Biological control efficacy of Bacillus sp. REB711 on sheath blight of rice

Sheath blight (ShB), caused by Rhizoctonia solani, is one of the economically important rice diseases in Louisiana and other rice-growing regions. Fungicides are used to manage ShB but such chemical methods are not economically or ecologically sustainable. To develop new biological control agents for the management of ShB, bacteria isolated from rice plants in the field were initially screened in the laboratory based on their antagonistic activities against R. solani through plate assays that exhibit growth inhibition of the fungal pathogen. Efficacy of three selected strains of Bacillus spp. (RAB14R, REB711, and RRB985) in suppression of ShB was further evaluated under the greenhouse and field conditions. In field trials conducted in 2017 and 2018, foliar spray of Bacillus sp. REB711 significantly reduced the development of ShB compared to the non-treated control, although it was less effective than the azoxystrobin fungicide Quadris®. In greenhouse tests, Bacillus sp. REB711 significantly reduced ShB development (disease severity and lesion length) through seed treatment, while the other two strains of Bacillus spp. did not. The observed efficacy of Bacillus sp. REB711 could result from competition, antibiosis, and/or induction of plant defense system, and suggests that this bacterial strain could be used a potential biological agent for managing ShB by itself or in combination with fungicides to reduce the risk of fungicide resistance.