Breeding materials for resistance to Verticillium wilt in Japanese cabbage (Brassica oleracea L. var. capitata)

Japanese cultivars of cabbage (Brassica oleracea L. var. capitata) were screened for their resistance to Verticillium wilt caused by Verticillium longisporum syn. V. dahliae Klebahn. No immune cultivar was found in a screening test of 51 Fl hybrids in a severely infected field, but some progenies of Kandama type (summer sowing type) such as 'Shutoku','YR Ranpo','YR Bibo', 'Kusabue 2', and Harukei type (fall sowing type) such as 'Kinkei 201' and 'YR 506' showed little or no symptoms. Thus, they possess enough resistance for commercial usage. Most Kandama type with resistance originated from crossing with the old Japanese cv. Kawasaki or Aichinatsumaki, some of the Harukei type with resistance originated from open-pollinated cultivars within the Nakanowase group. The susceptible cultivars of F-1 hybrids which are derived from the Nakanowase and Copenhagen Market groups such as 'Natsuyama', 'Early Ball', 'Teruyoshi' and 'Reiho 1' characteristically masked the diseased symptoms on the leaf. When we inoculated 41 open-pollinated cultivars, some resistant cultivars were discovered in the Aichinatsumaki and Nakanowase groups. These results indicate that cultivars within Aichinatsumaki and Nakanowase groups possess resistance genes to this disease. By raising these progenies from these crosses, we have succeeded in isolating Verticillium wilt-resistant cabbages. Our data reveals that the resistance is controlled by dominant inheritance with some genes.