Abstract
An additive main effect and multiplicative interaction (AMMI) model was used to analyse data from two sets of open-pollinated maize (Zea mays L.) varieties (early- and late-maturing varieties). Each of the two sets was separately assessed for grain yield in 18 locations representative of the main agro-ecologies in Nigeria. Mean grain yields for the two sets of data were 2.32 and 2.72 t ha-1 for early- and late-maturing varieties, respectively, giving a yield advantage of 17.24% of the late-maturing varieties over the early-maturing varieties. Location effects accounted for 76.42 and 78.71% of the total variation in the early open-pollinated and late open-pollinated varieties, respectively. Variation among the maize varieties in each of the two sets, although very small (1.16 and 0.66% for early and late open-pollinated varieties, respectively), was, however, significant. Significant genotype x location (GL) interactions effects were also observed, and they accounted for 7.39 and 5.61% of the total sums of squares (SS) for the early and late open-pollinated varieties, respectively. The first three interactions of the principal component analyses were significant in the two sets and together were responsible for 81.76 and 78.76% of the SS due to GL interaction for the early and late open-pollinated varieties, respectively. Most of the early open-pollinated varieties were similar and stable in maize grain production. The most stable and superior late-maturing maize varieties were Suwan-2-SR and Acr 92 TZE Comp 5-WD. For the two sets of data, similarity of sites was related to their geographic proximity. Eight sites within mangrove and forest agro-environments consistently formed a cluster in each of the two sets of data indicating that these sites induced similar adaptation patterns on the open-pollinated maize varieties. It is therefore suggested that testing sites in the mangrove-forest agro-environments be reduced to four. Likewise, two testing sites may also suffice for the locations in the mid-altitude agro-environment.
