Identification of heterotic groups for the tolerance of maize (Zea mays L.) for tropical acid soils

Thirty-eight maize (Zea mays L.) hybrids, from crossings of 19 inbred tropical lines with two heterotic testers and five control varieties, were evaluated in 1999 and 2000 for their tolerance for acid soils at two sites (Ebolowa and Nkolbisson) in Cameroon. The acid soils at Ebolowa and Nkolbisson are related to aluminum and manganese toxicity, respectively. the objectives of this study were to assess the effects of the genes of some inbred lines on acid soil in order to classify them into heterotic groups and identify the best hybrid for each type of soil. The results for the eight environments tested showed that the effect on yield of the two types of acid soils was associated with both additive and nonadditive gene action, with the latter predominant for the soil with aluminum toxicity and the former for the soil with manganese toxicity. Length of the seminal root was affected much more by additive gene action in both types of acid soil. Six hybrids and ten progenitors were identified as most tolerant of acid soil with aluminum toxicity. Six other hybrids and five progenitors showed good potential for use on soils with manganese toxicity. Two hybrids were effective on both soil types: Cam inb gp1 17 x 87036 and Entrada 29 x 87036. The best progenitors for both types were: Cam mb gp1 17, ATP S4 25 W, CMLci-IDR-STR, 87036 M131 and CML 357. When this study was concluded, two heterotic groups were proposed for each type of acid soil. The composition of these groups was different for each. For the soil with aluminum toxicity, length of seminal root can be an efficient indicator for identifying genotypes tolerant of acid soil. It was not efficient, however, for the soil with manganese toxicity. We concluded that the mechanism controlling tolerance to acid soils differs between types of acidity.