Abstract

BIOCONTROL OF RHIZOCTONIA SOLANI BY STREPTOMYCES CACAOI SUBSP CACAOI.M20

Dr. T. Janaki*

ABSTRACT

Plant diseases of economic crops alone cause 13-20% annual loss in production. About 90% of the 2000 major diseases of the 31 principal crops in US are caused by soil borne plant pathogens. The use of chemical fungicides causes major problems like bio-concentration and bio-magnification in living system through food chain and food web. In order to avoid these problems, use of bio-fungicides are being introduced and practiced. A total of 25 actinomycetes were isolated from the soil sample of Avicennia marina from Ariyankuppam back water area, Puducherry. These were screened for fungicidal activity, among these, the isolate M20 found to be better in antifungal activity. The isolate M20 was characterized further for identification. The active isolate M20 was identified as Streptomyces cacaoi subsp cacaoi with 98.6% similarity with already reported sp (NRBC 12748(T)-AB184115. The isolate M20 produced chitinolytic enzymes. The phytotoxicity study was done with 10%, 25%, 50%, 75% and 100% culture filtrate (CF). As the 10% CF was better in seed germination and also actively controlled the growth of Rhizoctonia solani (94.4%), 10% CF was taken as standard concentration for biocontrol of Rhizoctonia solani using Paddy as the test plants. The 15th day Paddy plants under treatment with A and A+P yielded high biomass and better growth. The disease development by the pathogen also controlled by the antagonist (A) (isolate M20). Since the isolate M20 controlled the growth and disease causing potentiality of Rhizoctonia solani, it can be effectively used to control seed and soil borne diseases as bio-fungicide.

Keywords: Avicennia marina, Phytotoxicity, Rhizoctonia solani, Biocontrol, Bio-fungicide, Mangrove actinomycetes.