Screening bacterial isolates for biocontrol of sheath blight in rice plants

Sheath blight (Rhizoctonia solani) causes significant yield losses in rice (Oryza sativa L.). Its sustainable management needs an efficient biocontrol agent. The objective was to screen bacterial isolates as an antagonist to R. solani and identify the most efficient ones as sheath blight suppressors under greenhouse conditions. Two assays (E1 and E2) were performed in a completely randomized design with three replications. E1 tested 21 bacterial isolates antagonists to R. solani in vitro. E2 was conducted under greenhouse conditions, with rice cultivar BRS Pampeira sown in plastic pots (7 kg) containing fertilized soil. Sixty old plants were inoculated with a segment of a toothpick containing fragments of R. solani, followed by spray inoculation of a bacterial suspension (10⁸ CFU/mL). The severity of the disease was determined by calculating the relative lesion size formed on the colm. Isolates BRM32112 (Pseudomonas nitroreducens), BRM65929 (Priestia megaterium), and BRM65919 (Bacillus cereus) reduced R. solani colony radial growth by 92.8, 77.56, and 75.56%, respectively while BRM63523 (Serratia marcescens), BRM65923 and BRM65916 (P. megaterium) and BRM65919 (B. cereus) with 23.45, 23.37, 23.62, and 20.17 cm, respectively were effective at suppressing sheath blight in greenhouse, indicating their potential as a biofungicide for sheath blight suppression.