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Physiologic Specialization and Epidemiology of Wheat Stem Rust in East Africa. D. E. Harder, Assistant Professor, University of Manitoba, Canada Department of Agriculture, 25 Dafoe Road, Winnipeg 19, Manitoba; G. R. Mathenge(2), and L. K. Mwaura(3). (2)(3)Assistant Agricultural Officers, Plant Breeding Station, Njoro, Kenya. Phytopathology 62:166-171. Accepted for publication 29 August 1971. DOI: 10.1094/Phyto-62-166.

Nine new races of Puccinia graminis tritici were differentiated on new host cultivars in East Africa in 1969 and 1970. There was new virulence on wheat cultivars commonly grown in East Africa, and on cultivars used as sources of stem rust resistance. Most of the identified resistance genes are ineffective against East African races, but a good reservoir of resistance is available. Similar races were found in Ethiopia, Kenya, and Tanzania, suggesting the exchange of or a common source of inoculum in the region. Spore traps at Njoro and Kitale in Kenya, and at Njombe in Tanzania, showed that airborne rust inoculum is present throughout the year. This is attributed to wide variations in cropping seasons in East Africa. No grass species were found which were susceptible to wheat stem rust.