GENETICS OF TOLERANCE TO SOIL ACIDITY IN TROPICAL MAIZE

Maize (Zen mays L.) is grown on approximately eight million hectares o f 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 condu cted involving six soil-acidity tolerant and two susceptible segregati ng populations to identify superior germplasm to develop cultivars for acidic soils. The eight populations and their 28 crosses were evaluat ed in seven acidic soil environments. Tolerant populations averaged hi gher in yield (2.19 vs. 1.58 Mg ha(-1); P < 0.01), ears per plant (0.7 9 vs. 0.64; P < 0.05), and ear height (61.6 vs. 51.4 cm; P < 0.01), an d fewer in days to silk (68.8 vs. 69.7 d; P < 0.05) than the susceptib le populations. Mean squares of parents vs. crosses were highly signif icant for yield, ear height, and ears per plant, and significant for d ays to silk, indicating heterosis for these traits. Crosses between to lerant populations tended to yield higher (3.00 Mg ha(-1)) than those between tolerant and susceptible populations (2.40 Mg ha(-1)) and betw een susceptible populations (2.01 Mg ha(-1)). General combining abilit y (GCA) was highly significant for all traits, but specific combining ability (SCA) was significant only for ears per plant. Reciprocal recu rrent selection would be effective in developing superior cultivars fo r 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 end osperm cultivars.