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Department of Plant Pathology, ANGRAU-S.V. Agricultural College, Tirupati-517 502.
Groundnut (Arachis hypogaea L.) Stem rot disease of groundnut (Arachis hypogaea), caused by the fungus Sclerotium rolfsii Sacc., is one of the most destructive soilborne diseases affecting groundnut cultivation in the Rayalaseema region of Andhra Pradesh, India. A survey conducted across eight districts viz Tirupati, Kadapa, Chittoor, Annamayya, Kurnool, Nandyal, Ananthapur, and Sathya Sai revealed disease incidence ranging from 19.7 per cent to 31.2 per cent, with Kurnool recording the highest incidence (31.2%). In the present investigation, a total of 40 bacterial antagonists (GB1–GB40) and 14 actinobacterial isolates (GA1–GA14) were isolated from rhizospheric soil of healthy groundnut plants grown in these districts using serial dilution plating technique on Nutrient Agar (NA) medium and Starch Casein Agar (SCA) medium, respectively. All isolates were purified using the streak plate method. The pathogenicity of S. rolfsii was confirmed by proving Koch’s postulates, where in S. rolfsii inoculum grown on sorghum grains were used to artificially infest soil. After 10 days of inoculation, typical stem rot symptoms that includes yellowing, wilting and rotting of collar region along with occurrence of white cottony mycelial growth and brown sclerotia in inoculated plants, while uninoculated control plants remained healthy. The fungal pathogen was successfully re-isolated from infected plants, thereby satisfying Koch’s postulates. The collection of diverse antagonistic microorganisms from the rhizosphere of groundnut plants grown in Rayalaseema establishes a foundation for biocontrol-based integrated disease management strategies against groundnut stem rot.
KEYWORDS: Groundnut, stem rot, Sclerotium rolfsii, rhizosphere, bacterial antagonists, actinobacteria, biocontrol, rayalaseema, Andhra Pradesh.