eaf and stem rusts are the major diseases limiting both wheat production and the longevity of high-yielding varieties in Egypt, Ethiopia, Sudan and Yemen. The diseases are a truly regional problem because of the ease with which infection is spread by rust spores carried by the wind over long distances within and between countries.
Chemical control is expensive and may not be justified if infection levels turn out to be low. In a bid to find other ways of controlling and limiting the rapid spread of disease, a wheat rusts regional network was established in which Egypt plays the leading technical role, and Ethiopia, Sudan, Yemen, ICARDA and CIMMYT (International Maize and Wheat Improvement Center) are partners. The network is one of six problem-solving networks within the Regional Networks Project established under ICARDA's Nile Valley and Red Sea Regional Program, and is financially supported by the Government of the Netherlands.
        To assess the threat from rusts, Burkard mechanical spore traps were installed at a number of locations across the region. Rust trap nurseries were also established at 22 sites throughout the region where monitoring could be carried out on the status of leaf and stem rust pathotypes and on spore movement. The nurseries included wheat rust monogenic lines, wild relatives, check varieties, and high-yielding promising lines and cultivars.
        As a result of this monitoring program, 28 different leaf rust races (8 in Egypt, 2 in Sudan, 15 in Ethiopia, and 3 in Yemen) and 30 stem rust races (13 in Egypt, 10 in Ethiopia, and 7 in Yemen) were identified between 1995/96 and 1998/99. Their frequencies of occurrence in the respective countries and across the region were recorded. The performance of leaf and stem rust isogenic lines was tested and effective resistant genes for each country and for the region were identified. For the region, these were Lr's 21, 17, 3Ka, 30, 11, and 21 and Sr's Gt+, 7b, 5, 8a, and 30.
        These genes are now being incorporated into high-yielding but previously-susceptible cultivars in each country. A breeding program is also under way in all four countries to develop high-yielding, adapted, resistant cultivars. Five commercial wheat cultivars and advanced lines were found to be resistant to the prevailing leaf rust races in Egypt, 16 in Ethiopia, 18 in Sudan, and 25 in Yemen, while 15 cultivars had good resistance to stem rust. Monitoring from 1993 to 1999 revealed nine cultivars performing well against both types of rust in the region. In 1998/99, out of the 48 tested cultivars and lines against leaf and stem rusts, 18 cultivars showed multiple disease resistance.
        The spore traps are helping researchers to under-

stand the way in which the rusts spread. It has been established that leaf rust inoculum in Egypt is exogenic--originating from outside the country--and its pathway is from north to south, while in Ethiopia it is endogenic, or permanently present. In Sudan, it also seems that the primary inoculum comes from outside the country, possibly from Yemen, given the presence of spores all year round, or from other African neighboring countries.
        Although the question of stem rust primary inoculum needs further investigation, it appears that the inoculum in Ethiopia and Yemen is present all year round due to the two-cycle cropping system, and that in Egypt it may come from the north or from the south depending on wind direction. Rust spores were found throughout the year, with even the smallest quantity of inoculum having the potential to be the source of an epidemic, given the right conditions. Armed with knowledge of disease source, farmers can choose suitable resistant varieties and avoid monoculture which can promote breakdown to resistance. Delayed planting may help, and fungicides may be the best option under conditions of high rainfall or irrigation.
        The Regional Networks Project established by ICARDA's Nile Valley and Red Sea Regional Program aims through complementary efforts to utilize expertise, human resources, and infrastructure efficiently in the member countries. A multidisciplinary and multi-institutional approach is used to strengthen basic and applied research on problems arising from biotic and abiotic stresses facing the production of food legumes and cereals in the four countries. Research is jointly planned but conducted and reported by national scientists.
        Each network is headed by a lead country based on the country's comparative advantage with respect to the expertise of its national scientists in that area. Basic research is conducted in that country, and the outcome of research is verified through adaptive research under local conditions in the other participating countries. ICARDA provides technical support, germplasm, and training, and facilitates research coordination, logistic support and administration.