Survival of rhizoctonia solani kuhn with special reference to antagonistic soil microflora

Abstract

Studies were undertaken to make a critical assessment of the nature of survival and various factors affecting the survival of R. solani in soil. It was found that submerged condition reduced the competitive saprophytic ability of R. solani. Various agronomical and ecological factors influenced the survival of R. solani. Among the organic amendments paddy husk reduced the survival of R. solani and increased yield of rice. The survival of R. solani was maximum when the moisture level was 15 per cent, temperature between 200C and 300C, and at pH 7. Among the microorganisms isolated from the soils of Kerala, 14 species of fungi, and eight species of bacteria were antagonistic to R. solani. A. niger was inhibitory to 11 other fungi tested, while T. harzianum and T. viride were without much interaction with other antagonistic fungi. Alcaligenes sp. and Bacillus spp. were the bacteria antagonistic to other bacterial isolates and to all isolates of antagonistic fungi as well as to R. solani. The in vitro evalution of fungicides on R. solani and on antagonistic organisms reveled that ziram was less inhibitory to majority of antagonistic fungi, but was also least inhibitory to R. solani. Carbendazim, edifenphos and carboxin were very effective in suppressing the growth of R. solani, while they showed less inhibitory action on antagonistic fungi. Among the insecticides tested methyl parathion was found to be least inhibitory to many antagonistic fungi and also to R. solani. Herbicides, bentazone and thiobencarb were inhibitory to few antagonistic fungi and to R. solani. Results of the pot experiment showed that among the antagonists Trichoderma viride and T. harzianum and among the chemicals carboxin and bentazone were effective in reducing the survival of R. solani. Trichoderma harzianum, T. viride, Fusarium semitectum, F. solani and Aspergillus niger in combination with carboxin and carbofuran reduced the intensity of sheath blight. From the field experiments, it was observed that combination of carboxin + bentazone + carbofuran + T. viride was the best in reducing the disease as well as in increasing the grain and straw yield.