Associations among international CIMMYT bread wheat yield testing locations in high rainfall areas and their implications for wheat breeding

A good understanding of how the target environments for a breeding program differentiate the germplasm with respect to yield is crucial and allows plant breeders to better target their germplasm. To determine the relationships among high rainfall yield testing locations, yield data from 8 yr of CIMMYT's High Rainfall Wheat Yield Trial (HRWYT) were analyzed by shifted multiplicative model (SHMM) and incremental sum of squares (ISS) classification analyses to group sites within and across years. In the cumulative cluster analysis, about half of the sites clustered into a group characterized by increasing temperature toward maturity. The SHMM analysis identified several sites with high overall association with other sites around the world, and which can be considered as good predictors of global yield performance within the high rainfall megaenvironment. These are autumn-sown locations, which fall into the biggest group of the cumulative cluster analysis with increasing temperature during the growing season. On the other hand, remarkably low associations with global yield ranking were shown for Sta. Catalina (Ecuador) and CIMMYT's primary high rainfall yield-testing location at Toluca (Mexico), which in contrast experience decreasing temperatures toward maturity. Although excellent sites for disease screening, this analysis shows that they do not associate well with the world's high rainfall wheat growing areas for yield.