EN
Rapid generation of superoxide radicals and accumulation of H₂O₂ is a characteristic early response of plants following perception of insect herbivory signals. Induction of oxidative burst on account of herbivory triggers various defense mechanisms in plants. Response of superoxide and H₂O₂-metabolizing enzymes and secondary metabolites in nine pigeonpea genotypes to Helicoverpa armigera feeding was investigated. Out of nine, four genotypes were found to be moderately resistant, three were intermediate and two were moderately susceptible. In general, H. armigera infestation resulted in increase in superoxide dismutase activity, H₂O₂ and phenolics content and decrease in catalase (CAT) activity in leaves, developing seeds and pod wall of pigeonpea genotypes. Peroxidase activity was found only in leaves. Among genotypes, the increase in phenolic constituents was found greater in moderately resistant genotypes than in moderately susceptible genotypes; this might determine their contribution in providing resistance to genotypes against H. armigera infestation. The capability of moderately resistant genotypes to maintain relatively lower H₂O₂ content and higher CAT activity in pod wall and developing seeds also appeared to determine resistance of genotypes towards H. armigera. Expression of resistance to H. armigera was found to be associated with a negative correlation of H₂O₂- metabolizing enzymes and phenolics with pod damage as well as with negative association between CAT activity and H₂O₂ content. A positive correlation found between H₂O₂ content and pod damage suggested the accumulation of H₂O₂ in response to pod borer attack. In addition, correlation analysis also revealed a positive association between CAT, phenolic compounds and DPPH radical scavenging activity following pod borer attack; this indicated their contribution in resistance mechanisms against H. armigera herbivory.