Molecular Marker-assisted Selection In Hybrid Generation In Cabbage (Brassica Oleracea Var. Capitata)

Cabbage (Brassica oleracea var.capitata), which native to the Mediterranean region with the characters of great resistance and adaptability, has been cultivated all around the world and in China as an importan vegetable crop after being introduced in the 16th century. Accroding to current vegetable breeding goals in China, it is a mission to cultivate disease resistance, high quality and high productivity new lines to vegetable breeders. Therefore, nurturing a number of pyramiding varieties of cabbage which combining high quality and disease resistance is the most pressing matter of the moment. Identification of the phenotype of traditional methods is difficult to accuretely select two or more excellent genes in one individual. Application of molecular markers can solve this problem, then rapid and accurate selection of individuals containing several targent genes can be achieved. Marker assisted selection was used in this research for screening individuals possessing disease resistance genes and later bolting gene in traditional cross and backcross progenies, which was aimed to provide a basis for gene pyramiding breeding and to obtain excellent cabbage germplasm.This experiment was mainly composed of two parts:(1) A trail group and two selecting populations were constructed with materials A21 (with high resistance to TuMV and black rot) and P02 (with later bolting gene). BC1F1 population derived from F1 and P02 backcross was used to verify the linkage relation between RAPD marker N1 and later bolting gene with reference to bolting trait in the field. And then converted RAPD marker into SCAR marker.(2) Markers linked to later bolting gene, black rot resistance gene and TuMV resistance gene were analyzed and used to selecte cultivars possessing multiple gene of interes, which provided a basis for marker assisted breeding in headed cabbage.The main results are summarized as follows:(1) The linkage relation between N1 marker and later bolting gene was verified accroding to the result that the identification of phenotype in the field is identicial to those of N1 marker.(2) RAPD specific fragment was recovered, cloned and sequenced, and a pair of SCAR markers was designed based on the obtained sequence. An stable SCAR marker system was established after the optimization of SCAR-PCR reaction. SCAR amplification result were fully identicial with that by RAPD marker in 166 BC1F1 individuals, which demonstrated the accuracy of SCAR marker.(3) Based on the hybridzation, it has become available to choose target genes plants using MAS combined with inoculation and odservation in early generation. Using the SCAR markers linked to later bolting gene and TuMV resistance gene previously recovered and the SSR marker linked to black rot resistance gene identified,38 pyramiding individuals containing later bolting gene, black rot resistance gene and TuMV resistance gene,132 pyramiding individuals containing later bolting gene and black rot resiatance gene, and 60 pyramiding individuals containing later bolting gene and TuMV resistance gene were selected from the progenies of BC1F2 and F3. And the pyramiding plants can be used as excellent germplasm in cabbage quality and disease resistance breeding.(4) The system of later bolting, black rot resistance and TuMV resistance marker assisted breeding has been established preliminarily. The result showed that MAS pyramiding breeding can not only increase the accuricy and efficiency of progeny selection but also save time required during breeding cycles to a large extent.