Molecular Marker Analysis And Mapping Of Clubroot Resistance Gene In Chinese Cabbage

Chinese cabbage (brassica rapa l.ssp.pekinensis) has been widely planted inchina owing to its nutritional value and various ecological types. Clubroot is aworldwide soil-borne disease which is caused by the obligate biotroph protistPlasmodiophora brassicae Woronm. It’s one of the most serious diseases in Brassicaspecies all over the world. Chinese cabbage is more vulnerable to clubroot comparedwith short-term crops such as Pak Choi，Mizuna， or Mibuna， which are moresusceptible. Clubroot happened in many countries in the world for a long time andspread quickly. Chinese have large area to cultivate the Chinese cabbage， so thedegree of harm is stranger than other countries. Thus clubroot has become one of themost urgent diseases in China.Therefore breeding Chinese cabbage clubroot resistant varieties are the mosturgent problem currently. Developing molecular markers that tightly linked withclubroot resistant gene plays a vital role in the processing of breeding resistantvarieties.Xin ye cheng jiao town in Xinye country is the most serious region in Henanprovince. We select this area as a field inoculation tests. In order to ensure theaccuracy and repeatability of experiments， before to be planted， we should ensureP. brassicae distributed evenly. Artificial inoculation tests were constructed in HenanAgricultural Science Horticultural Research Institute.bacteria source is also comefrom cheng jiao town.Both field and artificial inoculation tests were conducted to evaluate theresistance of six F2populations. Based on BSA (Bulk Segregant Analysis) methodand molecular marker techniques， several linked markers were obtained andclubroot resistance genes were preliminary mapped. The results are as follows:1. Six F2populations were generated by self-pollination of6different F1resistanthybrids. Field tests were conducted on4populations while artificial tests wereconducted on the other two populations. All of the six populations showed phenotypicsegregation and the segregation ratios fitted to the3(resistant):1(susceptible) ratio. It suggested that the character of clubroot resistance in these materials might becontrolled by a single dominant gene,respectively.2. We used BSA method to screen molecular markers in populationY635F2,Y636F2,Y637F2,Y642F2,Y664F2and Y665F2，to obtain markers linked toclubroot resistance genes. In population Y635F2， we find four SSR markers whichis GC1160，GC2360-2，GC2920-2F and SASS70linked to the clubroot resistancegene. In population Y636F2， we find four SSR markers which is GC1160，GC2360-2，GC2920-2F and SASS70linked to the clubroot resistance gene. Inpopulation Y637F2，we find four SSR markers which is GC3070，GC2920-2F，SASS70andBGA06linked to the clubroot resistance gene. All above markers werelocated in chromosome A03. In population Y642F2，there have five Indel markerBrID10781、BrID11233、BrID10867、BSA2、BSA7and two SSR markers A08-S17and A08-S33were identified linked with CR gene. In population Y664F2，there havefour Indel marker BrID10781、BrID11233、BrID10867、BrID110265and two SSRmarkers A08-S17and A08-S33were identified linked with resistance gene. Two ofthe population CR gene were mapped in chromosome A08. In population Y665F2，we found none molecular marker linked with CR gene.3. In F2population Y642F2and Y664F2， the CR genes were both mapped inchromosome A8of Brassica.rapa. Among seven markers we found in F2populationY642F2， BSA2is nearest to CR gene which genetic distance is16.9cM.The farthestmarker is BrID10781and genetic distance is48.0cM. For the F2population Y664F2，A08-S17is nearest to CR gene which genetic distance is47.0cM， BrID10265isfarthest to CR gene which genetic distance is66.3cM.In this research we used six F2population to conduct resistance identification.We obtained several makers which are tightly linked to CR gene. All we did couldaccelerated the processing in Chinese cabbage breeding of clubroot-resistant.Meanwhile， the results also lay the foundation for fine mapping and clone ofclubroot resistance genes.