Variation of Hydroxamic Acid Content in Maize Roots in Relation to Geographic Origin of Maize Germ Plasm and Resistance to Western Corn Rootworm (Coleoptera: Chrysomelidae)

Abstract

Thirty-three lines of maize, Zea mays L., from different latitudinal geographical regions were surveyed for concentrations of hydroxamic acids. All root extracts were found to contain four major hydroxamic acids: 2,4-dihydroxy-7-methoxy-I,4-benzoxazin-3-(4H)-one (DIM BOA), 2,4-dihydroxy-7,8-dimethoxy-l,4-benzoxazin-3(4H)-one (DIM2BOA), 2-hydroxy-7-methoxy-l,4-benzoxazin-3(4H)-one (HMBOA), and 6-methoxy-benzoxazolinone (MBOA). The range in hydroxamic acid levels between various maize lines was >30-fold, which may provide the variation necessary for selection of lines with high levels ofhydroxamic acids in breeding programs. There was a trend showing that differences in concentrations of hydroxamic acids were associated with the different geographical groups, and that the intermediate temperate region (ITR) group had higher levels of all individual compounds, especially DIM BOA equivalents. Several maize lines commonly used in resistance studies of western corn rootworm, Diabrotica virgifera virgifera LeConte, were analyzed for hydroxamic acid levels. Corn rootworm-resistant inbreds such as SD-10 had both a larger root system and a higher hydroxamic acid concentration. A positive though weak correlation between concentration of DIM BOA in maize roots and in maize leaves was found. Seven maize lines with various hydroxamic acid levels were grown and infested by western com rootwoml larvae under controlled environmental conditions. Larval development parameters, including survival, weight, and head capsule width, were significantly and negatively correlated with hydroxamic acid levels in maize roots. These results suggest that hydroxamic acids may in some instances contribute to the resistance of maize to western corn rootworm larvae, and that hydroxamic acids may be useful as a phytochemical indicator of resistance in screening programs.