Genetic Analysis And Mapping Of QTL Related To Head-splitting Resistance Traits In Cabbage(Brassica Oleracea Var.capitata)

Cabbage （Brassica oleracea var. capitata） is a major vegetable crop which widely cultivated in ourcountry, playing a significant role in all-year supply of vegetables as well as in earning foreignexchanges through exports. However, there is a phenomenon that it is easy to crack for the head ofcabbage during the later stage of growth. It would not only affect the quality of appearance and yield,but also affect its merchantability and storability seriously and cause tremendous effect and economicloss on the production of cabbage. Now the way to select the trait is using the general breeding means,which is not in high efficiency. Researching the inheritance of this trait deeply and building a highdensity molecular genetic linkage map and mapping QTL controlling the trait of resistance tohead-splitting will speed up the breeding process to cultivate new varieties and improve breedingefficiency greatly.The two kinds of mixed major gene plus polygene inheritance models were used to analyze theinheritance of the trait of resistance to head-splitting in the Brassica oleracea var. capitata based on DHpopulation and six generation materials; constructed the molecular genetic linkage map with SSRmarkers using the DH population which is used to map QTL controlling the trait of resistance tohead-splitting so as to get more complete genetic information, which will provide a theoretical basis andguidance for the cabbage breeding of new materials and cultivars of resistance to head-splitting.Themain results were as follows:（1） A double-haploid （DH） population including157lines was obtained by microspore culturefrom the F₁derived from the cross of two advanced inbred lines ‘79156’（splitting-susceptiblity） and‘96100’（splitting-resistance） of cabbage existing significant differences between the resistance tohead-splitting and main agronomic characters.（2） The two kinds of mixed major gene plus polygene inheritance models were used to analyze theinheritance of the trait of resistance to head-splitting in the Brassica oleracea var. capitata based on DHpopulation and six generations （P₁、P₂、F₁、B₁、B₂and F₂）. It was showed that the trait was controlledby two additive-dominant-epitasis major genes plus additive-dominant-epitasis polygenes （E-0model）in the joint analysis of the six generations, the additive effect for the two major genes was foremost andthere was some interaction between the two major genes. In2010, the major genes,heritability of B₁, B₂and F₂were estimated to be67.3%,1.4%and59.1%, the heritability of polygenes were0,56.2%and0.The average environmental variance and the genetic variance accounted for39.1%and60.9%of thephenotypic variance. In2011, the major genes,heritability of B₁, B₂and F₂were estimated to be85.5%,22.3%and84%, the heritability of polygenes were0,24.3%and0, the average environmental varianceand the genetic variance accounted for39.1%and60.9%of the phenotypic variance. The resultindicated that the trait was controlled by three additive-epistasis major genes plus additive-epistasispolygenes （G-0model） through the study of doubled haploid （DH） population. The heritability of majorgene was76.8%while the polygene was10.77%. It indicated from above that the trait of resistance to head-splitting in cabbage was dominated by major genes and the environmental factors have a greateffect on it, in addition, higher hereditability of major genes can be favorable to an efficient selection inearly generation of F₂and B₁for cabbage breeding of resistance to head-splitting.（3） The software Joinmap4.0was used for linkage analysis. As a result, it got a linkage geneticmap which contained nine linkage groups,135SSR markers. The linkage genetic map covered906.7cM with an average interval of6.7cM. The number of markers in every linkage group varied from3to24, which covered the genetic length from32.0cM to189.5cM, average interval distance from3.3cMto10.74cM. The SSR markers in eight linkage groups were not evenly covered which showed a gapabove10cM, in which the largest one was34.8cM. Also, there were some concentrated regions,especially in LG9.（4） MapQTL4.0software and IM&MQM mapping methods were applied in studying thequantitative trait loci （QTL） controlling the trait of resistance to head-splitting in cabbage. Four QTLsrelated the trait of resistance to head-splitting were mapped, located in the LG4, LG5, LG9. The LODvalue were3.38、3.08、4.03and4.3, which explained the variance of trait9.1％、9.1％、9.7％and10.5％,explaining the genetic variation of38.4%. The additive effects were10.84、9.20、-9.80and-10.81.