The studied variables were: whole plant dry matter yield (WPDMY), stover dry matter yield (SDMY) and ear dry matter yield (EDMY). Trials were carried out in four environments and over two years. Analysis of Principal Effects and Multiplicative Interaction (AMMI) and Cruz Medina exact conditional test (ECT) (Heredity 69: 128-132, 1992) were employed. The first two axes of the principal component analysis (PCA) in AMMI model explained 89.7 % of the squares sum of the genotype-environment interaction for WPDMY. In ECT analysis a lack of adjustment of the multiplicative model for the genotype 4 was detected. Genotypes detected as unstable agreed with those obtained in the AMMI analysis. Environments 1 (A1) and 2 (A2) contributed in a greater extent to the genotype - environment interaction. The PCA biplot showed that crosses Population 1 x P2 (genotype 13) and Population 2 x P2 (genotype 14) expressed instability associated with environment 2 (A2), whereas crosses Population 1 x P1 (genotype 7) and Population 2 x P1 (genotype 8) had interaction with environment 4 (A4) (Figure 1). Instability in population 4, population 1 x P1 and population 1 x P2 for SDMY was detected. Population 4 and Population 3 x P2 were unstable for EDMY. In the same manner environment 3 was stable for EDMY whereas environment 4 was stable for SDMY. It can be concluded that high yielding crosses were bound to high instability and that per se materials behaved as stable. This information would be useful for subsequent selection directed towards one or the other component.

Figure 1. PCA biplot for WPDMY.

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