632 NORMAN E. BORLAUG 



THE DEVELOPMENT OF HIGH YIELDING BROADLY ADAPTED MEXICAN WHEAT VARIETIES 

 AND THEIR EFFECT ON WORLD WHEAT PRODUCTION 



From the outset in 1944 the Mexican Wheat Improvement Program, spon- 

 sored jointly by the Government of Mexico and The Rockefeller Foundation, 

 was organized to develop high-yielding varieties with good resistance to 

 diseases and which would be efficient in use of both irrigation water and 

 fertilizer. 



In order to shorten the time required to produce a new variety, 

 against the advice of the experts, our program pioneered extensively in 

 the growing of two generations of all breeding material each year. One 

 generation was grown during the winter, the commercial wheat crop season, 

 near Ciudad Obregon, Sonora, at about 28°N. latitude on the coastal plain 

 only a few feet above sea level. Near Toluca a second generation was 

 obtained by planting during mid-May at 8,500 feet and 18°N. latitude. 

 The Toluca site is characterized by heavy rainfall throughout the grow- 

 ing season and cool temperatures. Consequently severe epidemics of both 

 stem and stripe rust develop at this site every year. 



The process used in the Mexican program of moving segregating popu- 

 lations over 10 degrees of latitude and from near sea level to 8,500 feet 

 elevation, and its reverse, not only reduced by half the time required 

 to develop a new variety, but also simultaneously permitted the identifi- 

 cation of lines and the development of varieties with wide adaptation. 

 We now know that this, at least to a large extent, is the result of the 

 selection of lines that are insensitive to changes in day length and date 

 of planting, and hence are broadly adapted. Other selection pressures 

 also are undoubtedly acting under the very diverse conditions that 

 prevail at these two nursery sites (Borlaug, 1968). 



During the past 7 years CIMMYT has organized and coordinated The 

 International Spring Wheat Yield Nursery which is currently grown by 

 collaborators at more than 80 locations in the world. The varieties 

 included in this nursery include representatives of all of the principal 

 spring wheat producing areas of the world. During the past 7 years the 

 Mexican varieties have exhibited uniquely broad adaptation as measured 

 by high grain yield in many different countries of the world. Although 

 they were bred for use under irrigation with heavy fertilization, some 

 have shown outstanding performance under both fertilized and non-fertilized 

 irrigated and non-irrigated conditions. 



During the past 2 years s the Mexican dwarf wheat varieties have 

 been the principal catalyst involved in triggering off the green revolution 

 in Pakistan 3 India and Turkey (Borlaug, in press; Borlaug et al. s 1969). 

 They are now opening the breach to higher yield plateaus in a number of 

 other countries. It is the unusual breadth of adaptation, combined with 

 high genetic grain yield potential, dwarfness, a strong responsiveness 

 to fertilizers, and a broad spectrum of disease resistance that has made 

 the Mexican dwarf varieties so valuable to world agriculture. This 

 revolution in wheat production was not based, however, on the panacea 

 of the Mexican dwarf seed alone. It involved the transplant from Mexico 

 to Pakistan and India of a whole new production technology that makes 

 these varieties highly productive. Perhaps 75 to 80% of the research 

 done in Mexico in developing the package of cultural practices, including 

 fertilizer recommendations, was valid in Pakistan and India. Adaptive 

 research done in Pakistan, India, and Turkey while the imported seed was 

 being multiplied provided the necessary information to cover those gaps 

 where the Mexican data were not valid. 



