Disease Note

First Report of a Puccinia graminis f. sp. tritici Race with Virulence for Sr24 in South Africa. J. le Roux, Small Grain Centre, Bethlehem 9700, South Africa. Plant Dis. 69:1007. Accepted for publication 22 July 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-1007b.

A single dominant gene, Sr24, originally transferred from Agropyron elongatum (Host) Beauv. to wheat (Triticum aestivum L.) chromosome 3DL, conferred resistance to Puccinia graminis Pers. infections for many years worldwide. During the 1984 season, two resistant cultivars, SST 44 and Gamka, possessing Sr24 became infected with stem rust in commercial fields. Seedling infection types for Sr24 testers to the new isolate (2SA100) were: 3 Ag 1 (3⁺), 3 AG 3 (3⁺), Agent (2^{+ +}3), BtSr24Ag2 (33⁺), and Gamka (3⁺). Although the adult plant reactions of Agent, SST 44, and Gamka were susceptible, uredia on Agent appeared smaller than those on SST 44 and Gamka. Wheat stem rust isolate 2SA100 has the following avirulence/virulence formula to the differential Sr genes: 7b, 9e, 9g, 13, 15, 25, 26, 30, 31, 32, 36/5, 6, 7a, 8, 9a, 9b, 9d, 10, 11, 16, 17, 18, 19, 20, and 24.