Raising and characteristics of 'Chinese cabbage parental line 8' (Brassica rapa L. ssp. pekinensis) with a trait of extra late bolting

'Chinese cabbage Parental Line 8' (Brassica rapa L. ssp. pekinensis) with a trait of extra late bolting was bred from a cross between typical Japanese Chinese cabbage and 'Leafy Green Parental Line 2' with long-day requiring late bolting material. After crossing, selection of late bolting and back-crossing with typical Japanese Chinese cabbage were conducted three times to develop Chinese cabbage with a trait of extra late bolting. Based on the tests of specific characteristics conducted in Aomori and Aichi Prefectures for three years, this line was registered as 'Chinese cabbage Parental Line 8', synonym of 'Hakusai Chuukanbohon Nou 8' in 2005. Degree of late bolting of 'Chinese cabbage Parental Line 8' is superior to some leading commercial cultivars with late bolting. In addition, this line shows higher bolting resistance comparing with 'Chinese cabbage Parental Line 6' having low sensitivity to low temperature that was previously registered in our laboratory. However, some heading characteristics of 'Chinese cabbage Parental Line 8' are inferior to commercial late bolting Chinese cabbage cultivars. Days to bolting after seeding of F1 hybrids between 'Chinese cabbage Parental Line 8' and non-bolting-resistant cultivar 'Muso' were intermediate compared to parents. Furthermore, the F2 generations were the same as the F1 and also showed segregation with near non-bolting-resistant types and also extra late bolting types. From these results, it seems that this extra late bolting may be controlled by a small number of genes with major effect. 'Chinese cabbage Parental Line 8' can be easily used for bolting-resistant Chinese cabbage breeding, because more than 10% of the extra bolting resistant individuals were observed in the F2 segregated population.