P-224 - Uncovering Mutualistic Root-Inhabiting Bacteria that Promote Sustainable Rice Growth in Low-Input Paddy Fields

Plants rely on mutualistic associations with root-inhabiting microbes to adapt to diverse environmental conditions. However, the mechanisms underlying the establishment of these beneficial interactions remain poorly understood. In this study, we screened for plant growth-promoting (PGP) bacteria residing in the roots of paddy rice, where mycorrhizal symbiosis is typically limited. Our screening was conducted using rice roots grown in a unique paddy field that has been managed without chemical fertilizers or pesticides for over 70 years, yet consistently achieves 60–70% of the yield observed in conventionally fertilized fields in the same region. From this field, we isolated a collection of bacterial strains that, when inoculated onto rice seeds and seedlings, significantly enhanced plant biomass under both nutrient-deficient and nutrient-sufficient conditions. These findings underscore the vital role of mutualistic bacteria in facilitating rice adaptation to low-input paddy fields and highlight their potential application in sustainable rice cultivation. Further genetic and cellular analyses of inoculated plants revealed specific host genetic requirements and different colonization strategies employed by these beneficial bacteria.