ENHANCEMENT OF SALT TOLERANCE IN RICE THROUGH PLANT GROWTH-PROMOTING RHIZOBACTERIA

Abstract

The ongoing expansion of global salt-affected land is a significant factor limiting crop growth and yield, particularly for rice. This experiment explores the mitigation of saltinduced damage on rice (Oryza sativa L. cv BRRI dhan100) by applying plant growthpromoting

rhizobacteria (PGPR) cultures. This experiment followed a completely randomized design (CRD) and experimental duration was December 2022 to May 2023. where rice seedlings, five and six weeks post-transplanting, were subjected to salt stress via two treatments with 50 and 100 mM NaCl at seven-day intervals. Bacterial cultures, comprising endophytic PGPR strains (Bacillus subtilis and B. aryabhattai) and an epiphytic PGPR strain (B. aryabhattai), were administered at three critical stages: during transplantation of 42-d-old seedlings, five weeks later at the vegetative stage at 35 days after transplanting (DAT), and seven weeks later at 49 DAT during panicle initiation stage. Salt stress prompted osmotic, ionic, and oxidative stress in rice plants, causing a dose-dependent decrease in relative water content, chlorophyll content, stomatal conductance, chlorophyll fluorescence, IAA concentrations, and various growth parameters. Furthermore, osmotic stress escalated the hydrogen peroxide content and proline accumulation, while ionic stress disrupted ion balance by increasing Na + and reducing K + content. Both types of stress generated reactive oxygen species, impairing the antioxidant defense system and causing oxidative damage, visible in heightened malondialdehyde levels and electrolyte leakage. PGPR treatment alleviated these negative effects by enhancing osmotic and ionic balance, demonstrated by improved water balance and reduced Na + content and Na + /K + ratio. Additionally, PGPR fortified the antioxidative defense system in salt-exposed rice plants by increasing ascorbate and glutathione levels. The introduction of PGPR led to enhancements in yield attributes (including effective tillers per hill, panicle length, rachis per panicle, filled grains per panicle, and 1000-grain weight), consequently boosting the grain yield per hill. In conclusion, this research highlights the potential of PGPR to bolster physiological and biochemical functionality in rice, serving as an effective buffer against salt stress-induced damage