Exploring the Interaction Dynamics of Growth-Promoting Bacterial Endophytes and Fertilizer on Oryza sativa L. Under Heat Stress

The demand for rice (Oryza sativa L.) as a staple food continues to grow, but rising temperatures due to climate change pose a significant threat to its production. This study addresses the challenge by employing endophytic bacteria and fertilizer to mitigate the adverse effects of high temperatures on rice plants. Seedlings were evaluated for growth parameters, comparing outcomes with non-inoculated counterparts under normal and 40 to 45 °C heat shock conditions. Isolates underwent thorough DNA extraction and 16 S rRNA gene sequencing for identification and were scrutinized for their plant growth-promoting (PGP) traits. The effects of fertilizer and thermotolerant bacteria on rice plants were investigated in controlled chambers at 25 °C for 14 days, succeeded by exposure to 40 °C for 10 days. A consecutive soil pot experiment extended over 150 days, exposing plants to growth chambers set at 35 °C for 60 days, followed by a rapid increase to 40 °C for 30 days and a subsequent reduction to 35 °C for an additional 60 days. Inoculating with the isolates resulted in panicle development and increased plant biomass and length, with fresh grain weights showing a 50% improvement when using bacterial strain W (B. paralicheniformis). Additionally, dry grain weights per panicle rose by 113% with strain W, 83% with strain N (B. pumilus), and 87% with strain D (B. paranthracis) compared to the control. Bacterial strain W exhibited the most pronounced effect on rice yield under heat stress. The results demonstrated a decrease in malondialdehyde (MDA) levels after 150 days of heat stress and half-dose of the recommended fertilizer. Bacterial inoculation increased proline, salicylate, and abscisic acid content, suggesting the alleviation of osmotic stress effects. This highlights the role of endophytic bacteria in stimulating biologically active responses within rice plant cells. Notably, bacterial strains W, N, and D show potential for enhancing plant growth and mitigating heat stress when used in conjunction with NPK50.