Harnessing soil yeast for moisture stress mitigation and growth promotion during rice germination

Moisture stress is one of the major factors affecting crop productivity and food security. Although several management practices are available, eco-friendly microbial approaches provide sustainable solutions through mechanisms such as nutrient solubilization, phytohormone production, biofilm formation, osmolyte accumulation and metabolite production. Among plant growth-promoting microbes, yeasts remain less explored for their role in drought tolerance. The present study aimed to evaluate the potential of yeast in mitigating moisture stress and promoting rice growth. Fifty isolates were obtained from soil samples, of which 18 isolates survived up to 30% PEG 6000. Further, the isolates were evaluated for plant growth-promoting (PGP) traits, including the indole acetic acid, siderophore, and exopolysaccharides production, phosphorus and zinc solubilization, and biofilm formation under increasing PEG concentrations (0, 10, 20 and 30%). Among the 18, five well-performing isolates S2R2, CAL, SF, SA1, and V1BG were selected for further experiments. All these five isolates demonstrated ACC deaminase activity (maximum of 111.50 nmole of α-ketobutyrate mg^- 1 protein h^- 1) and osmolytes accumulation such as proline, trehalose and glycine betaine. Moreover, these isolates on seed biotization improved seed germination and seedling growth under moisture stress. Metabolite profiling revealed that production of phenols, alkaloids, and amino acids was predominant under PEG-induced stress and associated with plant growth promotion. Overall findings highlight the potential of yeast as bioinoculants for enhancing drought resilience and growth promotion in rice.