Elevated CO2 influences host plant defense response in chickpea against Helicoverpa armigera
Global atmospheric concentration of CO2 is likely to increase from 350 to 750 ppm over the next 100 years. The present studies were undertaken to understand the effects of elevated CO2 on enzymatic activity and secondary metabolites in chickpea in relation to expression of resistance to pod borer, Helicoverpa armigera. Fifteenday- old chickpea plants [ICCL 86111—resistant and JG 11—commercial cultivar] grown in the greenhouse were transferred to open-top chambers (OTC) and kept under 350, 550 and 750 ppm of CO2. Twenty neonates of H. armigera were released on each plant at 7 days after shifting the pots to the OTCs. Un-infested plants were maintained as controls. After 7 days of infestation, the activities of defensive enzymes [peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL) and tyrosine ammonia lyase (TAL)] and amounts of total phenols and condensed tannins increased with an increase in CO2 concentration in chickpea. The nitrogen balance index was greater in plants kept at 350 ppm CO2 than in plants kept under ambient conditions. The H. armigera-infested plants had higher H2O2 content; amounts of oxalic and malic acids were greater at 750 ppm CO2 than at 350 ppm CO2. Plant damage was greater at 350 ppm than at 550 and 750 ppm CO2. This information will be useful for understanding effects of increased levels of CO2 on expression of resistance to insect pests to develop strategies to mitigate the effects of climate change.