Efficacy of Bacillus subtilis MBI 600 Against Sheath Blight Caused by Rhizoctonia solani and on Growth and Yield of Rice

Rice sheath blight disease (ShB), caused by Rhizoctonia solani, gives rise to significant grain yield losses. The present study evaluated the efficacy of Integral®, the commercial liquid formulation of Bacillus subtilis strain MBI 600, against rice ShB and for plant growth promotion. In greenhouse studies, four log concentrations of Integral (from 2.2×10⁶ to 2.2×10⁹ cfu/mL) were used as seed treatment (ST). After 25 d, seedlings were dipped (SD) into Integral prior to transplanting. At 30 d after transplanting (DAT), leaf sheaths were inoculated with immature sclerotia of the pathogen. At 45 DAT, a foliar spray (FS) with Integral was applied to some treatments. The fungicide control was 50% carbendazim at 1.0 g/L, and a nontreated control was also included. Overall, there were 10 treatments, each with five replications. ShB severity was rated at 52 DAT, and seedling height and number of tillers per plant were rated at 60 DAT. In 2009, two field trials evaluated Integral at 2.2×10⁸ and 2.2×10⁹ cfu/mL. Integral was applied as ST, and seedlings were produced in a nursery bed. After 32 d, seedlings were treated with Integral as SD and transplanted into 10 m² blocks. Foliar sprays were given at 45 and 60 DAT. There were seven treatments, each with eight replications arranged as a factorial randomized complete block design. At 20 DAT, the plots were broadcast inoculated with R. solani produced on rice grains. Seedling height before transplanting, ShB severity at 90 DAT, and grain yield at harvest were recorded. Integral at 2.2×10⁹ cfu/mL provided significant increase of seedling heights over other treatments under greenhouse conditions. The Integral treatments of ST + SD + FS at 2.2×10⁹ cfu/mL significantly suppressed ShB over other treatments. In field studies, Integral provided significant increase of seedling height in nursery, and number of tillers per plant, compared with the control. ShB severity was significantly suppressed with higher concentrations of Integral compared to lower concentrations. Grain yield were the highest at an Integral concentration of 2.2×10⁹ cfu/mL. Overall, Integral significantly reduced ShB severity, enhanced seedling growth, number of tillers per plant and grain yield as ST + SD + FS at the concentration of 2.2×10⁹ cfu/mL under the conditions evaluated.