Isolation and identification of an antagonistic bacterium against Rhizoctonia solani, the causing agent of rice sheath blight

Abstract:

[Objective] This study is aimed to isolate and characterize antagonistic bacteria from soil, and evaluate their in vitro inhibition and control efficacy against Rhizoctonia solani, the causing agent of rice sheath blight in a green house. [Methods] Serial dilution method and dual culture technique on agar plate were used for screening bacteria. Strain identification was based on morphological and physiological characteristics, and phylogenetic analysis of 16S rDNA sequence. Control efficacy against rice sheath blight was evaluated by seed bacterization tests in a green house. [Results] An antagonistic bacterial strain against Rhizoctonia solani was isolated and screened from vegetable rhizosphere soil. The strain, designated as kwkjT4, exhibited excellent in vitro inhibition against the fungal pathogen. Its control efficacy against rice sheath blight was comparable to that of jinggangmycin. It was preliminarily identified as a strain of Chromobacterium pseudoviolaceum. The optimal growth conditions of the strain were as follows: pH 7.0, temperature 32 °C, incubation time 36 h. Inconsistence with those for the bacterial growth, the optimal conditions for accumulating inhibitory substances were pH 6.0, temperature 28 °C, and incubation time 48 h. [Conclusions] Strain kwkjT4 had potentials for the biological control of rice sheath blight. This is the first report on the antagonism of C. pseudoviolaceum against Rhizoctonia solani.