Studies On Inheritance Of Clubroot Resistance And Creating Of Clubroot Resistant Material In Brassica Campestris SSP. Chinensis

Non-heading Chinese cabbage (Brassica campestris ssp. chinensis) is one of the most important vegetables worldwide, with abundant nutrients and unique taste. The yield and quality of non-heading Chinese cabbage are severely threatened by abiotic and biotic stresses. Cabbage clubroot (Plasmodiophora brassicae) is one of the most serious diseases in non-heading Chinese cabbage. The disease occurs throughout the growing period of non-heading Chinese cabbage. And seedling stage is particularly devastating. The fungus can cause severe yield reduction in non-heading Chinese cabbage production. Identification and evaluation of resiatance to clubroot is the base for cultivating and applying resistant varieties to prevent clubroot. The clubroot resistance gene from Chinese cabbage were introduced to nonheading Chinese cabbage, the physiological, biochemical of root gall formation, the inheritance and molecular markers of resistance gene to clubroot in non-heading Chinese cabbage(B. campestris ssp. chinensis Makino) were studied by using related populations including P1, P2F1, F2and BC1with seedling inoculation. The objective of this paper was to study the physiological and biochemical mechanisms and to identify molecular marker of resistance to the clubroot.Main results of the study are as follows:1Identification System of Resistance to Clubroot in B. campestris ssp. chinensisTwo methods of Plasmodiophora brassicae inoculation were compared:mixing resting spores of the pathogen with soil and dipping the root of cabbage with P.brassicae suspension. Soil inoculation caused more severe symptoms and the severity of the disease increased with treatment dose.A new set of standards for grading plant disease in the fields is offered based on practical experience.2Development of non-heading Chinese cabbage materials and new variety with clubroot resistance Studies and development of non-heading Chinese cabbage materials with clubroot resistance were carried out for the lack of clubroot resistance variety, In order to selectd clubroot resistant non-heading Chinese cabbage breeding materials, eleven non-heading Chinese cabbage lines(highly susceptible to clubroot)and one Chinese cabbage variety (highly resistant to clubroot)were took as the primary parents to improve the clubroot resistance of non-heading Chinese cabbage lines and provide the materials of the disease-resistant breeding.3Inheritance of clubroot resistance in non-heading Chinese CabbageTo identify whether the resistance of downy mildew converted or not in different growth periods, two parent lines, F1,F2and BC1populations were inoculated in cotyledon and seedling stages using an artificial inoculation method. The results indicated that the F1population (30) all expressed the resistance. In addition, the F2population(73) segregated a clear3:1of resistance to susceptibility,and the BC1population(70) segregated a clear1:1of resistance to susceptibility, which suggested the resistance was controlled by a single dominant locus.4Analyses of ISSR molecular markerThe clubroot resistance gene from Chinese cabbage were introduced to non-heading Chinese cabbage.Inter-simple sequence repeats (ISSR) were employed to detect molecular markers linked to the resistance gene of clubroot in Brassica campestris ssp. chinensis, accompanied with BSA. The results showed that21of the93ISSR primers tested could amplify clear and steady bands, there was3ISSR primers that could amplify polymorphic bands between resistant and susceptible DNA pools composed of10highly resistant plants and highly susceptible plants. Subsequently, the3ISSR markers were verified in single plants, and primer873was found to be significantly associated with the resistance in F2progenies. The genetic distance between the marker and the resistance gene was9.72cM.These results are the basis for molecular marker-assisted selection and identification of disease resistance varieties.