QUANTITATIVE TRAIT LOCI AND METABOLIC PATHWAYS - GENETIC-CONTROL OF THE CONCENTRATION OF MAYSIN, A CORN-EARWORM RESISTANCE FACTOR, IN MAIZESILKS

Interpretation of quantitative trait locus (QTL) studies of agronomic traits is limited by lack of knowledge of biochemical pathways leading to trait expression, To more fully elucidate the biological significa nce of detected QTL, we chose a trail that is the product of a well-ch aracterized pathway, namely the concentration of maysin, a C-glycosyl flavone, in silks of maize, Zea mays L. Maysin is a host-plant resista nce factor against the corn earworm, Helicoverpa tea (Boddie). We dete rmined silk maysin concentrations and restriction fragment length poly morphism genotypes at flavonoid pathway loci or linked markers for 285 F-2 plants derived from the cross of lines GT114 and GT119, Single-fa ctor analysis of variance indicated that the pi region on chromosome 1 accounted for 58.0% of the phenotypic variance and showed additive ge ne action. The pi locus is a transcription activator for portions of t he flavonoid pathway. A second QTL, represented by marker umc105a near the brown pericarp1 locus on chromosome 9, accounted for 10.8% of the variance. Gene action of this region was dominant for low maysin, but was only expressed in the presence of a functional pi allele, The mod el explaining the greatest proportion of phenotypic variance (75.9%) i ncluded pi, umc105a, umc166b (chromosome 1), r1 (chromosome 10), and t wo epistatic interaction terms, pi x amc105a and pi x r1. Our results provide evidence that regulatory loci have a central role acid that th ere is a complex interplay among different branches of the flavonoid p athway in the expression of this trait.