A diallel study of stalk rot resistance in elite maize and its interaction with yield

Stalk rot reaction of maize (Zea mays L.) and its effect on yield was studied using 12 elite inbred parents (A619, A632, B73, H60, H93, H96, Mo17, Oh7B, Pa91, Va17, SS419, Va85) and all possible single crosses among them. The diallel study was conducted at Warsaw, Virginia in 1985. The experimental design was a split-plot with two stalk rot pathogens (Diplodia maydis and Fusarium moniliforme) and a control being the three whole plots and the inbreds described above and their single cross hybrids being the sub-plots. Plots were inoculated with the pathogens approximately three weeks following silking. Stalk rot scores and yield was taken four weeks following inoculation. Analyses of variance and combining ability analyses were performed on stalk rot scores and grain yield.

There were no significant differences between the two pathogens for mean stalk rot score, but both were significantly higher in score than the control. Differences among the whole plots for mean yield were not significant. Hybrid/line by pathogen interactions were not significant for yield or stalk rot scores, indicating that the inbreds and their hybrids performed consistently across the pathogens and control. The estimates of GCA and SCA effects for stalk rot score both were significant with the GCA effects being the greater. This should indicate that stalk rot reaction would respond readily to selection in a breeding population. Per plant yields were not affected by the stalk rot treatments. Two Virginia lines, Val7 and Va85, were found to have both high yield and high levels of resistance to stalk rot, and should be good candidates for a breeding program stressing stalk rot resistance.