CIMMYTS APPROACH TO BREEDING FOR WIDE ADAPTATION

The wheat area in developing countries, including China, is around 100 million ha. To address the needs of these very diverse wheat growing areas, CIMMYT has defined 12 wheat mega-environments (ME). A ME is def ined as broad, not necessarily continuous often transcontinental area with similar biotic and abiotic stresses, cropping systems and consume r preferences. The factors describing each ME are presented. CIMMYT's breeding methodology is centered around the development of widely adap ted germplasm with high and stable yield across a wide range of enviro nments. Segregating populations are alternating screened in two divers e environments in Mexico. One key requirement is that all germplasm is tested under near optimum conditions for its yield potential. The sec ond one is multi-locational testing of advanced lines at sites that re present a given ME (key locations) and careful screening of germplasm for tolerance to abiotic and biotic stresses specific to that environm ent. This methodology has permitted the pyramiding of a large number o f multiple resistance genes for use against a wide spectrum of disease s and tolerance to abiotic stresses within each ME. In addition, the w idespread testing of lines allows the identification of traits which a re beneficial in several environments. Data from international nurseri es are used to further delineate environments within an ME. This appro ach has proven to be successful since around 70% of the spring wheat a rea in developing countries (excluding China) is planted to varieties derived directly or indirectly from CIMMYT germplasm. The performance of the bread wheat cultivar Pastor in international trials is given as an example for a wide adaptation.