Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2008

Collections of Puccinia triticina were obtained from rust-infected wheat (Triticum aestivum) leaves provided by cooperators throughout the United States and from surveys of wheat fields and wheat breeding plots by USDA-ARS personnel in the Great Plains, Ohio River Valley, Southeast, and Washington State in order to determine the virulence of the wheat leaf rust population in 2008. Single uredinial isolates (730 in total) were derived from the collections and tested for virulence phenotype on lines of Thatcher wheat that are near-isogenic for leaf rust resistance genes Lr1, Lr2a, Lr2c, Lr3, Lr9, Lr16, Lr24, Lr26, Lr3ka, Lr11, Lr17, Lr30, LrB, Lr10, Lr14a, Lr18, Lr21, Lr28, and a winter wheat line with Lr41. Forty-eight virulence phenotypes were described. Virulence phenotypes TDBGG, TCRKG, and MLDSD were the three most common phenotypes. TDBGG is virulent to Lr24 and was found in both the soft red winter wheat and hard red winter wheat regions. Phenotype TCRKG is virulent to Lr11, Lr18, and Lr26 and is found mostly in the soft red winter wheat region in the eastern United States. Phenotype MLDSD is virulent to Lr17 and Lr41 and was widely distributed in the Great Plains. Virulence to Lr21 was not found in any of the tested isolates. Virulence to Lr11 and Lr18 increased in 2008 in the soft red winter wheat regions. Two separate epidemiological zones of P triticina in the soft red winter wheat region of the southern and eastern states and in the hard red wheat region of the Great Plains were described.