Response of Japanese wheat varieties to three pathotypes of wheat yellow mosaic virus

Yellow mosaic disease, caused by wheat yellow mosaic virus (WYMV), is one of the most serious diseases of winter wheat ( Triticum aestivum L.) in Japan. WYMV pathotype I is distributed mainly in western and central Japan, pathotype II in northern Japan, and pathotype III on a part of the southern island of Japan. Major resistance genes and quantitative trait loci for WYMV were previously identified on wheat chromosomes 2DL, 3BS, and 5AL. We evaluated a total of 165 modern Japanese wheat varieties, released by the Ministry of Agriculture, Forestry and Fisheries, for response to the three pathotypes in field trials, and genotyped them using microsatellite markers associated with the three WYMV resistance genes. Based on the data, we propose a model for the relationship between the three resistance genes and WYMV pathotypes. The results strongly suggest that the resistance conferred by the gene on 5AL has broken down with emergence of pathotype III, which may be derived from pathotype I.