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Stem rot caused by Sclerotium rolfsii Sacc. is a major constraint in the production and productivity of the groundnut. Management of stem rot disease is very difficult due to soil borne nature, wide host range of S. rolfsii and lack of disease resistance in existing commercial cultivars. Biological control with potential Streptomyces is receiving greater attention all over the world. Studies were conducted on collection and isolation of Streptomyces, their mechanism of action, cultural and morphological characteristics, its efficacy against S. rolfsii with Scanning electron microscope(SEM). Roving survey was conducted in major groundnut growing regions of Andhra Pradesh. During survey 180 soil samples were collected from groundnut rhizosphere and 50 Streptomyces isolates were isolated from different soil samples. Twenty Streptomyces isolates were tested for their growth rate and antifungal activity against groundnut stem rot pathogen, S.rolfsii under in vitro conditions using dual culture method. Among twenty isolates of Streptomyces, five isolates showed maximum inhibition of S. rolfsii. These five isolates were characterized based on cultural and morphological characters. The study involved in differentiating various characters viz., type of spore chain, colony margins, shape of spore chains, colour of spore mass and spore surface. The morphology of the spore chains varied across the isolates showing the filamentous (Ggd), spiral (Kyd and Lrp) and Rectus flexibilis (Kdr and Mkc). SEM studies revealed that inhibition of the growth of S. rolfsii by Streptomyces was mainly due to exhibition of irregular distortions at contact site of the pathogen and collapse of the fungal hyphae and this might be due to the production of secondary metabolites and extracellular enzymes.
J. et al. (Sat,) studied this question.