Sources of Resistance in Barley toRhynchosporium secalis

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Abstract
Nearly 18,000 entries from the USDA [US Department of Agriculture] world barley collection were evaluated in the field for resistance to R. secalis. Maximum disease exposure was provided by repeated inoculations of a mixture of 5 California [USA] isolates with known combined abilities of pathogenicity on previously identified sources of resistance. No distinct pattern of origin of resistance was revealed. Nine entries from 6 countries (France, Japan, USA, Israel, Ethiopia and Wales [UK] showed no symptoms, but 273 entries with representatives of 3 spp. (Hordeum distichum L. emend Lam, H. vulgare L. emend Lam, and H. irregulare Aberg and Wiebe) showed high levels of resistance. All other entries were susceptible to the range of pathogenicity of the inoculum employed. Resistant entries included 2-rowed and 6-rowed spring, winter, and facultative types. Results nearly identical to those in the field were obtained when more than 2000 of the entries were evaluated in the greenhouse. Use of newly identified sources of resistance should include consideration of the presence and frequency of specific races, because these differ throughout the world.