LAUSR

2647 The Yaqui Valley in Sonora, Mexico, is agro-climatically representative of a major ecological zone (megaenvironment) comprised of irrigated wheat areas with very low rainfall. In the Yaqui Valley, there are approximately 225,000 ha of land under an irrigation system where canals are used to deliver water from a series of reservoirs for use by farmers as flood or furrow irrigation. Other major representative irrigated wheat areas with very low rainfall are the Indus Valley in Pakistan, the Gangetic Valley in India, and the Nile Valley in Egypt. Around 32 million hectares of wheat (producing 42.7% of the total wheat production in the world) are grown in this type of irrigated environment in the developing world. The wheat-growing periods in these areas are associated with temperate climates; however, sudden rises in temperature before and after flowering are common and salinity problems may occur where drainage is poor (Meisner et al., 1992). The yield expansion during the Green Revolution era of the 1970s was the result of sowing varieties with improved disease resistance and increased yield potential, together with greater use of agricultural inputs. The Yaqui Valley has been the site of the wheat breeding operations of the International Maize and Wheat Improvement Center (CIMMYT) for more than 50 yr. The bread and durum wheat yields in the Valley have progressed at a remarkable rate, but the rate of increase has slowed in the last decades. However, the gap between the high bread wheat (BW) and durum wheat (DW) yields on research stations, and the low yields in farmers’ fields in the Yaqui Valley has been, on average and over the years, about 3 t ha–1 or more. It should be pointed out that farm size in the Yaqui Valley ranges from medium to large, from less than 10 ha to more than 150 ha (average farm size: about 20 ha); the most common farm size is about 10 ha. The grain yield gap between CIMMYT’s main wheat breeding experiment station in the Yaqui Valley and farmers’ fields in the Yaqui Valley stimulates the practice of evaluating advanced bread and durum wheat lines from CIMMYT’s Global Wheat Modeling Genotype × Environment Interaction Using a Factor Analytic Model of On-Farm Wheat Trials in the Yaqui Valley of Mexico