Diallele analysis of acid-soil tolerant and intolerant tropical maize populations

Acid soils cover approximately 30% of the global ice-free land area. Nearly 26 million hectares of maize (Zea mays L.) is already planted on acid soils. Maize yields are low on acidic soils because of toxicities of Al, Mn, and Fe, and deficiencies of P, Ca, Mg, and K. Acid-tolerant maize cultivars would be an environmentally friendly and relatively inexpensive method for improving maize production on acidic soils. Little information is available in the literature on the magnitude of reciprocal effects on yield and other agronomic traits when maize is grown on acidic soils. A diallel study, involving eight segregating populations and their 56 reciprocal crosses, was conducted in five acidic-soil environments to determine relative importance of nuclear and cytoplasmic factors for yield, days to silk, ear height, ears per plant, and ear rot. Average (h) and specific (s(ij)) heterosis accounted for 65 and 31% of the total sum of squares for heterosis for yield. Population heterosis effects (h(j)) for yield were not significant, suggesting h(j) effects would be of little value in selecting populations for developing superior hybrids. Specific heterosis effects were negative and significant (P 0.05) for yield and ears per plant only for the cross of CMS 36 x ETO Blanco, suggesting a minor role for nonadditive gene effects in determining yield of specific cross combinations. The absence of reciprocal differences for all traits indicated that tolerance to soil acidity was controlled by nuclear genes