuberize at this season (Supplementary Fig. 2). Inoculation of plants with BmI4 strain allowed earlier tuber initiation and better yield (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eA). Indeed, after 25 days of culture, tuber development was initiated, whereas only slight swellings in some stolon tips were found on non-inoculated plants. This earlier induction of tuber formation was associated with higher growth rate and final tuber biomass production (60 days). BmI4 inoculation resulted in a gain of final tuber yield under salt stress conditions. The tuber yield of BmI4 inoculated plants submitted to salinity was close to the control (C\u003csup\u003e\u0026minus;\u003c/sup\u003e) at the end of culture period (60 days). Similarly the number of tuber per plant of inoculated plants was higher than that of non-inoculated ones either in the presence (3.083\u0026thinsp;\u0026plusmn;\u0026thinsp;0.135 in inoculated plants vs 1.75\u0026thinsp;\u0026plusmn;\u0026thinsp;0.048 in non-inoculated plants) or in the absence (3.833\u0026thinsp;\u0026plusmn;\u0026thinsp;0.021 vs 2.167\u0026thinsp;\u0026plusmn;\u0026thinsp;0.895) of salt stress. Moreover, the higher caliber of tubers were obtained in inoculated plants and higher number of eyes than non-inoculated plants in both culture conditions (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eB). All these data confirm that BmI4 inoculation enhanced capacity of multiplication in Sp. With regards to tuber skin color (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eB), it seems that salt stress conditions resulted in a decrease of the clarity (L*) and a reduction of yellow color (b*) while the red color (a*) increased. In contrast, the inoculation with BmI4 modulated the clarity by recovery of b* value and increase of a* under salt stress conditions.\u003c/p\u003e\n\u003cdiv id=\"Sec31\" class=\"Section2\"\u003e\n \u003ch2\u003eEffect of inoculation on tuber composition\u003c/h2\u003e\n \u003cp\u003eThe tuber composition i.e. dry matter, ashes, starch, reducing sugars, lipid, protein, nitrogen and carotenoid contents was analyzed in relation to the different plant treatments. We noticed that inoculation with BmI4 led to an increase of dry matter, starch, ash, protein and carotenoid contents of tubers (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). However, salinity affected negatively dry matter, starch and ash contents. The starch and ash content in tubers from inoculated plants submitted to salinity reached levels well above control. Lipid content remained low in all potatoes but total proteins and nitrogen increased significantly with inoculation under salt stress conditions compared to control (C\u003csup\u003e\u0026minus;\u003c/sup\u003e). The lowest level of reducing sugars was recorded in tubers obtained from inoculated plants grown in the presence of salt. Tuber carotenoids increased in the different treatments compared to control, the highest percentage was recorded in tubers obtained from inoculated plants subjected to salinity.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e : \u003cstrong\u003eA\u003c/strong\u003e. Tuber kinetic production (g/plant) of Spunta plants inoculated (+) \u0026nbsp;or not (-) with \u003cem\u003eBacillus mojavensis\u003c/em\u003e I4 and subjected (SS) or not (C) to salt stress\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eB\u003c/strong\u003e. Mean number of eyes, caliber and skin color of Spunta tubers of harvested at the end of culture (60d) \u0026nbsp;from \u0026nbsp; plants inoculated (+) \u0026nbsp;or not (-) with \u003cem\u003eBacillus mojavensis\u003c/em\u003e I4 and subjected (SS) or not (C) to salt stress\u003c/p\u003e\n \u003cp\u003eValues are represented by means \u0026plusmn; SD. Different letters (a, b, c and d) indicate significant difference between the different treatments (at \u003cem\u003eP \u0026lt; 0.05\u003c/em\u003e, ANOVA test)\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eA\u003c/strong\u003e\u003c/p\u003e\n \u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"527\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"10.076045627376425%\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"14.638783269961976%\"\u003e\n \u003cp\u003e10d\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.376425855513308%\"\u003e\n \u003cp\u003e25d\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.38403041825095%\"\u003e\n \u003cp\u003e40d\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.524714828897338%\"\u003e\n \u003cp\u003e60d\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"10.076045627376425%\"\u003e\n \u003cp\u003eC\u003csup\u003e\u0026nbsp;-\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.638783269961976%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.376425855513308%\"\u003e\n \u003cp\u003e0\u003csup\u003eC\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.38403041825095%\"\u003e\n \u003cp\u003e0.888\u003csup\u003ec\u0026nbsp;\u003c/sup\u003e\u0026plusmn; 0.065\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.524714828897338%\"\u003e\n \u003cp\u003e1.917\u003csup\u003eb\u003c/sup\u003e \u0026plusmn; 0.086\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"10.076045627376425%\"\u003e\n \u003cp\u003eSS\u003csup\u003e-\u0026nbsp;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.638783269961976%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.376425855513308%\"\u003e\n \u003cp\u003e0\u003csup\u003eC\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.38403041825095%\"\u003e\n \u003cp\u003e0.502\u003csup\u003ed\u003c/sup\u003e \u0026plusmn; 0.036\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.524714828897338%\"\u003e\n \u003cp\u003e0.527\u003csup\u003ed\u003c/sup\u003e \u0026plusmn; 0.032\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"10.076045627376425%\"\u003e\n \u003cp\u003eC\u003csup\u003e+\u0026nbsp;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.638783269961976%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.376425855513308%\"\u003e\n \u003cp\u003e0.735\u003csup\u003ea\u003c/sup\u003e \u0026plusmn; 0.037\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.38403041825095%\"\u003e\n \u003cp\u003e3.377\u003csup\u003ea\u003c/sup\u003e \u0026plusmn; 0.296\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.524714828897338%\"\u003e\n \u003cp\u003e4.975\u003csup\u003ea\u003c/sup\u003e \u0026plusmn; \u0026nbsp;0.267\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"10.076045627376425%\"\u003e\n \u003cp\u003eSS\u003csup\u003e\u0026nbsp;+\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.638783269961976%\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.376425855513308%\"\u003e\n \u003cp\u003e0.347\u003csup\u003eb\u003c/sup\u003e \u0026plusmn; 0.012\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.38403041825095%\"\u003e\n \u003cp\u003e1.767\u003csup\u003eb\u003c/sup\u003e \u0026plusmn; 0.007\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.524714828897338%\"\u003e\n \u003cp\u003e1.799\u003csup\u003ec\u003c/sup\u003e \u0026plusmn; 0.069\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\u003cbr\u003e\u003cstrong\u003eB\u003c/strong\u003e\u003cbr\u003e\n \u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"688\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"20.203488372093023%\" colspan=\"2\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"9.30232558139535%\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"17.00581395348837%\"\u003e\n \u003cp\u003eC\u003csup\u003e-\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.86046511627907%\" colspan=\"2\"\u003e\n \u003cp\u003eSS\u003csup\u003e-\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.86046511627907%\"\u003e\n \u003cp\u003eC\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.767441860465116%\"\u003e\n \u003cp\u003eSS\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"29.50581395348837%\" colspan=\"3\" valign=\"bottom\"\u003e\n \u003cp\u003eMean number\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;of eyes\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.6046511627907%\" colspan=\"2\"\u003e\n \u003cp\u003e6\u003csup\u003eb\u003c/sup\u003e \u0026plusmn; 0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.261627906976743%\"\u003e\n \u003cp\u003e3,20\u003csup\u003ed\u003c/sup\u003e \u0026plusmn; 0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.86046511627907%\"\u003e\n \u003cp\u003e8.20\u003csup\u003ea\u003c/sup\u003e \u0026plusmn; 0.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.767441860465116%\"\u003e\n \u003cp\u003e4.80\u003csup\u003ec\u003c/sup\u003e \u0026plusmn; 0.740\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"17.587209302325583%\" rowspan=\"2\" valign=\"bottom\"\u003e\n \u003cp\u003eCaliber(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.918604651162791%\" colspan=\"2\" valign=\"bottom\"\u003e\n \u003cp\u003e\u0026lt;1.5 cm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.6046511627907%\" colspan=\"2\"\u003e\n \u003cp\u003e17.63\u003csup\u003ec\u003c/sup\u003e\u0026plusmn; 0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.261627906976743%\"\u003e\n \u003cp\u003e75.13\u003csup\u003ea\u003c/sup\u003e \u0026plusmn; 0.100\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.86046511627907%\"\u003e\n \u003cp\u003e0\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.767441860465116%\"\u003e\n \u003cp\u003e54,04\u003csup\u003eb\u003c/sup\u003e \u0026plusmn; 0.010\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.462081128747796%\" colspan=\"2\" valign=\"bottom\"\u003e\n \u003cp\u003e[1.5-3cm]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.57495590828924%\" colspan=\"2\"\u003e\n \u003cp\u003e82.35\u003csup\u003eb\u003c/sup\u003e \u0026plusmn; 0.010\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.51851851851852%\"\u003e\n \u003cp\u003e25.1\u003csup\u003ed\u003c/sup\u003e \u0026plusmn; 0.010\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.458553791887127%\"\u003e\n \u003cp\u003e100\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.98589065255732%\"\u003e\n \u003cp\u003e45,92\u003csup\u003ec\u003c/sup\u003e \u0026plusmn; 0.025\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"17.587209302325583%\" valign=\"bottom\"\u003e\n \u003cp\u003eSkin color\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.918604651162791%\" colspan=\"2\" valign=\"bottom\"\u003e\n \u003cp\u003eL*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.6046511627907%\" colspan=\"2\"\u003e\n \u003cp\u003e72.51\u003csup\u003eb\u003c/sup\u003e \u0026plusmn; 0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.261627906976743%\"\u003e\n \u003cp\u003e44.95\u003csup\u003ed\u003c/sup\u003e \u0026plusmn; 0.050\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.86046511627907%\"\u003e\n \u003cp\u003e77.34\u003csup\u003ea\u003c/sup\u003e \u0026plusmn; 0.010\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.767441860465116%\"\u003e\n \u003cp\u003e62.5\u003csup\u003ec\u003c/sup\u003e \u0026plusmn; 0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"17.587209302325583%\" valign=\"bottom\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"11.918604651162791%\" colspan=\"2\" valign=\"bottom\"\u003e\n \u003cp\u003ea*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.6046511627907%\" colspan=\"2\"\u003e\n \u003cp\u003e3.77\u003csup\u003ec\u003c/sup\u003e \u0026plusmn; 0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.261627906976743%\"\u003e\n \u003cp\u003e6.32\u003csup\u003eb\u003c/sup\u003e \u0026plusmn; 0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.86046511627907%\"\u003e\n \u003cp\u003e2.98\u003csup\u003ed\u003c/sup\u003e\u0026nbsp; \u0026plusmn; 0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.767441860465116%\"\u003e\n \u003cp\u003e7.12\u003csup\u003ea\u003c/sup\u003e \u0026plusmn; 0.015\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"17.587209302325583%\" valign=\"bottom\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"11.918604651162791%\" colspan=\"2\" valign=\"bottom\"\u003e\n \u003cp\u003eb*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.6046511627907%\" colspan=\"2\"\u003e\n \u003cp\u003e36.34\u003csup\u003ec\u003c/sup\u003e\u0026nbsp; \u0026plusmn; 0.040\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.261627906976743%\"\u003e\n \u003cp\u003e24.26\u003csup\u003ed\u003c/sup\u003e \u0026plusmn; 0.040\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.86046511627907%\"\u003e\n \u003cp\u003e37.47\u003csup\u003ea\u003c/sup\u003e \u0026plusmn; 0.010\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.767441860465116%\"\u003e\n \u003cp\u003e36.53\u003csup\u003eb\u003c/sup\u003e \u0026plusmn; 0.038\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cstrong\u003eTable 2\u003c/strong\u003e : Chemical composition of \u0026nbsp;tubers of final yield (60 days) obtained from Spunta plants inoculated (+) \u0026nbsp;or not (-) with\u0026nbsp;\u003cem\u003eBacillus mojavensis\u003c/em\u003e I4\u0026nbsp;and subjected (SS) or not (C) to sat stress\u003c/p\u003e\n \u003cp\u003eValues are represented by means \u0026plusmn; SD. Different letters (a, b, c and d) indicate significant difference between the different treatments (at \u003cem\u003eP \u0026lt; 0.05\u003c/em\u003e, ANOVA test)\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003ctable id=\"Taba\" border=\"1\"\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eC\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSS\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eC\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003eSS\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDry matter (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22.05\u003csup\u003eb\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.040\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12.59\u003csup\u003ed\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e24.66\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.065\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e19.15\u003csup\u003ec\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.035\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAshes (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.43\u003csup\u003ec\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.002\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.74\u003csup\u003ed\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.007\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e1.7\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.050\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.6\u003csup\u003eb\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStarch (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.62\u003csup\u003ec\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.42\u003csup\u003ed\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e20.02\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e17.02\u003csup\u003eb\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.016\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eReducing sugars (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.36\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.007\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.30\u003csup\u003ec\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e0.35\u003csup\u003eb\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.008\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.25\u003csup\u003ed\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.040\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLipids (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.440\u003csup\u003ec\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.94\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e0.29\u003csup\u003ed\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.004\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.56\u003csup\u003eb\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.010\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTotal proteins (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.9\u003csup\u003ec\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.050\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.53\u003csup\u003ed\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e7.49\u003csup\u003eb\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.21\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.080\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTotal nitrogen (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.94\u003csup\u003ec\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.008\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.88\u003csup\u003ed\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.013\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e1.19\u003csup\u003eb\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.002\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.313\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.013\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCarotenoids (\u0026micro;g/g FW)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.56\u003csup\u003ec\u003c/sup\u003e \u0026plusmn; 0.150\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.2\u003csup\u003eb\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.030\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\"\u003e\n \u003cp\u003e3.25\u003csup\u003eb\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.010\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.35\u003csup\u003ea\u003c/sup\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.080\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe increase of food demand with the rise of global population needs the development of sustainable agriculture to improve yields and quality of crops especially under salt stress conditions. Indeed, salt stress is one of the rapidly growing environmental stress over the world (Abbas et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The use of PGPB in agricultural practices is a viable solution to garantee food demand (Mehmood et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In the present study, we focused on the effect of the PGPB strain BmI4 inoculation on Sp and Cl potatoes grown under salt stress (100 mM) in the greenhouse. Growth monitoring was carried out by following different traits including stem elongation and diameter, leaf number and area and organ fresh weight. The overall morphologly proved that inoculation with BmI4 strain stimulated growth allowing alleviation of salt stress devastating effect, especially in Sp variety. While salt stress did not lead to any significant decrease of chlorophyll pigments especially in Sp leaves, the inoculation with the BmI4 strain improved significantly total chlorophyll content in Sp plants under saline conditions, might helpful in explaining their better growth. This result further confirm that beneficial bacteria treatment can have positive effect on photosynthetic activity and chlorophyll content (Efthimiadou et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Similarly, Ghazala et al. (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) showed that the chlorophyll increased in salt acclimated wheat treated by BmI4 that suggests photosynthesis enhancement. We also noticed a stability in chlorophyll content with duration of stress (40 days) suggesting that BmI4 inoculation improved plant adaptation to salt stress. Similarly sweet peppers treated with \u003cem\u003eBacillus thuringiensis\u003c/em\u003e MH161336 indicated positive correlation between chlorophyll content and inoculum size (AlKahtani et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Since, salinity affects tuber formation and bulking due to high salt accumulation in tuber cells, resulting in altered osmotic potential and nutrient uptake capacity (Dahal et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) we evaluated the tuber production capacity of plants under the different culture conditions. Our results showed that BmI4 inoculation allowed higher tuber yield (60 days) in terms of tuber weight and number under control and salinity conditions. Moreover, the higher eyes number on these potatoes may reflect their higher potential for further multiplication. Our results are in agreement with other studies demonstrating the efficiency of \u003cem\u003eBacillus\u003c/em\u003e sp. strains to stimilate the salt stress adaptation in different plant species (Peng et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Lee et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Patani et al. \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Ghazala et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2023\u003c/span\u003e ; \u0026Ouml;zt\u0026uuml;rk and Dursun \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Likewise, Gururani et al. (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) repported that the use of \u003cem\u003eBacillus\u003c/em\u003e sp. allowed enhancement of potato plant growth. Nookaraju et al. (\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) reported the positive influence of these strains on \u003cem\u003ein vitro\u003c/em\u003e tuberization. Tahir et al. (\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) revealed that the use of consortium of \u003cem\u003eBacillus\u003c/em\u003e strains increased biomass of potato plant by almost 76% and tuber weight by 84% in saline conditions. In our case, tuber yield per plant (g/plant) increased by 241.3% and tuber weight by 93.6% with the BmI4 inoculation of plants under salinity conditions. The BmI4 inoculation of Sp plants seems to increase precocity of tuberization at 25 days whereas no tubers were found in non-inoculated plants. The observed increase of leaf growth and development in inoculated plants may be correlated with the earliness time of tuber initiation (Odgerel K and B\u0026aacute;nfalvi Z \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Early tuberization was also reported in potato plants inoculated by PGPB by Oswald et al (2011). These authors attributed the increased tuber yields in PGPB treated plants to early tuber induction, leaf area development and increase of photosynthetic rates. Under salinity conditions, the auxin production of BmI4 inoculated plants increased in comparison to the non-inoculated ones. Since BmI4 strain is able to produce IAA (Ghazala et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), it could be the one source of this increasing auxin content which can be related to the better growth and yield. Tahir et al (\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) showed an increase of indole-compounds in root exsudates of potato plants inoculated with PGPR \u003cem\u003eBacillus\u003c/em\u003e strains as compared to the other treatment under normal and salt affected soil conditions. In addition, these authors demonstrated a correlation between auxins and tuber production. Kolachevskaya et al. (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) reported that endogenous auxin confirmed their role in tuber enlargement induction and growth. These processes were tightly linked with a sharp rise of the auxin level in the subapical zone of stolons that were generating tubers. At 25 days, the increase of auxin in inoculated Sp plants was associated with improvement of plant growth and tuber production. However, no tuber formation was observed in non-inoculated plants. In Cl variety, the increase of auxin content in inoculated plants under salinity was correlated with a slight improvement of plant growth. Plant tissue injury generates excess of MDA that can lead to damaging several macromolecules (Juan et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and MDA contents were monitored in the Sp and Cl plants submitted to the different treatments. Results indicate that H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and MDA contents were lower in inoculated plants of both genotypes compared to non-inoculated ones in the presence of salinity. This indicates that BmI4 inoculated plants exhibited better capacity to cope with salinity than control ones. Indeed, in Sp inoculated with BmI4, the SOD, CAT and GPX showed significant increase in comparison to non-inoculated plants explaining the decrease of MDA and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e contents. However, these enzyme activities did not seem to increase with great extent compared to non-inoculated and control plants, thus reflecting the low effect of BmI4 on Cl compared to Sp. These data sugget that to improve production of a potato cultivar it is necessary to select the best host in combination with beneficial bacterial inoculum (Pathak et al. \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Similarly, Molina-Romero et al. (2020) on maize showed differential responses between varieties, assigned to the bacteria colonization capacity. The BmI4 inoculum size should be optimized on Cl plants. Moreover, for Cl plants, other culture seasons should be considered to obtain tubers.\u003c/p\u003e \u003cp\u003eProline is a biochemical marker of salt stress response in plants (Egamberdieva et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). It is probably one of the most studied amino acids acting against abiotic stress response such as salt by balancing the adverse osmotic potential that prevents water uptake. We noticed a significant increase of proline content in inoculated Sp plant when submitted to 25 days of salt stress. Besides its osmoprotectant role, proline can act as a potent non enzymatic antioxidant (Rejeb et al. \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2014\u003c/span\u003e ; Jim\u0026eacute;nez Arias et al. 2021).\u003c/p\u003e \u003cp\u003eThe inoculation with BmI4 strain improved Sp tuber nutritional quality in comparison to control, marking great advantageous quotation. Salinity is suggested to decrease tuber dry matter by retardation of carbohydrate translocation from the leaves (Dahal et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). In the fresh market, consumers give great importance to the tuber appearance, whereas the industry processors require traits that confer frying quality such as dry matter, low reducing sugars and absence of physiological disorders. Higher dry matter provides advantages of higher processing yield, less fat absorption, better texture without affecting the taste. On the other hand, low sugar contents prevent the darkening of the processed potato products, which compromises the appearance and flavor of the fried product (Silva et al. \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Kammoun et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Tubers obtained in this study from BmI4-treated plants showed the lowest reducing sugars and higher dry matter (19.5%) compared to tubers of non-inoculated plants under salt stress conditions (12.59%). These data suggest that BmI4 inoculation improved tuber quality, which required for processing and culinary use. These tubers from inoculated plants showed the highest carotenoid contents under salt stress conditions, suggesting better antioxidant capacity of these potatoes compared to those of the non-inoculated plants. The increase of total proteins and nitrogen in tubers of plants treated with BmI4 might be related to the bacteria ability of nitrogen fixation (Ghazala et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Although the above documented evidences indicated that some benefit bacteria strains showed sutable potential to be used for potato growth and yield promotion under salt stress, to the best of our knowledge this is the first report showing this quality improvement.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study demonstrated that the BmI4 strain protected potato plants against salt stress. It substantially alleviated salt stress-mediated decrease of the growth and development, more significantly in Sp variety than in Cl. The inoculation resulted in an increase of auxin content and a reduction of oxidative stress (MDA and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) in Sp and Cl plants. These factors, together with the enhancement of chlorophyll, proline and antioxidant SOD, CAT, GPX activities, boosted the growth and ultimately resulted in a higher tuber production in Sp variety. Furthermore, the current investigation indicates that BmI4 inoculation promoted tuber quality, thereby adding a new dimension to the benificial effect. Therefore, the application of BmI4 strain may be a promising technique to promote potato crop in saline areas.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAcknowledgement\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors would like to thank the Tunisian Ministry of High Education and Scientific Research for supporting this work.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJSG effectuated all the expriments with OB. \u0026nbsp; She did the \u0026nbsp;statistical analysis \u0026nbsp;and \u0026nbsp; wrote \u0026nbsp;the first draft of the manuscript. IG and AH identified and characterized the bacterial strain in previous works. They contributed in the preparation of BmI4 inoculum. IG participated in the exprimental step. ONE conceived and designed the research approach and corrected the manuscript. RGB provided suggestions for the experimental design and revised the article prior to submission. All authors have read and approved the final copy of the manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no competing interests to declare.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors confirm that the data supporting the findings of this study are available within the article and supplementary material.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAbbas R, Rasul S, Aslam K, Baber M, Shahid M, Mubeen F, Naqqash T (2019) Halotolerant PGPR: a hope for cultivation of saline soils. J King Saud Univ Sci 31:1195\u0026ndash;1201. https://doi: 10.1016/j.jksus.2019.02.019\u003c/li\u003e\n \u003cli\u003eAcu\u0026ntilde;a JJ, Jorquera MA, Mart\u0026iacute;nez OA, Menezes-Blackburn D, Fern\u0026aacute;ndez MT, Marschner P, \u003cstrong\u003eGreiner R, Mora ML\u003c/strong\u003e (2011) Indole acetic acid and phytase activity produced by rhizosphere bacilli as afected by pH and metals. J Soil Sci Plant Nutr 11:1\u0026ndash;12\u003c/li\u003e\n \u003cli\u003eAebi H (1984) Catalase in vitro. Methods Enzymol 105:121\u0026ndash;126\u003c/li\u003e\n \u003cli\u003eAli B, Hafeez A, Ahmad S, Javed MA, Sumaira, Afridi MS, Dawoud TM, Almaary KS, Muresan CC, Marc RA, Alkhalifah DHM, Selim S (2022) \u003cem\u003eBacillus thuringiensis\u003c/em\u003e PM25 ameliorates oxidative damage of salinity stress in maize via regulating growth, leaf pigments, antioxidant defense system, and stress responsive gene expression. 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INRA Edit pp 552\u0026ndash;577\u003c/li\u003e\n \u003cli\u003eBates LS, Waldren RP, Teare ID (1973) Rapid determination of free proline for water-stress studies. Plant Soil 39(1):205\u0026ndash;207. https://doi.org/10.1007/BF00018060\u003c/li\u003e\n \u003cli\u003eBatool T, Ali S, Seleiman MF, Naveed NH, Ali A, Ahmed K, Abid M, Rizwan M, Shahid MR, Alotaibi M, Al-Ashkar I, Mubushar M (2020) Plant growth promoting rhizobacteria alleviates drought stress in potato in response to suppressive oxidative stress and antioxidant enzymes activities. Sci Rep 10(1):16975. https://doi: 10.1038/s41598-020-73489-z\u003c/li\u003e\n \u003cli\u003eBen Jeddou K, Maktouf S, Ghazala I, Frikha D, Ghribi D, Ellouz-Ghorbel R, Nouri-Ellouz O (2014) Potato peel as feedstock for bioethanol production: a comparison of acidic and enzymatic hydrolysis. 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Hortic Bras 37:095\u0026ndash;100. https://dx.doi.org/10.1590/S0102-053620190115\u003c/li\u003e\n \u003cli\u003eTahir M, Ahmad I, Shahid M, Shah GM, Farooq ABU, Akram M, Tabassum SA, Naeem MA, Khalid U, Ahmad S, Zakir A (2019) Regulation of antioxidant production, ion uptake and productivity in potato (\u003cem\u003eSolanum Tuberosum\u003c/em\u003e L.) plant inoculated with growth promoting salt tolerant \u003cem\u003eBacillus\u003c/em\u003e strains. Ecotox Enviro Saf 178:33\u0026ndash;42. https://doi: 10.1016/j.ecoenv.2019.04.027\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"potato-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"potr","sideBox":"Learn more about [Potato Research](http://link.springer.com/journal/11540)","snPcode":"11540","submissionUrl":"https://www.editorialmanager.com/potr/default2.aspx","title":"Potato Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Potato, Salinity, Plant growth-promoting bacteria, Auxin stimulation, Plant production, Tuber quality","lastPublishedDoi":"10.21203/rs.3.rs-3883973/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3883973/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSalinity is one of the major threats to potato. As the first vegetable crop, improving its production under salinity stress is with great interest. In a previous work, \u003cem\u003eBacillus mojavensis\u003c/em\u003e I4 (BmI4) plant growth-promoting (PGP) bacterial strain was isolated from the soil. Since BmI4 showed a growth capacity under salt conditions (10% NaCl) we decided here to evaluate its PGP capacity on potato plants (Spunta and Claustar varieties) grown in the greenhouse in the presence of 100 mM NaCl. Stem elongation and diameter, leaf number, area and organ fresh weights were monitored during 40 days of culture as well as tuber yield, caliber and composition. Our results showed that the inoculation of plantlet roots with BmI4 enhanced plant growth under salinity, particularly for Spunta variety. These beneficial effects were associated with an increase of auxin levels in plants from both varieties. The assessment of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and malondialdehyde contents revealed that BmI4 inoculation led to reduced oxidation in plants submitted to salinity, via the increase of superoxide dismutase, catalase and peroxidase activities. Moreover, the BmI4 treatment enhanced proline accumulation especially in leaves of Spunta variety. BmI4 inoculated plants from Spunta variety exhibited an early induction of tuberization associated with an increase of tuber yield and caliber under both culture conditions. These findings suggest that inoculation of potato with BmI4 can be promising strategy to improve plant culture in saline areas. Moreover, inoculation improved tuber composition.\u003c/p\u003e","manuscriptTitle":"Effect of the plant growth-promoting bacteria strain Bacillus mojavensis I4 on potato growth, physiology, tuber yield and quality under salt stress conditions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-29 06:50:52","doi":"10.21203/rs.3.rs-3883973/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-06-08T07:35:01+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-01-24T07:34:40+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-01-24T06:54:18+00:00","index":"","fulltext":""},{"type":"submitted","content":"Potato Research","date":"2024-01-20T05:59:09+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"potato-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"potr","sideBox":"Learn more about [Potato Research](http://link.springer.com/journal/11540)","snPcode":"11540","submissionUrl":"https://www.editorialmanager.com/potr/default2.aspx","title":"Potato Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"6b451ad5-88a1-4698-98d6-23e42f6cff80","owner":[],"postedDate":"January 29th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-12-02T16:00:23+00:00","versionOfRecord":{"articleIdentity":"rs-3883973","link":"https://doi.org/10.1007/s11540-024-09829-7","journal":{"identity":"potato-research","isVorOnly":false,"title":"Potato Research"},"publishedOn":"2024-11-25 15:57:10","publishedOnDateReadable":"November 25th, 2024"},"versionCreatedAt":"2024-01-29 06:50:52","video":"","vorDoi":"10.1007/s11540-024-09829-7","vorDoiUrl":"https://doi.org/10.1007/s11540-024-09829-7","workflowStages":[]},"version":"v1","identity":"rs-3883973","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3883973","identity":"rs-3883973","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}