Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2010.

Collections of Puccinia triticina were obtained from rust-infected leaves provided by cooperators throughout the United States and from wheat fields and breeding plots by United States Department of Agriculture-Agricultural Research Service personnel and cooperators in the Great Plains, Ohio River Valley, southeastern states, Oregon, and Washington State in order to determine the virulence of the wheat leaf rust population in 2010. Single uredinial isolates (537 total) were derived from the collections and tested for virulence phenotype on 19 lines of 'Thatcher' wheat and a winter wheat line that are near-isogenic for 20 leaf rust resistance genes. In 2010, 38 virulence phenotypes were described in the United States. Virulence phenotypes MLDSD, TDBJG, and TCRKG were the three most common phenotypes. Phenotype MLDSD is virulent to Lr17 and Lr39/Lr41 and was widely distributed throughout the United States. Phenotype TDBJG 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 was found mostly in the soft red winter wheat region in the eastern United States. Virulence to Lr21 was found for the first time in North America in isolates collected from spring wheat cultivars in North Dakota and Minnesota.