Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/1998
Publication Date: N/A
Citation: N/A Interpretive Summary: The corn earworm is an important insect pest of corn production in the U.S. and Latin America. We are determining the genetic basis for the synthesis of a chemical called maysin that when present in corn silks is toxic to the corn earworm. In this study we showed that the synthesis of maysin and a related compound called apimaysin are largely independent changing our view of the biochemical pathway that gives rise to these chemicals. The relationship of synthesis of these two compounds and their effect on corn earworm larval growth implicate other chemicals in silks as also having important roles in toxicity to the corn earworm. These studies increase our effectiveness in breeding for corn earworm resistant corn varieties.
Technical Abstract: In maize (Zea mays L.), the presence of C-glycosyl flavones in silk tissues results in host-plant resistance (i.e., antibiosis) to corn earworm larvae (Helicoverpa zea (Boddie)). The C-glycosyl flavones are distinguished by their B-ring substitutions, with maysin and apimaysin being the di- and mono-hydroxy forms, respectively. Herein we examine the genetic mechanisms underlying the synthesis of maysin and apimaysin and the corresponding effects on corn earworm larvae growth. Using a F2 population of 316 individuals derived from the cross between the inbred lines GT114 and NC7A, genotyped at 89 marker loci, we found a single QTL for maysin synthesis, rem1, which accounted for 55.3% of the phenotypic variance and a single QTL for apimaysin synthesis, pr1, which explained 64.7% of the phenotypic variance. Because the maysin QTL did not affect apimaysin synthesis, the apimaysin QTL did not affect maysin synthesis, and maysin was not made at the expense of apimaysin and vice versa, our results suggest that the synthesis of these closely related compounds occur independently. The two single QTLs, rem1 and pr1, were involved in a significant epistatic interaction for total flavones. The maysin and apimaysin QTLs were significant QTLs for corn earworm antibiosis, accounting for 14.1% (rem1) and 14.7% (pr1) of the phenotypic variation. An additional QTL, represented by umc85 on the short arm of chromosome 6 affected antibiosis (R2 = 15.2%) but did not affect the synthesis of the C-glycosyl flavones. Poor correlations of maysin r = -0.38), apimaysin (r = 0.48) and total flavone levels (not correlated) with larval weight suggest that maysin and apimaysin are produced at the expense of other antibiotic compounds.