| Downy mildew,a foliar disease caused by the oomycete Pseudoperonospora cubensis,is one of the most destructive pathogens of cucurbits.Resistant cultivars are available but yield losses are high without the use of fungicides.Higher levels of resistance are needed to reduce the use of pesticides while maintaining adequate yields.Thus,Selection and use of resistant varieties are the key methods of control the disease.Screening cultigens for downy mildew resistance and further developing new variety is the most economical and effective way.The populations of F2 derived from cucumber introduction line PI088(high resistance to downy mildew)and variety changchunmici(CCMC,susceptible to downy mildew),F2 populations was used to analysis the resistance gene to downy mildew,and to construct the molecular genetic map.2592 SSR primers(simple sequence repeat,SSR)were used to construct the genetic map,and QTL mapping of resistance gene to downy mildew was performed with composite interval mapping.The main results are summarized as the followings:(l)In this study,2592 pairs of SSR primers were used to screen the polymorphism of parents.Total of 421 pairs primers were used for analysis of the F2 populations,ratio at the 16.24%level of polymorphism,57 markers were segregation distortion,at a ratio of 13.54%,243 SSR markers were co-dominant,at a ratio of 55.58%.There are 210 SSR markers are codominant,good reproducibility and stablity,which could be used to construct cucumber gentic mapping.(2)A cucumber genetic linkage map of the F2 populations of PI088×CCMC was developed with SSRs.Linkage analysis placed 196 microsatellite loci into seven linkage groups spanning 651.15 cM with a mean marker interval of 3.32 cM.These linkage groups were then assigned to seven corresponding chromosomes.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.According to the disease index of F2 population,two QTLs of downy mildew resistance were detected,one QTL was detected on Chr 4(UW19114～UW019063),the other was detected on Cbr 5(SSR14269～SSR04323),and they explained 13.52%and 22.83%of the phenotypic variation,respectively. |
