Study of Biological Control of Rice Sheath Blight Caused by Rhizoctonia solani with Some Antagonistic Bacteria in the Guilan Province

Among 160 samples collected from rice paddy of the Guilan province including rice plant, seed, rhizospher, paddy's soil, paddy's water and sclerotium of the causal agent of rice sheath blight (Rhizoctonia solani), 610 bacterial strains were isolated. 71 bacterial strains (11.64%) had the ability of inhibition mycelial growth fungus in dual culture test on PDA medium. According to two characteristics of inhibition zone in dual culture and the inhibition percent from vegetative growth of causal agent of sheath blight in antifungal volatile metabolites production test, 37 antagonist strains were grouped in cluster analysis. The strains of antagonist which placed in the highest group on the based of antagonistic ability, identificated and selected for next experiments. Disease severity of sheath blight were evaluated under greenhouse conditions by the seed, soil and plant treatments at the presence of the antagonist strains. Results showed that there was significant difference between the plant treatment to other methods. The 152 (Pseudomonas aeruginosa) and 7S (Pseudomonas fluorescens bv3) strains with 26.59% and 33.59% on the reduction of disease severity respectivility showed the highest effect and placed in seperated group in comparison with control. Among three methods used, 152 (Pseudomonas aeruginosa) strain with 14.46% on the reduction of disease in comparison with control showed the lowest disease severity