Stability and genetic improvement of maize yield in Argentina

Summary Yield stability and the genetic improvement of maize (Zea mays L.) grain yield in the humid pampas of Argentina were evaluated.Stability parameters were computed for 15 varieties grown in 35 environments. To analyze genetic improvement of grain yield, data were obtained from trials grown in four locations and twelve years. Two locations represented the typical maize area, while the remaining two were considered marginal. Simple correlation and linear regression coefficients were computed to study the relationships between yield, stability parameters, number of days to 50% tassel emergence, and year of release. Genetic improvement of grain yield was analyzed from linear regression of the average yield of the three highest-yielding varieties (as percentage of the average yield of five common checks) on year of trial.Yield differed significantly among varieties. Significant variety x environment (linear) interaction was also detected. Significant linear relationships were found between regression coefficient for yield (stability parameter 1) and days to tassel emergence, stability parameter 1 and yield, year of release and days to tassel emergence, and year of release and stability parameter 1. Thus, newer maize varieties tended to flower later and had greater responsiveness to favorable environments than did older varieties. Yields have increased for both the typical and marginal areas, with average yearly increases of 114 and 182 kg/ha, respectively.Breeding programs with nurseries located in the typical maize area have raised yield potential in both areas studied. However, if present trends continue, future releases could prove inadequate in low-yielding or short season environments.