Physiologic specialization of Puccinia triticina on wheat in the United States in 2012

Authors: Kolmer, James; Hughes, Mark

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2014
Publication Date: 8/1/2014
Citation: Kolmer, J.A., Hughes, M.E. 2014. Physiologic specialization of Puccinia triticina on wheat in the United States in 2012. Plant Disease. 98:1145-1150.

Interpretive Summary: Wheat is attacked by the rust fungus called Puccinia triticina, which causes the disease wheat leaf rust. There are many different forms or races 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 the wheat leaf rust fungus from the major wheat growing regions of the United States to determine which forms of P. triticina are present. In 2012, 74 different forms of the leaf rust fungus were found in the United States. The forms with virulence to the resistance genes in the commonly grown hard red winter wheats were widespread throughout the eastern states and the Great Plains region. The races with virulence to the genes present in the soft red winter wheats were found in the eastern states and the Ohio Valley region. The most commonly grown hard red winter wheat cultivars and soft red winter wheat cultivars are susceptible to the most common leaf rust races found in the regions where these wheat cultivars are grown. It will be important to develop wheat cultivars with new combinations of leaf rust resistance genes in the winter wheat regions. In 2012 a race with virulence to many spring wheats in Minnesota and North Dakota increased, making these wheats very susceptible to leaf rust. The results from the annual virulence survey are 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 wheat fields and breeding plots by USDA-ARS personnel and cooperators in the Great Plains, Ohio River Valley, southeastern states, and Washington State in order to determine the virulence of the wheat leaf rust population in 2012. Single uredinial isolates (501 total) were derived from the collections and tested for virulence phenotype on 20 lines of Thatcher wheat that are near-isogenic for leaf rust resistance genes. In 2012, 74 virulence phenotypes were described in the United States. Virulence phenotypes TNBGJ, TCRKG, and MBTNB were the three most common phenotypes. Phenotype TNBGJ is virulent to Lr39/41 and was widely distributed throughout the hard red winter wheat region of the Great Plains. 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. Phenotype MBTNB is virulent to Lr11 and was also found mostly in the soft red winter wheat region. The frequency of isolates with virulence to Lr39/41 which is present in many hard red winter wheat cultivars in the Great Plains region continued to increase. Isolates with virulence to Lr21, which is present in many hard red spring wheat cultivars also continued to increase in frequency in the northern Great Plains region.