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

A set of 100 S1 plants were selected from a white and yellow maize population to generate both full-sib and half-sib progenies using North Carolina Design II (NCD II) mating scheme. The 250 progenies generated in each population were evaluated under artificial infestation with two borer species (Sesamia calamistis and Eldana saccharina) at two locations in two seasons to determine levels of genetic variability for improvement purposes. There were wide ranges for most of the traits studied in both maize populations. Plant height and grain yield were significantly reduced with mean grain yield loss being between 25 and 30%. In the white population, additive variance was larger than dominance variance for grain yield, days to 50% silking, stalk breakage and ear per plant, but for the yellow counterpart, additive variance was larger for plant height, ear per plant, leaf feeding and cob damage. None of the gene actions was important for dead heart. Narrow-sense heritability was low to moderate for the resistance parameters. It ranged from 1.45% for leaf feeding to 40.6% for stalk breakage in the white population, and from 3.80% for leaf feeding to 40.1% for cob damage in the yellow population. Heritability for grain yield was 37.6% in the white population but much lower (10.5%) in the yellow population. Although, heritability was low to moderate for the traits studied, the wide ranges and moderate additive variances obtained suggest that substantial genetic variability exist in the two maize populations for reasonable improvement to be made. Breeding scheme that capitalizes on both additive and dominance gene action would be effective for improving the populations for stem borer resistance and grain yield.