[ Objective ] This study aimed to analyze the inheritance of bolting associated traits in Brassica rapa, which will provide useful information in a breeding program for late-bolting or bolting-resistant cultivars of Chinese cabbage. [ Method] Three phenotypic measurements, bolting index, flowering time, days to 5 cm elongated stalk, respectively were used for inheritance analysis of six generations, P, （bolting resistant inbreed line ）, P2 （vernalization independent type） and their filial generations F1 , B1, B2 and F2, using the mixed major-gene plus polygene inheritance model. [ Result] The two traits, bolting index and days to 5 cm elongated stalk, both were controlled by two major genes with additive-dominant-epistatic effects （ B-1 model） in hybrid. The flowering time was controlled by one major gene with addltive-dominant effects plus additive-dominant-epistatic effects （D model）. The heritability of the major genes in B1, B2 and F2 were 96.22%, 93.33%, 93.55% for bolting index, 70.68%, 70.68%, 70.64% for flowering time, 79.44%, 79.55%, 79.38% for days to 5-cm elongated stalk, respectively, but no polygene heritability was detected in BI, B2 and F2 generation. It indicated that the bolting trait in Brassica rapa was controlled by one or tow major genes. [ Conclusion] This implied that in the genetic improvement for bolting resistant trait major gene was a main factor. It is fit for early selection and environment factor should be mentioned.
An F2 population, derived from a cross between the vernalization independent genotype ＇ RcBr＇ and the vernalization dependent genotype＇08A061 ＇ , was developed to eonstruet a linkage map with 165 SSR and InDel markers. QTL analysis was performed by two phenotypie evaluation （ days to 5 em elongate stalk and flowering time） based on the difference in F2：3 families under vernalization and no vernalization. The results showed that the vernalization requirement was reeessive in Brassica rapa. Seven QTLs that controlled vernalization requirement were detected on A02 and A06 linkage groups, which explained phenotypic variation ranging from 0.08% to 22.52%. Two QTLs （ VR-DE01, VR-b391 ） were detected on the top of A02, which explained 22.52% and 14. 54% of the phenotypic variation, respectively, and closely linked with BrFLC2 gene. Two QTLs （VR-DE03, VR-DE04） were deteeted on A06 with 13.30% and 13.64% of phenotypie variation. These detected QTLs will provide useful information on understanding the genetic basis between vernalization requirement and bolting, and that will be useful for marker-assisted selection （MAS） in a breeding program for bolting resistant eultivars.
