Response of foreign barley cultivars to barley yellow mosaic virus at different sites in China

About 90 barley cultivars mostly of European or Japanese origin, were grown for 2-5 years at eight sites in China where barley yellow mosaic virus was known to occur. The sites were selected because they had previously been used to screen breeding lines and some differences between them in cultivar response had been suspected. ELISA tests showed that symptomless plants were not infected by the virus and the proportions of plants with symptoms were therefore recorded as a measure of susceptibility. European cultivars carrying the ym4 gene, which confers resistance to the common European strain, were usually resistant at two sites but susceptible at the others, but one (cv. Energy) was resistant at all sites. Eleven of the Japanese cultivars showed differential responses between sites but there was no correspondence with strains recognized in Japan. There are probably several distinct Chinese strains but further experiments would be needed to identify them. The Japanese cultivars Chosen, Hagane Mugi, Iwate Mensury 2 and Mokusekko 3 seem to be resistant to all known virus strains and are probably the most useful for plant breeders.