Variations in total phenolics and antioxidant enzymes cause phenotypic variability and differential resistant response in tomato genotypes against early blight disease

Early blight disease caused by Alternaria solani is one of the dreadful diseases of the tomato. Existing cultural practices and fungicide applications are not enough to combat with the pathogen while, use of resistant cultivars is one of the most important ways to reduce disease damage. Currently, twenty-five tomato genotypes were screened out against the effect of early blight disease by artificially inoculating the plants with A. solani. The four tomato genotypes were kept in highly resistant (HR) group, 4 in resistant (RR), 5 in moderately resistant (MR), 4 in tolerant (TT), 5 in susceptible (SS) and 3 in highly susceptible (HS) on the basis of significant difference (LSD, p ≤ 0.05) in disease incidence, percent severity index and plant mortality. Growth attributes were significantly (p ≤ 0.01) decreased in SS and HS as compared to un-inoculated plants (control). Total phenolics, total protein content and activities of the antioxidant enzymes (catalase, peroxidase and polyphenol oxidase) were highly up-regulated in resistant groups than in susceptible groups linked with the induction of resistance against A. solani. The Pearson's correlation coefficient revealed a highly significant and very strong association between total phenolics and each biochemical component in HR and RR. The results of the current investigation indicated that phenolic compounds and activities of antioxidant enzymes in infected leaves could be used to assist the screening of resistant genotypes at early stages of early blight development.