Defensive Responses in Groundnut Against Chewing and Sap-Sucking Insects

Induced resistance is one of the important components of host plant resistance to insects. We studied the induced defensive responses in groundnut genotypes with different levels of resistance to the leaf defoliator Helicoverpa armigera and the sap-sucking insect Aphis craccivora to gain an understanding of the induced resistance to insects and its implications for pest management. The activity of the defensive enzymes (peroxidase, polyphenol oxidase, phenylalanine ammonia lyase, superoxide dismutase, ascorbate peroxidase, and catalase) and the amounts of total phenols, hydrogen peroxide, malondialdehyde, and proteins were recorded at 6 days after infestation. Induction of enzyme activities and the amounts of secondary metabolites were greater in the insect-resistant genotypes ICGV 86699, ICGV 86031, ICG 2271, and ICG 1697 infested with H. armigera and A. craccivora than in the susceptible check JL 24. The resistant genotypes suffered lower insect damage and resulted in lower Helicoverpa larval survival and weights than those larvae fed on the susceptible check JL 24. The number of aphids was significantly lower on insect-resistant genotypes than on the susceptible check JL 24. The results suggested that groundnut plants respond to infestation by H. armigera and A. craccivora in a similar way; however, the degree of the response differed across the genotypes and insects, and this defense response is attributed to various defensive enzymes and secondary metabolites.