Drought-tolerant rhizobacteria with predicted functional traits enhanced wheat growth and P uptake under moderate drought and low P-availability

This study aims to investigate the effect of isolated drought-tolerant rhizobacteria, spanning various groups, such as nitrogen-fixing bacteria (NFB), phosphate solubilizing bacteria (PSB), and other plant growth promoting rhizobacteria (PGPR), on the growth of wheat (Triticum durum) plants, focusing on various morphological and physiological responses under moderate drought and low-P availability. Among 343 rhizobacterial morphotypes, 16 exhibited tolerance to NaCl and PEG-6000. These included 8 PSB, 4 NFB, and 4 osmotolerant-PGPR groups, distributed across 14 different genera. Biochemical characterization showcased diverse PGP capabilities, particularly in P solubilization. The dynamic responses of drought-tolerant PSB to salt and PEG-6000-induced drought stress involved variations in organic acid (OA) secretion, with specific acids, including palmitic, lactic, and stearic, playing crucial roles in enhancing available P fractions. Inoculation with rhizobacteria significantly increased both shoot (SDW) and root (RDW) dry weights of wheat plants, as well as rhizosphere available P. PSB₁₁ (Arthrobacter oryzae) emerged as the most effective strain, plausibly due to its positive impact on root morphological traits (length, surface, and volume). Other isolates, PSB₁₀ (Priestia flexa), PSB₁₃ (Bacillus haynesii), and particularly PGPR₂ (Arthrobacter pascens) significantly increased shoot P content (up to 68.91 %), with a 2-fold increase in chlorophyll content. The correlation analysis highlighted positive associations between SDW, shoot P content, chlorophyll content index (CCI), and leaf area. Additionally, a negative correlation emerged between microbial biomass P and root morphophysiological parameters. This pattern could be explained by reduced competition between plants and rhizobacteria for accessible P, as indicated by low microbial biomass P and strong plant growth. Our investigation reveals the potential of drought-tolerant rhizobacteria in enhancing wheat resilience to moderate drought and low-P conditions. This is demonstrated through exceptional performance in influencing root architecture, P utilization efficiency, and overall plant physiological parameters. Beyond these outcomes, the innovative isolation procedure employed, targeting rhizobacteria from diverse groups, opens new avenues for targeted isolation techniques. This unique approach contributes to the novelty of our study, offering promising prospects for targeted bioinoculants in mitigating the challenges of drought and P deficiency in wheat cultivation.