Establishment, Distribution, and Pathogenicity of Puccinia striiformis f. sp. tritici in South Africa.

Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici Eriks., has become an endemic disease of wheat (Triticum aestivum L.) in South Africa since it was first observed near Moorreesburg, Western Cape during August 1996. The main objectives of this study were to monitor the occurrence, spread, and the possible development of new variants of the stripe rust pathogen and the susceptibility of grass species to the pathogen. Results of surveys conducted during 1996 to 1999 revealed that rainfed wheat produced in the Western Cape, Eastern Cape, and the eastern Free State, as well as irrigated wheat produced in KwaZulu-Natal and the Free State, are most likely to be affected by stripe rust epidemics. Pathotype 6E16A- with virulence to Yr2, Yr6, Yr7, Yr8, Yr11, Yr14, Yr17, and Yr19 and pathotype 6E22A- with added virulence to Yr25 were detected. The occurrence of pathotype 6E22A- is currently restricted to KwaZulu-Natal and the Free State. Stripe rust isolates found on Hordeum murinum L. in the Western Cape were identified as pathotype 6E16A-, and both pathotypes 6E16A- and 6E22A- were collected from Bromus catharticus Vahl (= B. unioloides H.B.K.) in the eastern Free Sate. Urediospores from infections similar to stripe rust found on the grass species Dactylis glomerata L. (Eastern Cape), Poa pratensis L. (= P. bidentata Stapf; Western Cape), and P. annua and P. triviales L. (eastern Free State) failed to infect wheat cv. Morocco seedlings in the glasshouse. The possible role of grasses in the over-summering of the stripe rust pathogen has not yet been established. Stripe rust infections, however, have been found on summer-sown wheat in the south Western Cape during 1998, volunteer wheat growing in the summer and autumn months in the eastern Free State from 1998 to 2000, and on summer-sown wheat in Lesotho.