Exploring endophytic bacteria for biocontrol and growth promotion in rice against brown spot and sheath blight...

Rice is one of the world's most critical crops, serving as a staple food for more than half of the global population and playing a vital role in global food security. However, rice production is frequently threatened by diseases such as brown spot and sheath blight, which can significantly reduce yields and impact food availability. Currently, these diseases are often managed using synthetic fertilizers and fungicides, which, while effective, pose serious environmental risks due to their indiscriminate use. The reliance on these chemicals not only harms ecosystems but also contributes to soil degradation and water pollution, exacerbating environmental challenges. In response, there is a growing need for sustainable and eco-friendly alternatives. Endophytic bacteria, which reside within plant tissues, offer a promising solution as they can provide effective disease control while promoting plant growth without the environmental drawbacks associated with synthetic chemicals4. Given their potential, this study aimed to evaluate bacterial endophytes from the rice cultivar SR4 for their ability to manage brown spot and sheath blight diseases, exploring their role as biocontrol and growth-promoting agents in rice. A total of 100 bacterial endophytes were isolated and evaluated for inhibition against Bipolaris oryzae and Rhizoctonia solani using dual culture assay. A few endophytes significantly inhibited the colony growth for both pathogens significantly (p ≤ 0.05). The highest inhibition was shown by Ureibacillus massiliensis (75.47 %) and Brucella rhizosphaerae (75.25 %) in Bipolaris oryzae and Rhizoctonia solani, respectively. Identification of the antagonistic endophytes was performed through morphological and molecular assay including 16S rRNA gene sequencing. The endophytes were further evaluated for their production of volatile compounds, chitinase, siderophores, and hydrogen cyanide (HCN), as well as their ability to promote rice growth through phosphorus solubilization, nitrogen fixation, ammonia production, and auxin and gibberellic acid production. Under greenhouse conditions, the highest disease control (≥70 %) was demonstrated by Brucella rhizosphaerae, Stenotrophomonas rhizophila, Ureibacillus massiliensis. Notably, these three species, which were identified as novel biocontrol agents in rice, showed promising results in both growth promotion and disease suppression. Their novelty lies in their previously unreported efficacy as biocontrol agents against brown spot and sheath blight in rice, highlighting their potential for future applications. With continued research and development, these endophytes could play a significant role in reducing the reliance on synthetic chemicals in rice cultivation, contributing to more sustainable and environmentally friendly agricultural practices.