Evaluation and selection of elite plant growth-promoting rhizobacteria for suppression of sheath blight of rice caused by rhizoctonia solani in a detached leaf bio-assay.

Sheath blight (ShB) of rice, caused by Rhizoctonia solani, is one of the most important rice diseases worldwide. The objective of this study was to screen selected plant growth-promoting rhizobacteria (PGPR) strains for suppression of ShB under controlled conditions. Sclerotia of R. solani were produced on PDA and immature sclerotia (< 5-day-old) were harvested. Leaves of 60-day-old rice plants grown under greenhouse conditions were used to screen PGPR strains by detached leaf assay. Leaf sections of 8 cm in length were cut and placed in Petri dishes, inoculated with immature sclerotia, and incubated in a growth chamber. Approximately 70 PGPR strains were screened. The disease was quantified by the Relative Lesion Height (RLH) method. Among 70 strains, 31 significantly suppressed the RLH of ShB lesions compared to the control. Among these, Bacillus subtilis strain MBI 600 resulted in greatest suppression of ShB disease severity under the conditions tested.