GENETIC VARIANCES FOR TOLERANCE TO SOIL ACIDITY IN A TROPICAL MAIZE POPULATION

Soil acidity reduces yield on approximately 10% of the maize (Zea mays L.) area in developing countries. Information on the inheritance of a cid-soil tolerance would help scientists choose more appropriate metho ds for efficient breeding of tolerant cultivars. We used a North Carol ina Design II mating system to study the relative importance of additi ve (V-A) and dominance (V-D) variances and their interactions with env ironments in the 'SA-4' tropical maize population. One-hundred-sixty S -1 lines were randomly assigned to 20 sets of eight lines. Within each set, four lines were arbitrarily designated as males and four as fema les. Each male was crossed with each female in the set, providing 16 f ull-sib families. The 20 sets, with 16 full-sib families each, were fi eld-planted in two replications in one non-acid- and four acid-soil en vironments during 1992 in Colombia and Brazil. Across acid soils, V-D was significantly greater than V-A for yield (0.22 vs. 0.09) and days to silk (2.33 vs. 1.35) and lower for ear height (23.93 vs. 37.48), ea rs/plant: (0.0013 vs. 0.0018), and ear rot (4.86 vs. 13.65). Heritabil ities, based on half-sib family means, averaged 0.39+/-0.14 for yield, 0.43+/-0.14 for days to silk, 0.66+/-0.13 for ear height, 0.47+/-0.14 for ears plant(-1), and 0.48+/-0.14 for ear rot across the acid-soil environments. Magnitudes of V-A and V-D and their interactions with en vironments indicated that reciprocal recurrent selection, using multil ocation testing, would be effective for developing improved maize cult ivars for acid soils.