Biochemical and molecular studies of early blight disease in tomato

Tomato early blight occurs worldwide and it is prevalent wherever tomatoes are grown. Alternaria solani Sorauer, the causal agent, has been recognized as a serious foliar pathogen of tomato and there are very few cultivars which possess resistance against early blight. Alternaric acid is the major toxin of A. solani. In this study, alternaric acid and fungal culture filtrate were used as an elicitor in NDT-96 (tolerant) and GP-5 (susceptible) tomato varieties in order to study and compare their abilities to induce defense-related enzymes, viz., catalase, peroxidase, β-1,3 glucanase, phenylalanine-ammonia-lyase (PAL), chitinase and polyphenol-oxidase (PPO) along with total phenols, and total soluble proteins. NDT-96 showed a rapid induction of all these pathogenesis-related enzymes except catalase along with total phenols as compared to GP-5 with both the treatments. Differential expression of total soluble proteins revealed higher protein content in NDT-96 as compared with GP-5. A 49.48 kDa protein was observed to be absent in GP-5. In addition, 25 microsatellite markers (SSR) were screened for polymorphisms among the above mentioned two tomato varieties. Of these, SSR 286 revealed a significant polymorphic band of 108 bp in NDT-96.