Expression of different mechanisms of resistance to insects in groundnut under field conditions
Host plant resistance is an important component of pest management, and information on contribution of different mechanisms of resistance is important for developing cultivars with resistance to the target pests. Therfore, we studied the contribution of different components of resistance in five groundnut genotypes to three insect species occurring in India under field conditions. Plant damage by the larvae of Helicoverpa armigera, Spodoptera litura, and leafhoppers (Empoasca kerri) was evaluated visually on a 1 – 9 damage rating (DR) scale (1 being <10 % leaf damage, and 9 being >80 % leaf damage). Further, the activities of various plant defensive enzymes [peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), superoxide dismutase (SOD), ascorbate peroxidase (APX), lipoxygenase (LOX) and catalase (CAT)], and the amounts of total phenols, condensed tannins, hydrogen peroxide (H2O2), malondialdehyde (MDA) and proteins were also recorded. The genotypes ICGV 86699, ICGV 86031, ICG 2271 and ICG 1697 suffered lower leaf damage by H. armigera and S. litura (DR 2.6 – 3.2) and E. kerri (DR 2.0 - 3.2) as compared to JL 24 (DR 7.2 and 6.0, respectively). ICGV 86699, ICGV 86031, ICG 2271 and ICG 1697 exhibited greater enzymatic activity, and had more amounts of phenols, condensed tannins, hydrogen peroxide and proteins than the susceptible check, JL 24. There was a positive association between leaf damage and the activity of the defensive enzymes, and the amounts of phenols, condensed tannins and H2O2. These results suggested that the plant defensive enzymes such as POD, PPO, LOX, PAL, SOD, APX and CAT were involved in genotypic resistance to insects, and the resistant genotypes accumulated phenols, condensed tannins, and H2O2 to impart resistance to insects. This information will be useful for developing groundnut genotypes with resistance to insects for sustainable crop production.