QTL Mapping Of Resistance Gene To Downy Mildew And Powdery Mildew In Cucumber

In this study, a population of F2 derived from cucumber line K8 ( high resistance to downy mildew and powdery mildew) and line K18 ( high susceptible to downy mildew and powdery mildew) was used to analysis the resistance gene to downy mildew and powdery mildew, and to construct the molecular genetic map. F2:3 families were evaluated for resistance analysis. 2360 pairs SSR primers were used to construct the genetic map, and QTL mapping of resistance gene to downy mildew and powdery mildew were performed with composite interval mapping. The main results are summarized as the followings:(1) The identification experiments were carried out using the leaf spray inoculation in greenhouse. The identification results of downy mildew and powdery mildew show that: parents K8 was resistant; parents K18 was susceptible; F1 was susceptible. The resistance of K8 parent to downy mildew and powdery mildew was both controlled by recessive gene. The disease index showed the continuum characteristics in the F2 population, the results fitted the normal distribution, and genetic parameters were also consistent with the characteristics of Quantitative Traits. The results suggested that the genetic of resistance to downy mildew and powdery mildew were controlled by multiple genes. And the same results were got by analyzing of disease index data of 2004 spring.(2) In this study, 2360 pairs of SSR primers were used to screen the polymorphism of parents and resistant-susceptible pools. Total 53 pair primers were selected and used for analysis of the F2 population. 42 SSR markers could be used to construct linkage map. Then, cucumber genetic map which had 8 linkage groups and covered 287.4cM, was constructed by 39 SSR molecular markers. The average distance of markers was 7.37cM. 2~11 markers were found in every linkage group.(3) QTL analysis of resistance gene to downy mildew in cucumber. In 2004 spring experiment, two resistant QTLs (dm1.1, dm3.1) were detected by interval mapping (CIM) method and located on the chromosome 1 and chromosome 5, and they explained 18.6% and 19.5% of the phenotypic variation, respectively. In 2009 spring experiment, two resistant QTLs (dm2.1, dm3.2) were detected and located on the chromosome 6 and chromosome 5, and they explained 7.6% and 10.7% of the phenotypic variation, respectively. In 2009 autumn experiment, one resistant QTL (dm3.3) was detected and located on the chromosome 5, and it explained 19.6% of the phenotypic variation.(4) QTL analysis of resistance gene to powdery mildew in cucumber. In 2004 spring experiment, three resistant QTLs (pm3.1,pm3.2,pm3.3) were detected by interval mapping (CIM) method and located on the linkage group3 (chromosome 5), and they explained 36.1%, 16.7% and 7.3% of the phenotypic variation, respectively. In 2009 spring experiment, four resistant QTLs were detected. One QTL(pm2.1)located on the chromosome 6, and it explained 5.2% of the phenotypic variation. The other three QTLs(pm3.1,pm3.2,pm3.3)located on the chromosome 5 and were same the location with QTLs in 2004 spring experiment. These three QTLs were considered same QTLs in different experiments, and named same code name. And they explained 41.6%, 9.8% and 6.4% of the phenotypic variation, respectively.For resistance gene to downy mildew, 5 QTLs were detected. Totally, two resistant QTLs in 2004 spring experiment, two resistant QTLs in 2009 spring experiment and one resistant QTL in 2009 autumn experiment explained 38.1%, 18.3% and 19.6% of the phenotypic variation, respectively. For resistance gene to powdery mildew, 7 QTLs were detected. Totally, three resistant QTLs in 2004 spring experiment, four resistant QTLs in 2009 spring experiment explained 60.1% and 63% of the phenotypic variation, respectively.