Maize silk maysin concentration and corn earworm antibiosis: QTLs and genetic mechanisms

Growth of the corn earworm (Helicoverpa tea Boddie), a major pest of maize (Zea mays L.), is inhibited by high concentrations of maysin, a C-glycosyl flavone, in maize silks. To advance understanding of the genetic control of silk maysin concentration and antibiosis to corn earworm, we conducted a quantitative trait locus (QTL) study in a population derived from a cross of high-maysin (GE37) and low-maysin (FF8) lines. Both lines have phenotypically identical, functional alleles at the pi. locus, a regulator of the biochemical pathway leading to maysin synthesis. We evaluated 250 (GE37 x FF8)F-23 families far (i) restriction fragment length polymorphisms at 121 loci, (ii) silk maysin concentrations in two locations tin Georgia and Missouri), and (iii) weight of corn earworm larvae grown on artificial diet containing oven dried silks. For maysin concentration in both locations, composite interval mapping revealed major QTLs in the asg20-whp1 interval of chromosome 2 and near the wx1 locus on chromosome 9; smaller effects were detected on chromosomes 1, 6, and 8. For larval weight, the largest QTL was detected in the asg2O-whp1 interval, and major effects were also associated with chromosomes 1 and 6. However, we found no effect on larval weight at wx1. Significant (P < 0.001) epistasis was observed for all traits. Our results suggest that whp1 on chromosome 2, a gene that encodes chalcone synthase and sm1, a silk-specific gene on chromosome 6, are candidate genes affecting maysin concentration and corn earworm larval weight in this population.