During August 1996, stripe (yellow) rust, caused by Puccinia
striiformis f. sp. tritici, was observed for the first time on bread wheat (Triticum aestivum) in the Western Cape, South Africa. Ensuing surveys during the growing season indicated that stripe rust occurred throughout most of the wheat-producing areas in the winter rainfall regions of the Northern, Western, and Eastern Cape provinces. The disease was also observed on irrigated wheat in the summer rainfall area south of Kimberley. Stripe rust was most severe in the Western Cape, where prolonged cool and wet conditions favored epidemic development and necessitated extensive and often repeated applications of triazole fungicides. Due to spike infection and destruction of foliage, significant losses in grain quantity and quality occurred in certain fields. Avirulence/virulence characteristics of 32 stripe rust isolates, collected from commercial wheat fields, trap nurseries, and triticale, were determined on 17 standard differential wheat lines and seven supplementary testers supplied by C. R. Wellings, Plant Breeding Institute, Cobbitty, Australia. All isolates were representative of one pathotype, characterized by avirulence to Chinese 166 (Yr1), Vilmorin 23 (Yr3), Moro (Yr10), Strubes Dickkopf, Suwon 92/Omar, Clement (Yr2,9), Triticum aestivum subsp. spelta var. album (Yr5), Hybrid 46 (Yr4), Reichersberg 42 (Yr7), Heines Peko (Yr2,6), Nord Desprez (Yr3), Carstens V, Spaldings Prolific, Heines VII (Yr2), Federation*4/Kavkaz (Yr9), and Avocet-S/Yr15, and by virulence to Kalyansona (Yr2), Heines Kolben (Yr2,6), Lee (Yr7), Compair (Yr8), and Federation 1221. Cultivars Trident (Yr17), Avocet-R (YrA), and Selkirk (YrSk) appeared heterogeneous for stripe rust reaction. The pathotype resembled race 6E16, previously detected in East and North Africa, the Middle East, and western Asia. Pathotype identity was confirmed at IPO-DLO, Wageningen, using one South African isolate of P. striiformis f. sp. tritici. In view of the rapid dispersal of the pathogen during 1996, susceptibility of several high-yielding cultivars, and favorable climatic conditions in many wheat-growing areas, stripe rust is considered potentially damaging to South African wheat production. Field observations and seedling tests have shown, however, that certain cultivars are resistant to the introduced pathotype. At present the genetic basis of this resistance is largely unknown.
