DIALLEL 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 o n acid soils. Maize yields are low on acidic soils because of toxiciti es of Al, Mn, and Fe, and deficiencies of P, Ca, Mg, and K. Acid-toler ant maize cultivars would be an environmentally friendly and relativel y inexpensive method for improving maize production on acidic soils. L ittle information is available in the literature on the magnitude of r eciprocal effects on yield and other agronomic traits when maize is gr own on acidic soils. A diallel study, involving eight segregating popu lations and their 56 reciprocal crosses, was conducted in five acidic- soil environments to determine relative importance of nuclear and cyto plasmic factors for yield, days to silk, ear height, ears per plant, a nd ear rot. Average (h) and specific (s(ij)) heterosis accounted for 6 5 and 31% of the total sum of squares for heterosis for yield. Populat ion heterosis effects (h(j)) for yield were not significant, suggestin g h(j) effects would be of little value in selecting populations for d eveloping superior hybrids. Specific heterosis effects were negative a nd significant (P < 0.05) for yield and ears per plant only for the cr oss of CMS 36 x ETO Blanco, suggesting a minor role for nonadditive ge ne effects in determining yield of specific cross combinations. The ab sence of reciprocal differences for all traits indicated that toleranc e to soil acidity was controlled by nuclear genes.