Genetic Dissection Of Resistance To Turnip Mosaic Virus And Black Rot In Radish (Raphanus Sativus L.)

Radish (Raphanus sativus L.) is a kind of cruciferous vegetable crops, and it has a very long history of cultivation and has occupied an important position in the vegetable production of China. Disease in radish has been always an important factor affecting the production of radish in China, and the most prevalent and serious diseases are turnip mosaic virus (TuMV) and black rot. In order to achieve effective prevention and treatment of the diseases and improve the quality and yield of radish, the most fundamental solution is to develop resistant varieties. China is one of the origins of radish and it is rich in radish genetic resources, so it has great significance to evaluate the resistance of the rich germplasm resources to TuMV and black rot, discover elite resistant genetic resources, further clarify its resistance inheritance and mine resistant genes for disease-resistance theory study and radish breeding practice.Based on above background and purpose, a repeated identification was carried out on the resistance of representative radish germplasm to TuMV and black rot, which were preliminarily identified in the previous study in our lab.Based on the typical resistant and susceptible radish germplasm screened out, the resistance inheritance of the given resistant genetic resources to TuMV and black rot were studied at the phenotype, and their resistant inheritance were further analyzed at molecular level by constructing radish molecular genetic map, locating QTLs and developing molecular markers. The main conclusions of this paper are as follows:1. Repetitive identification on the resistance of representative radish gerplasm to TuMV and black rot: The twenty-six inbred lines with obvious difference in the resistance to TuMV and black rot were repeatedly indentified in the light of previous preliminary identification in field conditions and at seedling stage.The result showed that 12 inbred lines were high resistant to TuMV , 8 inbred lines resistant, 5 inbred lines moderate resistant and 1 inbred lines susceptible; and 3 inbred lines were resistant to black rot , 6 inbred lines moderate resistant , 6 inbred lines susceptible, 11 inbred lines high susceptible. From the results, we found 2 inbred lines were resistant both to TuMV and black rot, and 1 sample was susceptible both to TuMV and black rot among them.2. Genetic analysis on the resistance of the given resistant germplasm to TuMV and black rot at the phenotype level: The resistance inheritance of radish germplasm to TuMV and black rot were studied through the combining ability analysis of complete diallel cross. It was made definite that the resistances to both diseases were dominant or partly dominant to susceptibility. The principle of parent choice and matching on the basis of the S.C.A and G.C.A was stressed in cross breeding of disease-resistance. The resistance inheritance of typcal resistant resources to TuMV and black rot was further analyzed using the joint segregation analysis of a mixed genetic model of major gene plus polygene in generations. It was proved that the inheritance of radish resistance to TuMV obeyed the"two pairs of additive - dominance– epistasis major gene plus additive - dominance– epistasis polygenes"genetic model; and the resistance inheritance of radish to black rot disease obeyed the"a pair of additive - dominance major gene"genetic model, and the polygenes effect existed at the same time. and the major gene heritability(MGH), the polygene heritability(PGH) and the ratio of environmental variance (EV) to total variance (TV) were estimated on the base of the genetic models. The MGH and the PGH for the resistance to TuMV were respectively 55 %⁹5 % and 0⁴0.9 % , the ratio of EV to TV was 4.3 %¹0.1 % in different segregation populations; MGH and PGH for the resistance to black rot were 72.4% and 9.07%, the ratio of EV to TV was 18.5% in F2 population.3. Construction of radish molecular linkage map: A F2 segregation population was established applying two radish inbred lines which were obviously different in the resistance both to TuMV and black rot. A molecular genetic linkage map of radish was constructed on the basis of the population by two optimized molecular marker methods of SRAP and SSR. The molecular genetic linkage map included nine linkage groups and 196 markers, its total length was 736.2 cM, with an average map distance of 3.76 cM.4. QTL Mapping and molecular tagging of resistant genes to TuMV and black rot: The QTLs and their genetic effects of the genes resistant to TuMV and Black rot were mapped and dissected on the basis of the radish molecular genetic linkage map and with the multi-QTL model. It was found that 4 target QTLs intensively locating in LG3 and LG5 linkage groups. Among them 2 QTLs were related to the resistance to TuMV, of which one was effect-enhancing with the contribution rate of 7.3 %, another was the negative-effect with the contribution rate of 11.7 %. And 2 QTLs were related to the resistance to black rot, of which one was effect-enhancing QTLs and one was the effect-reducing QTL,the contribution rate was 26.6 % and 45.3 %.Meanwhile, the resistance gene to TuMV was tagged with help of the bulk segregation analysis (BSA). It was found that a molecular marker CoMe7F/BEm12R-120 was linked to resistance gene with the genetic linkage distance is 7.9 cM.5. Molecular tagging of resistant genes corresponding to avirulence genes of black rot pathogen in radish:Twenty radish inbred lines with obvious difference in resistance to black rot were screened with 8 strains containing different avirulence genes that were isolated from black rot pathogen Xcc₈004. It was demonstrated that 12 lines of them appeared resistant response to different avirulence gene strains, suggesting the existence of corresponding resistant genes. The molecular marker for the resistant gene corresponding to avirulence gene Xcc₃176 was studied in a segregation population F2 constructed from KB07-3 and KB07-10. By using of the BSA method and SRAP molecular marker system, a molecular marker CuMe6F/CoEm11R-260 was obtained, which was closely linked to the resistant gene with a genetic linkage distance of 7.6 cM.