Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/16/2002
Publication Date: 9/1/2002
Citation: BUSHMAN, B.S., SNOOK, M.E., GERKE, J.P., SZALMA, S.J., BERHOW, M.A., HOUCHINS, K.E., MCMULLEN, M.D. TWO LOCI EXERT MAJOR EFFECTS ON CHLOROGENIC ACID SYNTHESIS IN MAIZE SILKS. CROP SCIENCE. 2002. v. 42. p. 1669-1678. Interpretive Summary: The corn earworm is a serious pest of corn, particularly sweet corn, in the United States. A chemical compound found in the silks of corn called chlorogenic acid has potential as a natural, host-plant defense chemical against the corn earworm and other related pests. While most corn varieties have low levels of chlorogenic acid in silks, we have identified certain lines with levels of chlorogenic acid that should be sufficiently high to provide some measure of resistance. However, before chlorogenic acid can be used as a resistance mechanism, the genetic basis of the high chlorogenic acid trait needs to be determined. We used molecular and quantitative genetic approaches to identify the regions of corn chromosomes controlling chlorogenic acid synthesis in three corn populations. The results indicate a major role for two genes, one located on corn chromosome 1 and one located on corn chromosome 2. This result is important because it provides corn breeders, particularly sweet corn breeders, with the genetic tools needed to move the high chlorogenic acid trait into commercial materials to test if chlorogenic acid can provide resistance, thereby lessening our dependence on synthetic chemical control of this pest.
Technical Abstract: Chlorogenic acid (CGA) in maize (Zea mays L.) silks has been implicated in resistance to corn earworm (Helicoverpa zea: Boddie) with a mechanism similar to the flavone, maysin. However, the genetic basis of CGA synthesis is poorly understood. Our goal was to identify candidate loci affecting the biosynthesis of CGA using quantitative trait locus (QTL) analyses on three F2 populations: (A619 x Mp708)F2, (A619 x Mo6)F2, and (Mo6 x Mp708)F2. Chlorogenic acid and flavone contents in silks were measured, linkage maps generated, and significant loci identified with composite interval mapping (CIM) and ANOVA multiple-effects models for the three populations. Of the QTLs detected, two exerted major effects; one corresponding to the p1 locus, and the other was a novel locus we named qt12. The main effect of the functional allele at the p1 locus was to increase both CGA and flavones, while the positive allele at the qtl2 locus only increased CGA. An epistatic interaction between the p1 and qtl alleles in the (A619 x Mo6)F2 population caused an increase in CGA with a concomitant decrease in flavones. The rare ability of Mo6 and Mp708 to synthesize CGA in excess of flavones is primarily a result from the effects at the qt12 locus.