Bacterial Communities and Soil Interactions in Sifra and Mondial Potatoes: Pathways to Sustainable Potato Production

Abstract Plant growth promoting rhizobacteria (PGPRs) play significant roles in improving plant growth. Likewise, Mycorrhizal Helper Bacteria (MHB) enhance AM fungi fitness by promoting spore germination and providing protection against pathogens. This PGPR and MHB synergistic association can be exploited to introduce inocula that utilize bacteria for sustainable potato production within potato agricultural systems. In this study, we isolated and identified PGPRs that dominate Sifra and Mondial potato soils across 3 developmental stages (sprouting, tuber bulking and at harvest). In addition, soil physicochemical properties were assessed, revealing soil pH as a key factor shaping bacterial community composition. Community structure in both soil samples was dominated by the phyla Actinobacteria, Proteobacteria, and Acidobacteria. The genera Sphingomonas and the families Conexibacteraceae and Cthoniobacteraceae were consistently abundant across all growth stages in both potato varieties, suggesting that these taxa represent dominant bacterial groups that are adapted to the acidic soils associated with Sifra and Mondial cultivation. Functional characterization identified nitrogen supplying bacterial species in Sifra soils while Mondial soils were enriched in biopolymer degrading bacteria reflecting a varietal influence of bacterial communities. Bacterial community was not affected by growth stage. To identify MHB, isolated bacteria from spore surfaces and within spores were cultured, compared using 16S rRNA gene sequencing, and tested for chitinase, protease, cellulase and phosphatase activity. MHB from the Mondial field were dominated by Sphingobium whilst those from the Sifra field were dominated by Bacillus species suggesting varietal influence of MHB associating with prevailing AM fungi species. All bacillus species facilitated phosphate solubilization, Indole Actic Acid (IAA) production and cellulase activity suggesting their roles in plant growth. Similarly, Mondial MHB had the same activity. Overall, the study highlighted varietal and environmental influence of plant PGPRs and MHB which can be exploited for sustainable potato production in South Africa. Highlights Soil physiochemical properties are affected by potato variety Interaction of plant variety and soil physicochemical properties influences plant microbiomes Mycorrhizal helper bacteria can possess plant growth promoting properties Plant growth stage does not necessarily influence rhizhospheric bacterial communities Competing Interest Statement The authors have declared no competing interest.