GENETIC TRANSFORMATION OF GROUNDNUT FOR RESISTANCE TO TIKKA DISEASE

Abstract

Groundnut is grown worldwide as an important cash crop and its seeds are a major source of premium quality vegetable oil and protein. Yield loss up to 70 per cent has been reported due to reduced photosynthesis resulting from increase in necrotic leaf area and defoliation after severe attack of leaf spot disease. The best way to control this foliar disease is to grow resistant cultivars, but higher levels of resistance are not available in groundnut cultivars. Genetic transformation is the best alternative in such circumstances and availability of efficient regeneration and gene delivery systems is a prerequisite for this technique. Therefore during present study, regeneration protocols were standardized by culturing three explants of each of four commercial varieties on MS medium supplemented with different hormone combinations, subsequently followed by transformation of best responding variety with chitinase gene. 78.33 per cent cotyledonary explants responded to shoot induction with 5.14 shoots/explant in Golden variety on MS medium containing 0.1 mg/l NAA and 4 mg/l BAP. Roots were induced successfully (61.30 per cent) on MS medium fortified with 1.0 mg/l NAA. Direct shoots were induced from 52.67 per cent leaf disc explants. Somatic embryos were obtained (98.33 per cent) from epicotyl explants on MS medium having 8mg/l picloram. 14.18per cent transformation efficiency through Agrobacterium, 6.88per cent by silicon carbide whisker and 6.59per cent by gene gun method has been achieved. This is first known report of Silicon carbide whisker mediated transformation in peanut in world. The transgene (RCG3) over expressed well and showed significant resistance to the Tikka disease. 12 In present study it has been proven that rice chitinase gene (RCG-3) confers strong resistance against leaf spot disease of peanut. The stable peanut lines produced will be helpful to evolve cultivars with built-in solution to control fungal diseases, specially the leaf spot. The standardized protocols of regeneration and transformation will be used for incorporation of other desirable genes in this crop.