Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2006

Collections of Puccinia triticina were obtained from rust-infected leaves provided by cooperators throughout the United States and from surveys of wheat fields and nurseries in the Great Plains, Ohio River Valley, southeast, California, and Washington State in order to determine the virulence of the wheat leaf rust population in 2006. Single uredinial isolates (718 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 Lrl, Lr2a, Lr2c, Lr3a, Lr9, Lrl6, Lr24, Lr26, Lr3ka, Lr11, Lr17a, Lr30, LrB, Lr10, Lrl4a, Lr18, Lr2, and Lr28 and winter wheat lines with genes Lr41 and Lr42. In the United States in 2006, 56 virulence phenotypes were found. Virulence phenotypes TDBJG, TDBGG, and TDBJH were among the four most common phenotypes and were all virulent to resistance gene Lr24. These phenotypes were found throughout the Great Plains region. Phenotype MLDSD with virulence to Lr9, Lrl7, and Lr41was also widely distributed in the Great Plains. In the soft red winter wheat region of the southeastern states, phenotypes TCRKG and MBRKG with virulence to genes Lr11, Lr26, and Lr18 were among the common phenotypes. Virulence phenotypes with virulence to Lrl6 were most frequent in the spring wheat region of the northern Great Plains. Virulence to Lr21 was not found in any of the tested isolates.