Hydroxamic acids in wheat in relation to cereal aphid biology and control

Nicol, David (1994) Hydroxamic acids in wheat in relation to cereal aphid biology and control. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Seedlings from worldwide sources of currently grown commercial varieties of wheat were analysed via HPLC for concentrations of hydroxamic acids (Hx). DIMBOA, the main hydroxamic acid in wheat, was present at levels between 1 and 8 mmol/kg fresh wt. This range encompasses levels previously reported to affect aphid performance.

The number of alate Sitobion avenae (Aphididae) settling on wheat seedlings in a multi-choice experiment, decreased with increasing levels of DIMBOA in the plant. However, the aphid Rhospalosiphum padi and apterous S. avenae were not significantly deterred from settling under these and other experimental conditions.

Nymphs of S. avenae clip-caged on wheat seedlings containing high levels of DIMBOA had a lower mean relative growth rate (MRGR) and were more susceptible to the pesticide, deltamethrin than were nymphs clip-caged on seedlings containing lower levels of DIMBOA. The LC₅₀ adjusted for nymphal weight was 91% lower on the resistant cultivar.

The levels of Hx in seeds, roots and leaves were analysed in germinating wheat seedlings from 0 - 7 days old. The maximal levels of DIMBOA found in roots of the three cultivars chosen ranged from 1.5 to 4.5 mmol/kg fresh wt. No Hx were found within the seed. Levels of DIBOA were expressed to a greater extent in roots than in the leaves.

Although levels of Hx in newly emerged flag leaves under greenhouse conditions and in field-grown seedlings were found to be significantly lower than in the leaves of seedlings that were grown under environmentally controlled conditions in a plant growth room the levels in the three plating groups were significantly positively related. In the greenhouse, this was true for newly emerged leaves at all growth stages. Therefore the screening of seedlings may provide a rapid and valuable method for predicting subsequent expression of Hx in newly emerged leaves at all growth stages of wheat. Levels of Hx in the ear were extremely low and between cultivars no significant differences in MRGR were indicated for nymphs of S. avenae on ears of flag leaves. However, MRGR was higher on ears than on flag leaves.

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