Screening of Biocontrol Agents Against Rhizoctonia solani Causing Web Blight Disease of Groundnut (Arachis hypogaea L.)

Abstract

Soil borne plant pathogenic fungi cause heavy crop losses all over the world. With variable climate from region to region, most of the crops grown in India are susceptible to diseases caused by soil borne fungal pathogens. Among tropical, subtropical land crops groundnut (Arachis hypogaea L.) is an important annual oil seed crop, which provides vegetable oil as human food and oil cake meal as animal poultry feed. A large number of diseases attack groundnut in India (Ganesan and Sekar, 2004a). Fungi cause majorities and several of them are yield reducers in certain region and seasons (Bowyer, 1999). Among the soil borne fungal diseases of groundnut, Web blight, caused by Rhizoctonia solani is the most common disease (Dubey, 2000). Majority of work done on plant disease biocontrol relate to soil borne diseases using either bacteria or fungal antagonists (Montealegre et al., 2003; Askar and Rashad, 2010; Pandya and Saraf, 2010). Among bacteria, Pseudomonas and Bacillus spp. are widely used. However, the use of antagonistic fungi, especially Trichoderma and Gliocladium spp. has been more extensive than their bacterial counterparts (Harman, 2000; Ganesan, 2004; Harman, 2006; Neha and Dawande, 2010). Bacteria isolated from the rhizosphere and belonging to a wide variety of genera have the potential to suppress diseases caused by a diversity of soil borne plant pathogens. But the information available on the antagonistic effect of rhizobacteria against R. solani is very scanty. Rhizoctonia solani Kuhn (teleomorph: Thanatephorus cucumeris (A.B. Frank) Donk is a widespread and an ecologically diverse soil-borne fungus, causing different types of diseases in many plant species. It causes root rot, stem rot, fruit and seed decay, damping-off, foliar blight, stem canker and crown rot in various crops (Guleria et al., 2007). Understanding the mechanism of action is important because it gives much useful information in determining the maintenance, enhancement and implementation of biological control. Biological control agents interact with phytopathogens directly or indirectly to reduce the population of pathogens or reduction in the ability of the pathogens to cause disease. In general, mechanisms implicated in antagonism towards the biological control of phytopathogenic fungi includes, A) Direct mechanism: parasitism, antibiosis, competition for nutrients or space, production of enzymes and inactivation of pathogen enzymes. B) Indirect mechanism: tolerance to stress through enhanced root and plant