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Title: First Detection of Puccinia hordei virulence to barley leaf rust resistance gene Rph3 and combination with virulence to Rph7 in North America

item Rouse, Matthew
item GRIFFEY, CARL - Virginia Polytechnic Institution & State University
item BROOKS, WYNSE - Virginia Polytechnic Institution & State University

Submitted to: Disease Note
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2013
Publication Date: 6/15/2013
Citation: Rouse, M.N., Griffey, C.A., Brooks, W. 2013. First Detection of Puccinia hordei virulence to barley leaf rust resistance gene Rph3 and combination with virulence to Rph7 in North America. Disease Note [online]. 97(6):838. Available:

Interpretive Summary: An economically significant disease of barley in the United States Mid-Atlantic region and California is barley leaf rust. Currently resistant barley varieties are used to control this disease. A barley variety in Virginia called "Doyce" was previously resistant to barley leaf rust. We found high infection on Doyce during the 2010-2012 growing seasons. Collections of the barley leaf rust fungal pathogen from "Doyce" were isolated to determine if there is a new strain of the fungal pathogen. After testing barley lines with known barley leaf rust resistance genes, we found that the fungal pathogen is different than any previously known barley leaf rust pathogens in the United States because it is virulent to the barley leaf rust resistance gene "Rph3". The isolates virulent to "Rph3" were also virulent to other barley leaf rust resistance genes that are used to protect barley from leaf rust. These new isolates, characterized as pathotype 3757, threaten barley production in the United States in environments conducive for barley leaf rust such as the Mid-Atlantic region. Barley breeders will use this information in selecting barley breeding lines with leaf rust resistance mediated by genes other than Rph3. Barley growers and consultants will use this information by scouting previously resistant varieties of barley for potential increased use of fungicides to protect barley from yield losses to the new pathotype of the barley leaf rust pathogen.

Technical Abstract: Barley leaf rust, caused by Puccinia hordei Otth., has been problematic in United States barley, Hordeum vulgare L., production in the Mid-Atlantic coast region and California. During the early 1990’s P. hordei pathoytpes with virulence to resistance gene Rph7 caused average yield losses from 6-16%. "Doyce" barley was released in 2003 and was described as resistant to leaf rust. Initially in April 2010 and subsequently in spring 2011 and 2012, high severities and infection responses were observed on experimental plots of "Doyce" in Warsaw and Blacksburg, Virginia. Three single uredinial isolates of P. hordei were derived from collections made from "Doyce" barley. The isolates were characterized for virulence to barley leaf rust resistance genes by inoculating at least two replicates of a barley leaf rust differential set including 12 Rph genes. Previous methods used for inoculation, incubation, and pathotyping were followed. All three isolates were virulent to both Rph3 and Rph7 and were classified as octal pathotype 3757. The virulence/avirulence formula for pathotype 3757 is Rph1, Rph2, Rph3, Rph4, Rph6, Rph7, Rph8, Rph9.i, Rph10, Rph11/Rph5, Rph9.z. Though combined Rph3 and Rph7 virulence has been reported in the Mediterranean region, this is the first report of Rph3 virulence in North America. Pathotype 3757 of P. hordei is virulent to important sources of resistance to barley leaf rust including genes Rph3 and Rph7 and threatens barley production in environments conducive for disease development in North America.