Stress-Tolerant Endophytic Isolate Priestia aryabhattai BPR-9 Modulates Physio-Biochemical Mechanisms in Wheat (Triticum aestivum L.) for Enhanced Salt Tolerance

In efforts to improve plant productivity and enhance defense mechanisms against biotic and abiotic stresses, endophytic bacteria have been used as an alternative to chemical fertilizers and pesticides. In the current study, 25 endophytic microbes recovered from plant organs of Triticum aestivum L. (wheat) were assessed for biotic (phyto-fungal pathogens) and abiotic (salinity, drought, and heavy metal) stress tolerance. Among the recovered isolates, BPR-9 tolerated maximum salinity (18% NaCl), drought (15% PEG-6000), and heavy metals (mu g mL(-1)): Cd (1200), Cr (1000), Cu (1000), Pb (800), and Hg (30). Based on phenotypic and biochemical characteristics, as well as 16S rDNA gene sequencing, endophytic isolate BPR-9 was recognized as Priestia aryabhattai (accession no. OM743254.1). This isolate was revealed as a powerful multi-stress-tolerant crop growth promoter after extensive in-vitro testing for plant growth-promoting attributes, nutrient (phosphate, P; potassium, K; and zinc, Zn) solubilization efficiency, extracellular enzyme (protease, cellulase, amylase, lipase, and pectinase) synthesis, and potential for antagonistic activity against important fungal pathogens viz. Alternaria solani, Rhizoctonia solani, Fusarium oxysporum, and Ustilaginoidea virens. At elevated salt levels, increases were noted in indole-3-acetic acid; siderophores; P, K, and Zn-solubilization; ACC deaminase; and ammonia synthesized by Priestia aryabhattai. Additionally, under in-vitro plant bioassays, wheat seedlings inoculated with P. aryabhattai experienced superior growth compared to non-inoculated seedlings in high salinity (0-15% NaCl) environment. Under NaCl stress, germination rate, plant length, vigor indices, and leaf pigments of wheat seedlings significantly increased following P. aryabhattai inoculation. Furthermore, at 2%-NaCl, B. aryabhattai greatly and significantly (p <= 0.05) decreased relative leaf water content, membrane damage, and electrolyte leakage compared with the non-inoculated control. Catalase, superoxide dismutase, and peroxidase activity increased by 29, 32, and 21%, respectively, in wheat seedlings exposed to 2% NaCl and inoculated with the bacteria. The present findings demonstrate that endophytic P. aryabhattai strains might be used in the future as a multi-stress reducer and crop growth promoter in agronomically important crops including cereals.

Automated summary

Endophytic bacteria can be used as an alternative to chemical fertilizers and pesticides to improve plant productivity and enhance defense mechanisms against various stresses. In this study, the endophytic isolate BPR-9, identified as Priestia aryabhattai, showed high tolerance to salt, drought, and heavy metal stresses, and exhibited positive effects on crop growth promotion and inhibition of fungal pathogens. Wheat seedlings inoculated with P. aryabhattai showed superior growth under high salt conditions. These findings suggest that endophytic P. aryabhattai strains have the potential to be used as multi-stress reducers and crop growth promoters in important agronomic crops.