CHARACTERISTICS OF HYDROXAMIC ACID INDUCTION IN WHEAT TRIGGERED BY APHID INFESTATION

Hydroxamic acids (Hx) are natural products of Gramineae that are assoc iated with cereal resistance to pests. We aimed at characterizing the induction of Hx accumulation in seedlings of wheat, Triticum aestivum, by short-term infestation of the cereal aphid, Rhopalosiphum padi. A load of 25 aphids increased significantly the Hx levels in the infeste d primary leaf in comparison with control levels. Lower loads did not increase Hx concentration. Aphid infestation lasting 16 hr did not eli cit induction of Hx, even after a time-lag of 32 hr to allow the expre ssion of any induced response. Forty eight hours was the minimum durat ion of aphid infestation required to trigger Hx induction. The age of the infested tissue (the primary leaf) did not affect induction. Simil ar increases of Hx were found in unfolding, expanding, and totally exp anded primary leaves. It was determined that the regime of nutrient su pply (N-intensive nutritive solutions at low and high concentration) t o wheat seedlings had no effect on the magnitude of the aphid-induced Hx (N-based secondary metabolites). Results obtained are discussed in the framework of general theories of plant defense allocation.