Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 24, 2011
Publication Date: July 15, 2011
Citation: Kolmer, J.A., Long, D.L., Hughes, M.E. 2011. Physiologic specialization of Puccinia triticina on wheat in the United States in 2009. Plant Disease. 95:935-940. Interpretive Summary: Wheat is attacked by the rust fungus called Puccinia triticina, which c1auses the disease wheat leaf rust. There are many different forms of the wheat leaf rust fungus that vary in their ability to attack different resistance genes in wheat. Every year the USDA-ARS Cereal Disease Laboratory makes collections of wheat leaf rust from the major wheat growing regions of the United States to determine which forms of the leaf rust fungus are present. In 2009, 41 different forms of the leaf rust fungus were found in the United States. The forms with virulence to leaf rust resistance gene Lr24 were widespread and very common in 2009. Leaf rust types with virulence to genes Lr17, Lr9, and Lr41 were also common in the Great Plains region, and forms with virulence to genes Lr11, Lr18, and Lr26 were common in the southeast states. These results can be used by wheat breeders and plant pathologists to help develop wheat cultivars that are very resistant to the leaf rust disease.
Technical Abstract: Collections of Puccinia triticina were obtained from rust-infected 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, California, and Washington State in order to determine the virulence of the wheat leaf rust population in 2009. Single uredinial isolates (591 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, Lr3a, Lr9, Lr16, Lr24, Lr26, Lr3ka, Lr11, Lr17a, Lr30, LrB, Lr10, Lr14a, Lr18, Lr21, Lr28, and a winter wheat line with Lr39/41. Forty-one virulence phenotypes were described. Virulence phenotypes MLDSD, TCRKG, and TDBGG were the three most common phenotypes. Phenotype MLDSD is virulent to Lr17 and Lr39/Lr41 and was widely distributed throughout the United States. 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. TDBGG is virulent to Lr24 and was found in both the soft red winter wheat and hard red winter wheat regions. Virulence to Lr21 was not found in any of the tested isolates. Virulence to Lr11, Lr18 and Lr26 increased in 2009 in the soft red winter wheat regions. Virulence to Lr17 and Lr39/Lr41 increased in the Great Plains region. 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.