Identification Of Molecular Markers Linked To Important Resistant Genes And Construction Of Genetic Map In Cucumber

Cucumber is globally widely cultivated vegetable crop. In China, it is mainly cultivated in the plastic tunnel, providing a year-round vegetable supply. Molecular biological research in cucumber is relative weak, which makes marker-assisted breeding more difficult. However, this also provides us with opportunity to this challenging area. Studies on cucumber molecular breeding will have significant influence on cucumber genetic breeding.Marker assisted selection system and construction of genetic map were two critical technologies in molecular breeding. Disease resistance is one of the most important agricultural traits in the cucumber, but the screening of some disease resistance genes is complicated, often influenced by the environment, pathogens and so on, especially in the identification of some multiple-diseases. Cucumber genetic map construction has made a big progress, but most of the published cucumber genetic maps are constructed based on F₂ populations, and the map density is not saturated, those maps are short of practicable and universal. Based on the molecular tools available and our own expertise, we want to set up a marker-assisted breeding system for five common cucumber diseases through genetic analysis firstly, at the same time, to construct a relative dense genetic map and mapping important traits using RILs, and on the other hand, identify the anchor SSR markers to help integration with other maps to construct maps with even higher density for general and practical uses in molecular breeding.My research has led to the following results:1. Using the RILs and two other F₂ populations, I have carried out genetic analysis on the resistance to five major diseases, Among them, resistances of "Qiupeng" to ZYMV-CH, WMV and PRSV-W were inherited as a single recessive locus, with some minor genes with moderate effects. These three loci were linked together. Resistance of "WIS2757" to fusarium wilt race 4 was inherited as a single dominant allele, its resistance to powdery mildew was controlled by a major recessive gene s, a dominant gene R and a recessive gene I.2. Using these populations, I have identified the molecular markers linked to these five major disease resistance genes, and also established a marker-assisted selection (MAS) system for viruse resistance.1) AFLP markers E-ACG/M-CAG-182 and E-ACG/M-CAG-180, SCAR markers SCAR3-109 and SCAR4-134, RAPD markers AU3-400, R12-1300 and AR1-1500, were linked to the ZYMV-CH resistance gene. The genetic distances were 5cM,10cM,10cM,10cM,1cM,4cM and 6cM, respectively.2) Co-dominant AFLP marker E-ACT/M-CTT-427 and SCAR marker PWMV-214 were linked to WMV resistance gene, and RAPD marker OPQ15-400 was linked to the WMV susceptible gene, with the genetic distances of 2cM, 2cM and 9cM, respectively.3) RAPD marker AP7-1800 was linked to the PRSV-W susceptible gene, with the genetic distances of 3 cM.4) AFLP marker P-GTG/M-CCA-310, SCAR marker SCAR-282 and RAPD marker OPD9-300 were linked to the fusarium wilt race 4 resistance gene, with the genetic distances of 7 cM, 7cM and 14 cM, respectively.5) Two co-dominant SSR markers SSR97-200å’ŒSSR273-300 were linked to the powdery mildew resistance gene, with the genetic distances of 5 cM and 13 cM, respectively. AFLP marker P63M51-384 and SCAR marker PMSCAR-300 were linked to powdery mildew susceptible gene, with the genetic distance of 7cM.6) MAS efficiency of those markers mentioned above were evaluated using BC₁ population, the efficiency of one marker was about 82%-90%, the MAS efficiency of co-used makers was about 95%-100%3. Using the RIL population of a cross between European No. 8 and QiuPeng, a map with 238 markers (139 AFLPs, 4 SSRs, 3 SCARs, 89 RAPDs and 3 morphological traits) was constructed in cucumber. These loci were mapped to 9 linkage groups, spanning a total genetic distance of 727.5 cM, with an average interval of 3.1cM per marker. This was the most saturated genetic map in our China, and it was more universial. This map could be used as the basis map to integration with other maps to construct maps with even higher density for general and practical.4. Three resistance genes to ZYMV-CH, WMV and PRSV-W were mapped into linkage group 2 within 15 cM genetic distances. Mapping of the WMV resistance gene was the first repoted.5. The RIL population and two F₂ segregation populations of cucumber were employed to filter through all the anchoring SSR markers and obtained more than 20 polymorphic markers and 3 markers that could be used for map integration. More markers are needed in the future for a comprehensive integration.