Biological control of Rhizoctonia solani Kuhn on rice using mycoparasites

Abstract

The present investigation was undertaken to assess the effects of mycoparasite-fungicide combinations on the intensity of sheath blight disease, and also the effect of the same on the rhizosphere and phylloplane mycoflora of rice. An attempt has also been made to identify efficient mycoparasites of Rhzoctonia solani naturally present on the rhizosphere and phylloplane of rice plants. Several fungi isolated from the rhizosphere and phylloplane of rice plants were found to exhibit strong antagonistic action against R. solani, in vitro. Antagonistic fungi such as Trichoderma viride, T. harzianum, Aspergillus niger caused granulation, vacuolation and finally disintegration of R. solani hyphae. The ability of the antagonists to produce volatile as well as diffusible metabolites was also assessed. T. viride was found to be very efficient in inhibiting the growth of R. solani, as a result of the diffusible as well as volatile metabolites produced by the fungus. T. harzianum was also very efficient in inhibiting growth of R. solani. When the antagonist T. viride was mass cultured in various growth substrates and tried for their efficacy as potential biocontrol agents of sheath blight disease of rice, rice bran as well as wheat bran turned out to be the best growth substrates. Under pot culture conditions, where the efficacy of various mycoparasite- fungicide combinations in checking sheath blight was assessed, T. viride was the best mycoparasite and edifenphos the best fungicide. The rhizosphere mycoflora was enhanced by application of mycoparasite, especially T. viride and T. harzianum. Among fungicides application of edifenphos resulted in increased rhizosphere mycofloral population. In the case of phyllooplane mycoflora application of mycoparasites have a suppressive effect. Treatments of edifenphos increased phylloplane mycofloral population. Under field conditions also T. viride emerged as the best mycoparasite and ediphenphos as a superior fungicide in checking sheath blight. T. viride + ediphenphos was also found to be very efficient in controlling sheath blight disease. The highest grain and straw yields were obtained in treatment with the mycoparasite T. viride, and fungicide edifenphos. The treatment combination T. viride + edifenphos also gave the highest yield. In the case of rhizosphere mycoflora application of mycoparasites enhanced the population. Mycoparasites were found to have a suppressive effect on the fungal population on the leaf surface.