Two loci exert major effects on chlorogenic acid synthesis in maize silks

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 F-2 populations: (A619 x Mp708)F-2, (A619 X Mo6)F-2, and (Mo6 x Mp708)F-2. 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 a novel locus we named qtl2. The main effect of the functional allele at the pi locus was to increase both CGA and flavones, while the positive allele at the qtl2 locus only increased CGA. An epistatic interaction between p1 and qtl2 alleles in the (A619 x Mo6)F-2 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 qtl2 locus.