Presence of hydroxamic acids in the honeydew of aphids feeding on wheat seedlings, and its significance for plant resistance and virus transmission

Abstract

Cereal aphids damage wheat plants through direct feeding, promotion of fungal and transmission of viral diseases such as barley yellow dwarf virus (BYDV). Internal resistance factors in the plant may prevent virus transmission. Wheat contains hydroxamic acids (Hx), a family of compounds playing a key role in the defence of wheat seedlings against cereal aphids (Niemeyer, 1988). The main Hx in wheat is 2,4-dihydroxy-7-methoxy-1,4-benzoxazine-3-one (DIMBOA). It occurs in the intact wheat plant as a 2-β-O-D-glucopyranoside (DIMBOA-Glc), which is hydrolysed by endo-glucosidases when the plant is injured. Both DIMBOA and DIMBOA-Glc are aphid feeding deterrents and anti-biotics, but the glucoside is less effective than the aglucone. Wheat seedlings with higher Hx concentrations induce a decrease in aphid performance and a decrease in BYDV transmission (Givovich & Niemeyer, 1991). To assess the relative importance of DIMBOA and DIMBOA-Glc in modifying aphid behaviour and fitness, we have complemented previous analyses of Hx in aphid whole bodies with Hx analysis of honeydew.