Genetic Analysis And QTL Fine Mapping Of The Resistance To Black Rot In Radish (Raphanus Sativus L.) Germplasm

Black rot in brassicaceae plants caused by Xanthamonas campestris pv. campestris （Xcc）, which isa bacterial vascular disease occurred all over the world. This disease affects most of cruciferousvegetables, including radish, turnip, cabbage, cauliflower, Chinese cabbage, etc. China is the biggestradish producer in the world. Black rot can happen from radish seedling stage to harvest time anddamage all parts of radish. At present, it is thought that disease-resistant breeding is the most idealmeasure in prevention of black rot. Therefore, it is very important of digging resistance genes andbreeding disease-resistant varieties.In this study, two rare radish germplasms （inbred lines） resistant to black rot were used for F2population development, and the genetic characteristics of their resistance to black rot were studied.Meanwhile, one of inbred line resistant to black rot and one susceptible inbred line were used toconstruct F2populations. A genetic linkage map was constructed and QTL of resistance to black rotwere identified based on the F2populations.1. Two radish inbred lines resistant to black rot （KB10Q-22, KB10Q-24） and one susceptibleinbred line （KB10Q-33） were used to construct F2populations. Black rot pathogen Xcc8004were usedto inoculate seedlings by leaf-cutting+spray method to identify the disease-resistance of all plants. Thegenetic characteristics of resistance to the black rot were studied with a mixed model of major genesplus poly-gene using P1, P2, F1, F2populations. The results showed that the inheritance of theresistance of the above two resistant lines to black rot was different. The plants of F1generation fromKB10Q-22expressed resistant. Its genetic model was mixed two major genes withadditive-dominance-epistatic effects plus poly genes with additive-dominance-epistatic effects （E₀model）, while the plants of F1generation from KB10Q-24expressed susceptible, and its genetic modelwas mixed one major gene with additive-dominance effects plus poly genes withadditive-dominance-epistatic effects （D₀model）. Major gene heritability for the two crosses was87.73%and55.64%, respectively. The heritability was mainly dominated by major genes.2. A genetic linkage map was constructed with F2population of120plants from the cross of oneinbred line resistant to black rot “KB10Q-22” and one susceptible inbred line “PP10Q-36” usingRAD-Seq technology. The map was consisted of9linkage groups, including3393SNPs, its total lengthwas3621.6cM, with an average map distance of1.55cM. Black rot pathogen Xcc8004was used toinoculate the seedlings to120F3populations by leaf-cutting method to identify the disease-resistance.Based on the genetic linkage map,14QTLs of the resistance to black rot were mapped with the methodof inclusive composite interval mapping （ICIM）. There were4QTLs （qBRR-9-1, qBRR-6-1, qBRR-6-2,qBRR-6-3）, which LOD values were greater than4.0. qBRR-9-1was located in LG9, the contributionwas47.28%. qBRR-6-1, qBRR-6-2and qBRR-6-3were all located in LG6, the contribution were14.65%,14.96%and14.41%, respectively.3. The radish inbred line resistant to black rot “KB10Q-22” and one susceptible inbred line “KB10Q-33” were used to construct F2populations. Black rot pathogen Xcc8004was used to inoculatethe seedlings by leaf-cutting+spray method to identify the disease-resistance. According to the resultsof QTL analysis and radish genome sequence, we designed102pairs of SSR primers near the initiallocus.11pairs of primers linked with black rot resistant genes were screened with BSA method. Using11pairs of SSR markers amplified the DNA of the extreme recessive plants of F2populations, theresistant gene were mapped between QTL1-21and M26. Then, a genetic map was constructed with F2populations using4pairs of primers linked with black rot resistant genes. Based on the map and theresistance datas, QTL of the resistance to black rot were also mapped between QTL1-21and M26. Thegenetic distance of the two markers was0.5cM and the physical distance was59Kb. There was aresistant signal gene RAR1in this interval.