Relationships among Bread Wheat International Yield Testing Locations in Dry Areas

Understanding the relationship among yield testing locations is important if plant breeders are to target germplasm better to different production environments or regions. To examine the relationship among international drought prone test sites, yield data from 122 locations, sown during a 6-yr period in CIMMYT's Semi-Arid Wheat Yield Trial (SAWYT) were analyzed. The shifted multiplicative model (SHMM) was used to group locations within each year and pattern analysis was employed to group those sites across years. Sites were grouped into regions representing the major zones of adaptation to drought according to CIMMYT's classification of mega-environments. Results spanning 1992 to 1997 were summarized on the basis of the number of times a particular site or region clustered with the target region, which was expressed as a fraction or percentage of the total number of possible groupings. Results indicated that the Centro de Investigaciones Agricolas del Noroeste (CIANO), CIMMYT's primary drought evaluation location, clustered with locations in South Asia, specifically India and Bangladesh. However, the number of clusters between CIANO and other Mexican locations with West Asia, Africa, and South America were fewer. This result suggests that the residual moisture stress generated at CIANO under limited irrigation conditions, while relevant to equivalent sites in the Indian Subcontinent, does not predict performance at locations where different stress patterns predominate. Associations among sites and regions, determined on the basis of clustering, ranged from weak (7% of total possible groupings in the case of Mexico and the Southern Cone of South America) to relatively strong (60% for Mexico and Bangladesh). Clusters of sites repeated in more than one year indicated two dominant groups, one for South Asian locations (including CIANO, Mexico) and another containing primarily South American sites.