Abstract
Aphanomyces root rot is a serious disease of sugar beet (Beta vulgaris L.) in poorly drained fields. This study was conducted to clarify the influence of cultivation methods on the disease intensity using a resistance cultivar cultivated by direct sowing or by transplanting in the Aphanomyces-infested field. As a result, there was no significant relationship between cultivation method and disease severity in 2018, because the root expansion was severely suppressed due to the high moisture condition. However, in 2019, the damage caused by disease in the plants cultivated by direct sowing was more severe than that in the plants cultivated by transplanting. In addition, root weight was significantly reduced in the plants cultivated by direct sowing compared to those cultivated by transplanting in both years. Hence it was suggested that the economical damage of Aphanomyces root rot was a more serious problem under direct sowing. On the other hand, the disease intensity of cultivars observed no significant differences under the two cultivation methods, the resistant cultivars “Hokkai_Mitsuboshi” and “Kachihomare” showed significantly superior disease indices and yield than the less resistant cultivars. These findings suggested that the damage caused by Aphanomyces root rot is serious in plants cultivated by direct sowing, and that utilization of a resistant cultivar would be an effective for its control.
