GENETICS OF TOLERANCE TO SOIL ACIDITY IN TROPICAL MAIZE

Maize (Zen mays L.) is grown on approximately eight million hectares of acidic soils, where yields are low because of the toxicity of Al and Mn and deficiency in Ca, Mg, and P. Maize cultivars tolerant to soil acidity would increase yields on such soils. A diallel study was conducted involving six soil-acidity tolerant and two susceptible segregating populations to identify superior germplasm to develop cultivars for acidic soils. The eight populations and their 28 crosses were evaluated in seven acidic soil environments. Tolerant populations averaged higher in yield (2.19 vs. 1.58 Mg ha(-1); P < 0.01), ears per plant (0.79 vs. 0.64; P < 0.05), and ear height (61.6 vs. 51.4 cm; P < 0.01), and fewer in days to silk (68.8 vs. 69.7 d; P < 0.05) than the susceptible populations. Mean squares of parents vs. crosses were highly significant for yield, ear height, and ears per plant, and significant for days to silk, indicating heterosis for these traits. Crosses between tolerant populations tended to yield higher (3.00 Mg ha(-1)) than those between tolerant and susceptible populations (2.40 Mg ha(-1)) and between susceptible populations (2.01 Mg ha(-1)). General combining ability (GCA) was highly significant for all traits, but specific combining ability (SCA) was significant only for ears per plant. Reciprocal recurrent selection would be effective in developing superior cultivars for acidic soils and should include populations 90SA-3 and 90SA-4 or CMS-36 for yellow endosperm cultivars and 90SA-6 and 90SA-7 for white endosperm cultivars.