Physiologic specialization of Puccinia triticina on wheat in the United States in 2015

Authors: KOLMER, JAMES; HUGHES, MARK

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2017
Publication Date: 12/1/2017
Citation: Kolmer, J.A., Hughes, M.E. 2017. Physiologic specialization of Puccinia triticina on wheat in the United States in 2015. Plant Disease. 101:1568-1973.

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 2015, 60 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. 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 obtained from wheat fields and breeding plots in the Great Plains, Ohio River Valley, and southeastern states, were tested for virulence in 2015 in order to determine the virulence of the wheat leaf rust pathogen population in the United States. Single uredinial isolates (526 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 2015, 60 virulence phenotypes were described in the United States. Virulence phenotypes MBDS, MBTNB, and TBBGS were the three most common phenotypes. Phenotype MBDSD is virulent to Lr17 and Lr39, and was most common in the hard red winter wheat area of the southern Great Plains. Phenotypes MBTNB is virulent to Lr11, and was most common in the soft red winter wheat region of the southeastern states and Ohio Valley. Phenotype TBBGS is virulent to Lr39, which is present in the hard red winter wheat cultivars, and Lr21, which is present in the hard red spring wheat cultivars. Isolates with virulence to Lr11 and Lr18 were most common in the southeastern states and Ohio Valley region. Isolates with virulence to Lr21 and Lr39 were most common in the hard red wheat region of the southern and northern Great Plains.