Construction Of A Molecular Genetic Map And QTL Mapping For Major Agronomic Traits In Chinese Cabbage(Brassica Campestris Spp.pekinensis)

Chinese cabbage （Brassica campestris L. ssp. pekenensis） is originated from China, which has thelargest cultivation area. Many important agronomic traits of Chinese cabbage are quantitative traits, so it isnecessary to construction a genetic map and map QTL on the linkages. The study tried to opitimize themicrospore culture technique and obtained a DH population. Based on the SSR and SRAP markers, agenetic map was constructed for mapping the important agronomic traits. Marker analysis was performedon192doubled haploid （DH） lines obtained from F1progeny of two homozygous parents. The mainresults of the present study were as follows:1. In order to establish an efficient technique system of isolated microspore culture and constructionimmortal mapping population in Chinese cabbage, isolated microspore culture was performed using13F1hybrids of Chinese cabbage. Genotypic difference in embryogenic response was observed, the highestfrequency of embryogenesis was10.6embryos per bud, and one genotype did not response toembryogenesis. Heat shock treatment is efficient for embryogenesis, compared with the longer incubationperiod （72h）, heat shock treatment at33℃for24or48h was more beneficial for microsporeembryogenesis. The embryogenesis frequency can improve2-3fold by adding ‘0.1mg·L^-16-BA+0.05mg·L^-1NAA’to NLN-13medium. While anti-auxin PCIB is used to enhance microspore embryogenesisand plant regeneration without an intervening callus phase. The optimum concentration of PCIBapplication was found to be40μM in NLN-13medium, which resulted in a3.4-to6.2-fold increase in thenumber of embryos （8.27-19.2embryos per bud） and a9.6-fold increase （21.33%） in the plant regenerationfrequency in comparison with the controls. The embryos, produced in NLN medium supplemented with40μM PCIB and transferred at the21-day-old reached the high direct plant regeneration rate. The highestplant regeneration rate reached to67.4%and the average spontaneous doubling frequency of the differentgenotypes of B. rapa was57.5%.2. A genetic linkage map of Chinese cabbage was constructed, which was based on a DH populationwith192inividuals. SSR and SRAP were adoptd and233markers including43SSR,190SRAP markerswere integrated into the resulted map using Joinmap3.0version. This map consisted of10linages groups,covering1063.8cM with a mean marker intervalof4.6cM, the largest interval between markers was18.0cM. Various linkage groups were feature by14-32markers,38.2-150.5cM length. The10linkagemaps can correspond to chromosomes by the anchor SSR markers. Among the233polymorphic markers,149（63.9%） deviated from the Mendelian segregation ratios.3. Based on a linkage map with233markers, QTL network2.0is used to investigate QTL of themajor traits related to plant morphology using the data collected under two locations.37QTLs and4paisrof epistatic loci controlling8agronomic traits related to morphology traits were mapped on9linkages.These QTLs included4for plant heitht,3for plant diameter,7for leaf length,6for leaf width,4for leaflength/Leaf width,2for petiole length,5for petiole width,6for petiole thickness. The explained varianceswere different, ranged from5.09%-31.37%.24QTL can explain more than10.00%. The QTL controllingleaf width was mapped on A10. The QTL of assoeiated traits often located on the same loci or near regionof a linkage group.2QTLs controlling plant height and leaf length were mapped on the same positon ofA08（73.9cM）,2QTLs controlling leaf length and petiole length were mapped on the same positon of A05（33.4cM）,2QTLs controlling leaf length and petiole were mapped on the same positon of A10（0.0cM）,2QTLs controlling leaf width and petiole thickness were mapped on the same positon of A06（12.7cM）. TheQTLs controlling leaf width and petiole width were detected in the two locations.4. Based on a linkage map with233markers, QTL network2.0is used to investigate QTL of the major traits related to leaf colour traits using the data collected under two locations.51QTLs and7paisr ofepistatic loci controlling colour traits were mapped on7linkages. These QTLs included4for outer leafcolour L,4for outer leaf colour a,4for outer leaf colour b,4for petiole colour1L,4for petiole colour1a,6for petiole colour1b,6for petiole colour2L,4for petiole colour2a,5for petiole colour2b,5for innerleaf colour L,3for inner leaf colour a,3for inner leaf colour b. The explained variances were different,ranged from2.12%⁷3.19%.12QTL can explain more than30.00%.12QTLs controlling petiole colourwere mapped between0.0⁴.0cM on A03, each QTL can explained between34.54%⁷3.19%and manyQTLs were detected in the two locations, this area existed important QTL controlling petiole colour.