Identification Of Cucumber Powdery Mildew Resistance Of Chromosome Segment Introgression Lines And Prediction Of Candidate Gene

Powdery mildew is one of the three major diseases in cucumber (Cucumis sativus L.), which will not only reduce the photosynthetic efficiency, but also effect the yield and fruit quality of cucumber. Hence, breeding of cucumber resistant to powdery mildew has become one of the main goals of breeders. By identification of natural infection in the field and artificial inoculation with powdery mildew, we have got a high resistance to powdery mildew inbred line JIN5-508(sprawling, DI=0) and high susceptible inbred line D8(drawf, DI:near38). Using JIN5-508and D8as parents, taking D8as the recurrent parent for continuous12generations of backcrossing and selfing, we have obtained17chromosome segment introgression lines on the genetic background of D8.1. Phenotypic characteristics of introgression lines and their parents were investigated.The height of introgression lines were obviously dwarfed when compared with JIN5-508, and were similar to D8, or even even shorter. During the repeated backcross with D8processes, the special characters of dwarf tend to recurrent parents in genetic background. Differences in segment introgression lines and D8mainly lie in the ability of resistance to powdery mildew. Different introgression lines showed different powdery mildew disease index, and64.71%of introgression lines were siginificant inferior to D8(5%level).2.324pairs of SSR primers, which uniformly distributed on7chromosomes, were used to investigate introgression lines.74SSR primers showed polymorphism between JIN5-508and D8, accounted for22.8%.7resistant fragments related to powdery mildew resistance were identified, located on Chr.l29.3cM～30.0cM (0.7cM) and41.3cM～43.3cM (2.0cM), Chr.20.0cM～3.9cM (3.9cM), Chr.354.0cM～55.9cM (1.9cM) and77.1cM～78.2cM (1.1cM), Chr.434.4cM～35.1cM (0.7cM) and Chr.61.8cM～3.2cM (1.4cM), the frequencies were61.9%,11.1%,14.3%,33.3%,65.1%,7.9%and11.1%. In the63resitant to powdery mildew single plant, single segment, double segment, three segments and four segments introgression lines were13,31,16and3strains, accounted for20.6%,49.2%,25.4%and4.8%, respectively.3. Candidate genes were predicted in the target fragments of Chr.l29.3cM～30.0cM (0.7cM) and Chr.377.1cM～78.2cM (1.1cM) regions. Physical distance of0.7cM fragment is96.3kb, and15candidate genes were obtained, in which only4genes were associated with disease resistance; Physical distance of1.1cM fragment is290.6kb,50candidate genes were obtained, in which only8genes were associated with disease resistance.