'Plant Breeding: Sustaining the Future' Abstracts of the XVIth EUCARPIA Congress, Edinburgh, Scotland, 10-14 September 2001 INTERNATIONAL WHEAT BREEDING S. RAJARAM, M.P. REYNOLDS CIMMYT, Apdo. Postal 6-641, Mexico 06600, D.F., Mexico

The International Maize and Wheat Improvement Center (CIMMYT) has been involved in international wheat breeding since 1966, but its research built on the experience of its predecessor organization, the Rockefeller Foundation’s program in Mexico, initiated in 1944. Its early successes include the international provision of high yielding, semidwarf, photoperiod-neutral, and widely adapted wheat germplasm that was highly resistant to stem rust. These successes were the product of a clearly defined shuttle breeding program proposed and led by Dr. N.E. Borlaug. The resulting varieties led to the Green Revolution in Asia, although fertilizers and optimum water use technology were equally important.

The last 25 years of the 20^th century were critical in maintaining the momentum of the Green Revolution through the expansion of modern semidwarfs to all corners of the globe, especially in the less developed world. We would like to highlight successes which though less heralded were critical to international wheat breeding.

1. Large-scale expansion of wheat genetic diversity through the spring x winter wheat crossing scheme, which produced the Veery varieties. Descendants of those varieties yield up to 10 t/ha in the Yaqui Valley, Sonora, Mexico, an optimum environment. In the last 25 years, national agricultural research systems (NARS) in developing countries released at least 500 cultivars that trace their origins to CIMMYT. We’ll cite just two examples of the impacts of those varieties combined with superior production technology. The average wheat yield in the Yaqui Valley in 1970 was 3 t/ha. By 2000 it had risen to 6 t/ha. In the Indian Punjab, the average yield was 1.5 t/ha in 1970. By 2000, it had increased to 4.2 t/ha. These data confirm not only the stability of Green Revolution varieties, but also the fact that wheat productivity per unit area has continued to improve.

2. In the last 25 years, high yielding CIMMYT wheats were fortified with minor genes for rust resistance (all three rusts) along with fusarium head blight, septoria tritici, BYDV, tan spot and Karnal bunt. The slow rusting concept was used to select minor genes for leaf and stripe rusts. Dilatory disease development was used to score other non-rust pathogens. Consequently, most CIMMYT germplasm provided to NARS now possesses horizontal (non-specific) resistance to those diseases. This has avoided boom-and-bust production cycles due to pathogen shift. Indeed, in the last 25 years, major rust epidemics have been prevented, except for the stripe rust epidemic recorded in Middle East in the 1990s.

3. In the early 1980s we started breeding for tolerance to drought, heat, and Al⁺⁺⁺ toxicity. Our strategy has been to combine stress tolerance in germplasm already tailored for high yield performance and fortified with adequate disease resistance. Perhaps many of you in the audience would disagree with our philosophy, and of course we do not discourage others to do differently. However, you should know that the application in plant breeding of the above conceptual framework is feasible. We were surprised to find that the high yielding base per se and adaptation to drought, heat, and Al⁺⁺⁺ toxicity are not negatively correlated; hence these adaptability genes can be easily combined in high yielding germplasm. The varieties Baviacora (for drought) and Seri 82 (for high temperatures) are excellent examples of these genetic combinations.

4. We believe that the achievements of the last 25 years will remain highly significant during the first 25 years of the 21^st century. However, wheat demand and supply vis-à-vis population growth will require further shift in the breeding paradigm. Some relevant issues:

A. Restructuring Plant Types and Exploiting Heterosis in Wheat
CIMMYT has launched two more breeding schemes besides the traditional programs described above. One scheme is focused on breeding a type of wheat dubbed AGROPOLITETRA by one of us (S. Rajaram), based on a novel genetic combination of the following germplasm:
1. Agrotriticum (Canada)
2. Polonicum (Poland)
3. Tetrastichon (Yugoslavia)
4. Morocco (Morocco)
5. Triticale (Mexico)
6. Semidwarf wheats (Mexico

 The original combinations were created by Mr. Ricardo Rodriguez, now a retired scientist. Agropolitetra wheats will have intermediate tillering capacity (up to 10 tillers), long spikes (30 cm), high fertility (up to 200 grains), broad leaves and thick stems as their basic visual morphology. Most of these characters have already been combined, except for good and plump grains, especially in the short growing period of the Yaqui Valley, Sonora, Mexico.

 The exploitation of heterosis in wheat is not new; however, most previous attempts have failed due to the high costs of seed production. Recent hybrids produced at CIMMYT by Dr. Belgin Cukadar have yielded up to 21% higher than the best commercial cultivars.

 Agropolitetra and hybrid wheats should enter yield trials in 2001. We are optimistic that trial results will bear out the promise of the new wheats.

B. Fortifying Wheat Grain with Micronutrients
 We hope to launch a breeding program aimed at increasing the Fe and Zn content in wheat grain. These micronutrients are lacking in high yielding wheat varieties widely grown in Asia, where Fe and Zn deficiencies are common, especially among women and children in marginal areas whose diet is based mainly on cereal grains. There is good variability in wheat germplasm for high Fe and Zn content. However, we also plan to select for low phytase levels, which will make Fe and Zn in wheat grain easily bioavailable to the human population. It should be noted that the phytic acid content of CIMMYT germplasm has declined in the last 50 years.

C. Application of Transgenics in Farming Systems
 Although transgenic wheats are politically and socially discouraged in many countries, and will perhaps be kept away from agriculture for a long time to come, this technology may be the most powerful means at our disposal for increasing the productivity of wheat-based systems. However, we should point out that our attempts at this stage are at the research level only. We will strive to transform our most widely adapted genotypes for various traits such as herbicide resistance, industrial quality genes, and durable disease resistance.