Clubroot of Spring Chinese Cabbage in Nagasaki Prefecture, Kyushu

Since 1988 clubroot of cruciferous vegetables caused by Plasmodiophara brassicae WORONIN has been observed at Shimabara, Nagasaki Prefecture, as an additional incidence in Kyushu. There the clubroot disease damaged severely those vegetables, especially spring Chinese cabbage．Hot-bed nurseries are seeded with the Chinese cabbage during mid November to mid March. Seedlings are grown for about 35 days and transplanted into plastic film houses, film tunnels or outdoor fields. Diseased plants have been found both in these fields and in the hot-bed nursery during the short-day period at which the occurrence of clubroot has been supposed to be suppressed. In the inoculation test, the Shimabara isolate showed high virulence to Chinese cabbage and cabbage even at very low inoculum-density such as 1 × 10^2 spores/g dry soil. The Shimabara isolate, therefore, was presumed to be one of the highest virulent strains. High virulence of the Shimabara isolate may be an important factor, as well as the relatively high indoor temperature in the hot-bed, plastic film house and film tunnel, of the clubroot-incidence during the growth of spring Chinese cabbage under the short-day at Shimabara. The Shimabara isolate was judged to belong to race 4 by WILLIAM'S method, and could not attack all of seven clubroot-resistant cultivars of Chinese cabbage tested. These cultivars may be available to prevent the Shimabara isolate from affecting. Among four fungicides tested for controlling the Shimabara isolate, MTF-651 (under application) was constantly effective. On the other hand, PCNB was hardly effective, and torikuramido and TPN were effective at the low inoculum density such as 1 ×10^4 spores/g dry soil but ineffective at the high inoculum density such as 1 × 10^7 spores/g dry soil.

Plasmodiophora brassicae

Chinese cabbage

clubroot in Kyushu

virulence

environmental condition