Environmental stratifications for soybean cultivar recommendation and its consistency over time

Stratification of environments is a strategy to capitalize genotype x environment (GxE) interaction, which can optimize the process of assessment and cultivar recommendation, increasing productivity in a target environmental population. The objective of this study was to assess environmental stratification methods based on the analysis of GxE interaction, to identify consistent agronomic zones across time for soybean. Grain yield data of inbred lines from three maturity groups (early, medium, and late) were used. Lines and cultivars were tested in regional variety trials during three growing seasons at eighteen locations in the tropics of Central Brazil. Three methods were applied to stratify the environments. The first was based on joint analyses of variance for all the pairs of locations within each growing year. The second was based on a distance measure between each pair of locations, which was related to the GxE interaction estimated via additive main effects and multiplicative interaction analysis. The third was based on the approach of winning genotypes. The stratification results from the first two methods were not consistent across the growing seasons. However, the winning genotype approach provided consistent environmental stratification across years. From locations used in the genotypic assessment, three environmental clusters were identified for the early and medium maturity groups of soybean, and four clusters for the late maturity group. The use of different genotypic sets across years reinforces the predictive value of the environmental stratification established.