QTL Mapping Of Clubroot Resistance,Bolting And Flowering Traits Based On High Density Genetic MAP Of Radish (Raphanus Sativus L.)

Raphanus sativus L.is the important cruciferous vegetable crop,with great cultivated area and output next to Chinese cabbage in China,and plays an important role in Chinese diet.Due to the occurrence of clubroot disease,there were serious loss in the yield and quality of radish and brassica crops,including Brassica rapa,Brassica oleraceaand Brassica napus.Additional,earlier bolting can bring about empty holes inradish fleshy roots,resulting in reduction in commodity quality of radish.Studies on the mechanisms related to radish resistance to clubroot and early bolting are of great significance to the selection and breeding of excellent radish cultivars.In this dissertation,we localized the genes of radish involved in resistance to clubroot and flowering traits,developed the molecular markers of radish resistance to clubroot,and explored the candidate genes regulating flowering.The main results are listed below: 1.Construction of high-density genetic map of radishA high-density genetic linkage map was constructed using rad-seq technology.The genetic map contained a total of 1,148 genetic markers,covering a total length of 794.3c M in the radish genome,with the average genetic distance of 0.7 c M between the markers The linkage group R01 was the longest,covering a distance of 139.7c M with an average of 0.9c M.The linkage group R03 was the shortest,covering a distance of 26.4c M with an average distance of 0.3c M.R05 possesses the maximum number of markers?200?,and the minimum number of tags occurs in R07?66?.Markersin the whole map were more evenly distributed than those in the previous ddrad-seq map,the genetic map had a higher resolution than the genetic map obtained by other simplified genome sequencing methods.2.QTL mapping and molecular marker development for radish clubroot resistanceFive QTLS?Rs Cr1,Rs Cr2,Rs Cr3,Rs Cr4,and Rs Cr5?related to radish clubroot resistance were preliminarily identified in F2 and F2:3 families.7.26%³1.38% of phenotypic variationswere explained by these QTLs.Rs Cr4 and Rs Cr5 were located on chromosome 8 and 9 of radish,respectively.Collinear analysis showed that Rs Cr4 might be homologous to Crr1.38 disease-resistant genes were excavated in the localization interval,and 20 pairs of SSR primers were developed according to the marker sequences of the disease-resistant genes in the interval,and 5 pairs of polymorphic markers were screened out to obtain a SSR marker fold92946₄806 that can be used for molecular marker-assisted breeding.3.QTL mapping and candidate gene mining for flowering traits in radishAccording to the results of QTL localization,we detected two QTL loci related to radish flower bolting.By comparison with radish reference genome,a total of 618 genes were found in the main effect zone of the QTL,including Rsa10025740 candidate gene showing significantly high express during bolting and flowering,suggesting the candidate gene might play aimportant role during boling and flowering.To sum up,the QTLs identified in this dissertation provides valuable information for further exploring disease resistance genes and understanding the molecular genetic mechanism of resistance to radish clubroot,and the developed molecular markers can also provide effective technical support for the breeding of radish withresistance to clubroot.Accoring to of QTL mapping of radish bolting flowering traits,two QTL loci related to radish bolting flowering radish were detected,and a candidate gene Rsa10025740 was found to have significantly high express in parent lines during bolting and flowering,suggesting the candidate gene might play an important role during radish bolting and flowering.However,the detailed functions of the candidate gene during the radish bolting and flowering should be further investigated in order to provide theoretical basis for further development of molecular marker-assisted breeding.