Abstract
Wheat yellow mosaic is a soil-borne virus disease, and has spread in recent years. The disease incidence is known to decrease by delaying the seeding time, and a high air temperature and a lot of rain after seeding result in serious damage in the spring. Thus, the effect of winter-seeding cultivation (W.S.) seeding before continuous snow cover, on the disease incidence of wheat yellow mosaic was investigated using susceptible winter wheat (cv. Nanbukomugi). In the field infested with wheat yellow mosaic virus (WYMV), the disease degree was compared in wheat plants cultivated by two cultivation methods [standard autumn-seeding cultivation (S.A.S.) seeding from early October to mid-October and W.S. (seeding from early December to mid-December)]. In S.A.S., the disease incidence and the disease severity were 100% and 99 in the field highly infestated with WYMV. In W.S., the disease incidence and the disease severity were 0—5% and 0—2, respectively, which were significantly lower than those in S.A.S.. The mean air temperature after seeding in S.A.S. was high, and the number of days with mean air temperature above 5°C which is thought to be suitable for infection of wheat with WYMV was 40 or more. On the other hand, the mean air temperature was below 5°C from seeding date to late March after snow melting in W.S.. We consider that the incidence of wheat yellow mosaic in W.S. was suppressed by low temperature after seeding. In W.S., the ear number was larger, the thousand grain weight was heavier, and the grain yield was 23—65% higher than those in S.A.S..
