Physiologic specialization of Puccinia triticina on wheat in the United States in 2010

Authors: Kolmer, James; LONG, DAVID - Retired ARS Employee; Hughes, Mark

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/29/2012
Publication Date: 6/1/2012
Citation: Kolmer, J.A., Long, D., Hughes, M.E. 2012. Physiologic specialization of Puccinia triticina on wheat in the United States in 2010. Plant Disease. 96:1216-1221.

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 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 2010, 38 different forms of the leaf rust fungus were found in the United States. The forms with virulence to the resistance gene 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 are grown. There was not a major change in the most common races in the hard red winter wheat region of the Great Plains or the soft red winter wheat region in the eastern states and Ohio Valley region. Leaf rust races with virulence to a resistance gene in many of the hard red spring wheats in Minnesota and North Dakota were found for the first time in 2010. These new races will likely increase and cause increased yield losses due to leaf rust in future years. It will be important to develop wheat cultivars with other combinations of leaf rust resistance genes in the spring wheat region. These results 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 surveys of wheat fields and wheat breeding plots by USDA-ARS 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 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. 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 is 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. Virulence to Lr11, Lr18 and Lr26 decreased in 2010 in the soft red winter wheat regions. The frequency of isolates with virulence to Lr16, Lr24, Lr17 and Lr39/Lr41 were relatively unchanged from 2009 in the Great Plains region. Two separate regional populations 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.