Helminthosporium blights of wheat: spot blotch and tan spot. Proceedings of an international workshop held at CIMMYT

Abstract

Over the last 30 ye~rs, in developing countries, the outstanding advances in wheat productivity attained by CIMMYT and its partners have contributed greatly to the well-being of millions of people. As growing numbers of farmers have taken advantage of new, superior wheat varieties, wheat has been introduced into warmer areas where it was not previously planted or has been grown in increasingly complex, intensive farming systems in the developing world's traditional wheat growing areas. These changing circumstances for wheat production have brought new challenges for farmers, including the increased incidence of helminthosporium blights of wheat: spot blotch, caused by Bipolaris sorokiniana, and tan spot, caused by Pyrenophora tritici-repentis. In South Asia's intensive rice-wheat cropping systems, particularly in the heavily populated eastern Gangetic Plains, spot blotch has become the major disease constraint. In reduced tillage cropping systems, tan spot is an increasingly important concern, as the pathogen survives on crop residues and alternate hosts. To complicate matters, these diseases may occur together in the field, where they are often very difficult to distinguish from one another. For this reason,-it is desirable to study their incidence and control together. The complexity of these nontraditional wheat diseases and of the conditions in which they occur makes it essential for us to seek a holistic approach for their control. Such an approach includes breeding for durable disease resistance; developing appropriate crop management practices, including nutrient applications; monitoring pathogen diversity; and applying recent advances in biotechnology to overcome disease losses. In addition, researchers need to develop a better understanding of the cropping systems and the many interactions that can influence the spread of disease. Better protocols for ensuring the production of healthy seed are needed as well. To strengthen research partnerships directed at reducing yield losses to these diseases, and to foster a more holistic view of potential strategies for disease control, CIMMYT organized an international workshop, Helminthosporium Blights of Wheat, at its headquarters in Mexico from 9 to 14 February, 1997. Sponsored by the Belgian Administration for Development Cooperation and CIMMYT, in close collaboration with the University of Louvain, Belgium, this workshop was an important component of a larger,- collaborative research project on nonspecific foliar pathogens of wheat. The meeting assembled key researchers from the national agricultural research systems of developed and developing nations to review recent advances in pathology and breeding for resistance to spot blotch and tan spot of wheat. Fifty-fo~ participants from 21 countries attended the workshop; participants represented most of the wheat-growing areas where tan spot and spot blotch limit yields. The workshop enabled researchers to bring each other up to date on the global incidence of foliar blights caused by B. sorokiniana and P. tritici-repentis, particularly in South Asia's ricewheat system and under reduced tillage. Research results were presented and discussed, future research collaborations defined, and networking activities strengthened, all with the goal of obtaining better disease control. This proceedings documents the results of a unique opportunity for CIMMYT scientists and their colleagues to exchange information on these two important diseases. The papers and workshop discussions presented here should provide a useful record for workshop participants. The proceedings also should prove to be a valuable reference for scientists who could not attend these meetings, researchers who work to reduce grain losses in the warmer production areas of developing countries, and their counterparts in.other parts of the world.