Occurrence and Pathogenicity of Puccinia hordei on Barley in South Africa

Although leaf rust, caused by Puccinia hordei, is considered an important disease of barley (Hordeum vulgare) and regularly reaches epidemic proportions, pathogenic variability has never been studied in South Africa. From 1994 to 1997, only one pathotype (SAPh 3231) was identified with virulence to resistance genes Rph1, Rph4, Rph5, Rph10, and Rph11. During 1998, a second pathotype (SAPh 7321) was identified, differing from pathotype SAPh 3231 only in virulence to Rph12. Pathotype SAPh 7321 increased rapidly in the area where it was first detected, resulting in localized epidemic outbreaks in 1999. The reactions of various South African cultivars and breeding lines toward these pathotypes were determined, and the presence of Rph12 was postulated for B93/4, Krona, Optic, Prisma, and SSG 532. Rph genes showed varying degrees of temperature sensitivity, with none of the known genes displaying major changes in their phenotypes except Rph8, which was less effective at higher temperatures. Eight accessions of two wild Hordeum spp. occurring abundantly in the barley growing regions were found to be either weak or nonhosts for P. hordei.