ENVIRONMENTAL-EFFECTS ON THE INDUCTION OF WHEAT CHEMICAL DEFENSES BY APHID INFESTATION

The effects of temperature and photoperiod on the ability of wheat (Tr iticum aestivum L.) seedlings to show induced responses (increased acc umulation of hydroxamic acids, Hx) upon infestation by the bird cherry -oat aphid, Rhopalosiphum padi L. were evaluated under laboratory cond itions. Induction of Hx was significantly higher at lower temperatures . No such clear trend was found for the photoperiod effect. The signif icant effect of environmental conditions on growth rate of seedlings a nd the significant negative correlation between growth rate prior to i nfestation and induction of Hx suggested that environmental effects on induced responses were at least partially mediated through their effe ct on plant growth rate. After statistically uncoupling the effect of environmental conditions from the effect of plant growth rate, the eff ect of temperature on induction of Hx was no longer significant. There fore, the temperature effect was mediated by plant growth rate.