Expected responses to selection for resistance to the pink stem borer (Sesamia calamistis Hampson) and the sugarcane borer (Eldana saccharina Walker) in two maize populations

Progenies from two maize populations, one white-grained (DMR ESR-W) and the other yellow (DMR ESR-Y) were evaluated under artificial infestation with two borer species (Sesamia calamistis and Eldana saccharina) in two seasons to predict responses and correlated responses to selection for resistance to stem borers. Correlations between grain yield and most agronomic parameters were significant. There were negative correlations between grain yield and damage parameters in both maize populations. The highest genotypic correlation coefficient was observed between grain yield and stem tunneling (rg = -0.52) in DMR ESR-Y, and with stalk breakage (rg = -0.67) in DMR ESR-W. A Rank Summation Index (RSI) generated using plant aspect, grain yield, stem tunneling, leaf feed¬ing and tolerance had positive phenotypic correlations with damage parameters, but negative relationship with agronomic traits. All agronomic parameters including grain yield will increase with selection. Grain yield increase of about 210 kg/ha will be obtained per generation in DMR ESR-W using two seasons to complete a cycle, but a relatively low increase (73 kg ha-1) is expected in DMR ESR-Y. Response from single trait selection was better than from RSI in DMR ESR-Y, but reverse was the case in DMR ESR-W. Correlated responses to selection showed that direct selection for most of the traits would be better than indirect selection through any other trait. Appreciable progress is expected from selection for improvement of the maize populations for resistance to the two borer spe¬cies, although progress from selection may be slow.