PEDIGREE SELECTION FOR IMPROVED PARTIAL RESISTANCE TO COMMON LEAF RUST IN SWEET CORN

Common leaf rust (Puccinia sorghi Schw.) of maize (Zea mays L.) can produce large yield losses in commercial sweet corn fields planted to susceptible hybrids. Greater levels of partial resistance could reduce the need for protective fungicides to control rust epidemics. Our objective was to determine whether pedigree selection was effective in improving partial resistance to common leaf rust. Three sugary (su) sweet corn breeding populations were inbred to the F-5 with selection for rust resistance in each generation. Plants grown from remnant seed from the F-2 to F-5 were examined in four field environments for disease severity at five weekly periods beginning one week before anthesis until anthesis + 21 d under artificial disease epidemics. The F-5 Lines from each of the three populations developed 27, 19, and 49% lower mean disease severity than the original F-2 populations three weeks after anthesis. There were significant correlations (r(2) = 0.77-0.95) between ratings of mean disease ratings for any two of the five sample periods. There was also a significant correlation (r(2) = 0.72-0.91) between mean disease severity and ratings derived from the worst leaf in the plot over five disease sampling periods.