Increased resistance to late leaf spot disease in transgenic peanut using a combination of PR genes

Peanut (Arachis hypogaea L.) is the sixth most important oil seed crop in the world. Yield loss due to Cercospora leaf spot (early and late leaf spots) is a serious problem in cultivating this crop. Non-availability of resistant genes within crossable germplasms of peanut necessitates the use of a genetic engineering strategy to develop genetic resistance against various biotic stresses. The pathogenesis-related (PR) proteins are a group of plant proteins that are toxic to invading fungal pathogens, but are present in trace amounts in plants. The PR proteins, PR-5 and defensins, are potent antifungal proteins. A double gene construct with SniOLP (Solanum nigrum osmotin-like protein) and Rs-AFP2 (Raphanus sativus antifungal protein-2) genes under separate constitutive 35S promoters was used to transform peanut plants. Transgenic peanut plants expressing the SniOLP and Rs-AFP2 genes showed enhanced disease resistance to late leaf spot based on a reduction in number and size of lesions on leaves and delay in the onset of Phaeoisariopsis personata leaf spot disease. PCR, RT-PCR, and Southern hybridization analyses confirmed stable integration and expression of these genes in peanut transgenics. The results demonstrate the potential of SniOLP and Rs-AFP2 genes in developing late leaf spot disease resistance in transgenic peanut.