GENETIC VARIABILITY FOR STEM BORER RESISTANCE IN TWO ADAPTED EARLY-MATURING MAIZE (Zea mays L.) POPULATIONS

Stem borers are among the major biotic stresses limiting the grain yield of maize, an important cereal crop in Africa. Breeding for multiple resistance to maize stem borers has been reported to be a promising method of control. Understanding the genetic variability of crop populations will help in improving them for pest resistance. Thus, genetic variability for dual resistance to two stem borer species were determined in a white (DMR ESR-W) and a yellow (DMR ESR-Y) maize populations to provide information required for improving their levels of resistance to the borers. Two experiments were conducted. In Experiment 1, a set of 100 S1 plants of DMR ESR-W were selected to produce 250 full-sib and half-sib progenies using the North Carolina Design II (NCD II) mating scheme. The progenies with six checks were evaluated under artificial infestation with two borer species (Sesamia calamistis and (Eldana saccharina) at Ibadan, and non-infested conditions at Ibadan and Ikenne in 2008 and 2009 using Randomized Incomplete Block Design with two replications. Experiment 2 was with DMR ESR-Y and the same methodology was used. In both experiments, days to 50% anthesis and silking, plant and ear height, plant and ear aspect, ear length and grain yield were measured. Resistance was measured according to levels of leaf feeding damage, dead heart, stalk breakage, cob damage and stem tunneling. Analyses of variance for NCD II were conducted to estimate genetic variances and Narrow-Sense Heritability (NSH). Correlation coefficients were determined and partitioned into direct and indirect effects. Predicted responses to selection were estimated to measure expected genetic gains. Correlated response was used to determine traits that could hasten selection progress. Tests of significance were conducted at p < 0.05.