A Multivariate Method for Classifying Cultivars and Studying Group × Environment × Trait Interaction

Classification methods are used in genetic resource conservation and plant breeding. The two‐stage Ward‐Modified Location Model (Ward‐MLM) clustering strategy defines initial groups by the Ward method and the MLM is then used to improve those groups. The three‐way clustering strategy considers the same trait measured in different environments as different variables (environment–trait combination), so that the resulting clusters of cultivars have a small group × environment interaction (GEI) for all the traits included in the study. An important component of the GEI is the imperfect genotypic correlation or crossover interaction (COI). This study used the three‐way Ward‐MLM clustering strategy in three different data sets with the objectives of (i) evaluating the ability of the Ward‐MLM methodology for clustering cultivars into groups with low COI, (ii) obtaining a graphical representation of the variables in a low dimensional scatter plot produced by the multidimensional scaling method (MDS) in which the GEI of continuous and categorical traits and environments can be visualized, and (iii) studying how the relationship between a pair of traits changes across environments. The three‐way Ward‐MLM strategy produced groups of cultivars with low levels of COI. The increment of the correlation coefficient values between groups with respect to the total correlation coefficients indicated that the groups formed by the three‐way Ward‐MLM strategy comprised subsets of individuals that had similar trait responses across environments.