The role of hydroxamic acids in conferring resistance to aphid pests of seedling maize (Zea mays)

Morse, Stephen (1990) The role of hydroxamic acids in conferring resistance to aphid pests of seedling maize (Zea mays). University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Hydroxamic acids (Hx) are chemicals found in a number of Gramineae including maize (Zea mays), and are thought to play a role in the resistance of the plants to various insect pests and pathogens. The most common Hx found in maize is 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA). The leaf content of Hx in the maize cultivar LG 11 was found to be strongly linked with leaf age. Newly emerging leaves had relatively high concentrations, while older, fully emerged, leaves had lower concentrations. The concentration of Hx in the tissue of LG 11 was generally found to increase when the plants were subjected to various forms of stress such as artificial damage and drought. In part the increase was due to a reduction in leaf growth, but in the case of artificial damage there did appear to be some synthesis. There was no clear link between the leaf Hx concentration of a number of maize varieties and the growth rate of Rhopalosiphum padi nymphs. However, there were higher levels of mortality when Sitobion avenae nymphs were caged on a variety with a relatively high Hx concentration compared to one with a lower concentration. Artificial damage, in the form of crushing, to maize leaves resulted in a higher mortality or a reduced growth rate of R. padi nymphs caged on those leaves. This effect could not be clearly linked to variation in the leaf concentration of Hx. With the use of high performance liquid chromatography (H.P.L.C.), DIMBOA was detected in the bodies, and DIMBOA glucoside in the honeydew of R. padi aphids feeding on maize. The latter result suggests that the DIMBOA glucoside may be translocated in the phloem of maize.

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