The possibility of breeding white-grained wheats tolerant to pre-harvest sprouting under Japanese humid weather conditions is discussed. New genetic dormancy sources, such as, AUS1408, 8019R1 and RyuuMai7, were evaluated for seed dormancy in different weather conditions. Some white-grained dormant wheats showed a strong dormancy similar to that of red-grained dormant wheats in a greenhouse trial, in the field their dormancy expression was much less than the red wheats. Three populations involving crosses with these new sources for winter wheat breeding were examined under repeated selection for seed dormancy. Some dormant white-grained lines, as judged under glasshouse conditions, were developed. Again the level of dormancy in these lines was not sufficient compared to red dormant varieties in field trial. In order to develop truly superior dormant white-grained materials, one population involving crosses with two dormant varieties, AUS1408 and 8019R1, was examined under repeated selection. From these materials we succeeded in breeding lines that had not only a good dormancy but also showed adaptation to Japanese weather conditions, including earliness, scab resistance and good seed appearance. However again the dormancy of these lines in field trial was not sufficient compared to that of red wheats and there was not a clear difference for seed dormancy between breeding lines and their parents. We conclude therefore that more work involving the use of new genetic sources or new breeding techniques, will be necessary for breeding advanced lines that maintain a sufficient tolerance to PHS in humid Japanese weather condition.
