M. N. Rouse, USDA-ARS Cereal Disease Laboratory, 1551 Lindig Street, Saint Paul, MN 55108; and
C. A. Griffey and
W. S. Brooks, Department of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061
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 1990s, P. hordei pathotypes with virulence to resistance gene Rph7 caused average yield losses from 6 to 16% (3). ‘Doyce’ barley was released in 2003 and was described as being resistant to leaf rust (2). 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 (1). Previous methods used for inoculation, incubation, and pathotyping were followed (1). Infection types were scored on a 0 to 4 scale where 2 and below indicated resistance and 3 and above indicated susceptibility (4). The three isolates collected from Doyce barley displayed large pustules with infection types 3,3+ to cultivars Estate (Rph3) and Cebada Capa (Rph7). Avirulent isolates of P. hordei displayed infection types 0; to 0;1c to Estate and ;n to 0;1n to Cebada Capa (1). The data indicated that all three isolates were virulent to both barley leaf rust resistance genes Rph3 and Rph7. Though combined Rph3 and Rph7 virulence has been reported in the Mediterranean region, this is the first report of Rph3 virulence in North America. These isolates of P. hordei are virulent to important sources of resistance to barley leaf rust and threaten barley production in environments conducive for disease development in North America.
References: (1) W. S. Brooks et al. Phytopathology 90:1131, 2000. (2) W. S. Brooks et al. Crop Sci. 45:792, 2005. (3) C. A. Griffey et al. Plant Dis. 78:256, 1994. (4) M. N. Levine and W. J. Cherewick. U.S. Dept. Agric. Tech. Bull. 1056, 1952.