The SSR Markers Linked To Downy Mildew Resistant Gene In Melon (Cucumis Melo)

Downy mildew caused by Pseudoperonospora cubensis. Downy mildew is a major foliage diseaseof cucurbit crops in the world. During favourable environmental conditions,the pathogen can defoliateplants and destroy entire fields within a week.Currently, the principal method of controlling this diseaseis the use of protective fungicides. Unfortunately, some fungicides have lost their efficiency due to thedevelopment of resistance by the fungi. Development of cultivars with inherent resistance to downymildew is the most effective and economical approach to control downy mildew.The line PI414723(highly resistance to downy mildew) as female parent and the line DF4(highlysusceptible to downy mildew) as male parent were used to construct F2segregating populations. Theinheritance of downy mildew of PI414723is studied.Combining with bulked segregation analysis（BSA）and SSR analysis is used to find the molecular makers linked to downy mildew resistant gene.The main results are summarized as the followings:（1）The identification experiments were carried out in greenhouse by artificial inoculations inadult stage. The parental lines PI414723‘and DF4‘behaved, as expected, according to resistance andsusceptibility.In F2segregating populations, the result showed that119plants performanced resiatantand37plants performanced susceptible, which closed to segregation ratio of3:1. It indicated that theresistance of the line PI414723to the downy mildew was controlled by one pari of dominant gene.（2）Among the211SSR primers tested,136were polymorphic between PI414723‘and DF4‘.The polymorphism rate was64.5%. According to the identification result of F2segregating populations，the BSA method was used to establish the resistant and susceptible pool. Among the136SSR primerstested, There were six SSR makers with polymorphism between the resistant with susceptible pool. Sixmakers amplificated in F2populations. The QTL IciMapping software was used for linkage analysis, theresult showed that linkage distance between the downy mildew resistance gene with the marks(DE1887、DE1320、DM0854) were26cM、26cM、13.69cM, respectively.