Identification and mapping of a quantitative trait locus controlling extreme late bolting in Chinese cabbage (Brassica rapa L. ssp pekinensis syn. campestris L.) using bulked segregant analysis - A QTL controlling extreme late bolting in Chinese cabbage

DNA markers linked to a locus controlling an extreme late bolting trait, wh ich was originally found in a local cultivar of a non-heading leafy vegetab le, 'Osaka Shirona Bansei' (Brassica rapa L. ssp. pekinensis syn. campestri s L.) were identified using bulked segregant analysis. A doubled haploid (D H) line, DH27, which is a progeny of 'Osaka Shirona Bansei', shows extreme late bolting, and bolts without vernalization. DH27 was crossed with a norm al bolting DH line, G309. The plantlets of the parents, F-1 and F-2, were v ernalized and then grown in a greenhouse. The bolting time of F-2 plants sh owed a continuous distribution from 19 to 231 days after vernalization (DAV ), suggesting the effects of a few major genes and polygenes. Possible link age markers for this trait were screened by modified bulked segregant analy sis (BSA). The BSA using four bulks suggested that a 530-bp RAPD band RA125 5C was linked to a locus controlling the bolting trait. The RAPD band was c loned and used as a probe to detect RFLP. The fragment detected a single lo cus, BN007-1, the segregation of which in the F-2 population matched that o f RA1255C. Three other RAPDs were found to be linked to BN007-1. A quantita tive trait locus (QTL) affecting the bolting time was detected around BN007 -1 using MAPMAKER/QTL. Since the difference between bolting times of both t he parental genotypes in the F-2 was 138 days, these markers may be useful for a marker-assisted selection (MAS) in the breeding program for late bolt ing or bolting-resistant cultivars in B. rapa crops.