Maize (Zea mays L.) is grown on approximately eight million hectares of acidic soils, where yields are low because of the toxicity of AI and Mn and deficiency in Ca, Mg, and P. Maize cultivars tolerant to soil acidity would increase yields on such soils. A diailel 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 beterosis 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.

Key words AI and P levels to assess AI toleranee Brazilian and USA inbred lines Plant measurements for AI toleranee Zea mays Summary Maize (Zea mays L.) inbred lines were grown in nutrient solution with different levels of AI and P to study their genetie variability for AI toleranee. Plant measurements for determining inbred line responses to AI wc re also evaluated. The best traits to assess maize for AI toleranee were seminal and adventitious root lengths.Brazilian maize inbred lines were mare tolerant to AI for the traits measured than USA inbred lines when grown in nutrient salutian. Most inbred lines tested showed deereased root lengths, but a few Brazilian lines were not affeeted by the Allevels used. At higher Allevels most Brazilian lines were not affeeted as severely as the USA lines. Toleranee of the inbred lines to AI was inereased by indusion of P in nutrient solutions. The greatest AI-indueed deerease in root length generally oeeurred at the lowest P level. The eombination of 185 j1mol AI L -1 and 45 j1mol P L -1 in nutrient solutions was the best eombination of AI and P to evaluate maize genotypes for AI toleranee in this study.

Backcrosses Dominance effects Epistasis F2 generations General and specific combining abilities Heterosis ReIative seminal root length Zea mays '-' Summary The inheritance of AI tolerance in maize (Zea mays L.) was studied in nutrient solution. Analysis of relative seminal root lengths of six generations (P" P2, F" F2, BC" and BCJ derived from crosses between tolerant and non-tolerant inbred !ines showed that additive gene effects contributed most to genetic variation for AI tolerance of the materiaIs included in this study. Dominance effects accounted for only half as much variation as did additive effects. Effects of epistasis contributed !ittle compared to other gene effects. The frequency distributions of plants within the F2 generations were continuous, unimodal, and typical for quantitatively inherited traits. There was some tendency for non-tolerance to be dominant over tolerance, but it was not consistent. In a diallel cross among inbred lines, lhe analysis of F, crosses indicated that lhe variance for general combining ability explained most of the variation, but specific combining abi!ity was statistically sigriificant in each case.

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