Study On Parthenocarpy And Genetic Diversity Of Cucumber With ISSR Markers

Cucumber(Cucumis sativus L.) is a very important vegetable crop with an adundant germplasms. Researches on evaluation and classification of cucumber germplasms with molecular markers play an important role in innovation of germplasms and breeding for new varieties. It hasn't been reported that ISSR is used to indentify cucumber germplasms and genetic diversity . Orthogonal design was used to optimize the cucumber ISSR reaction system in the present research. Parthenocarpy is one of important economic characters and has been an important aim character in the field of modern cucumber breeding. Based on the separate progeny from the cross between parthenocarpic line EP-6 and non-parthenocarpic line ZR-2, 135 individuals were tested in molecule characters linked with parthenocarpy. 46 cultivated accessions were used in this study to analyze their polymorphisms with ISSR primers. 42 polymorphic ISSR bands were amplified with 8 ISSR primers. Genetic similarity coefficients were calculated by Jaccard method and culstering was conducted for 46 cultivars by UPGMA.The DNA fingerprinting of hybridity with ISSR markers were contructed preliminarly in three cucumber crosses . The main results were as follows:1 In this study, Orthogonal design with three levels of four factors(Taq DNA polymerase,dNTPs,primer,Mg²⁺) was used to optimize the cucumber ISSR reaction system. The results showed that a better amplification of ISSR was obtained with the reaction system containing 1×PCR buffer,1.5mmol/L Mg²⁺,25ng DNA,ddH2O,1UTaq DNA polymerase,200μmol/L dNTPs,0.75μmol/L. It provided the basis for the analysis of diversity, map construction and gene localization of important traits in cucumber with ISSRmarkers. 2 The separate progeny from the cross between parthenocarpic line EP-6 and non-parthenocarpic line ZR-2 was employed to screen the molecular markers linked to the parthenocarpy of cucumber with the method of BSA(bulked segregation anlysis). A band of 850bp was tested not only in two parents but also in two DNA pools with the primer N92. The product of electrophoresis with the primer N92 showed that non-parthenocarpic line had the band but parthenocarpy line none. Therefore the primer N92 could be used to identify cucumber parthenocarpy. It provided the basis for marker assistance selection in breeding and gene localization of cucumber parthenocarpy.3 With 8 ISSR primers, 42 bands were amplified in 46 cultivated accessions of cucumber, of 36 bands (85.71 %) were polymorphic. The genetic similarity coefficients of 46 cultivated accessions were ranged from 0.3030 to 0.8750, the coefficient(0.3030) between 23(ZN1)and 42(SichuanCunjinzi)was the lowest, meaning the longest genetic distance between them and the highest coefficient was found between 34(Edipse)and 43(Yangjing),meaning the shortest genetic distance between them. The culstering of 46 cultivated accessions showed that the cultivars are divided into 2 groups at the threshold of 0.52 and was realted to the sex phenotypes of cucumber. One group was charactered with more gynoecious phyenotypes ,and the other for general sex phenotypes. 46 cultivated accession were culstered four groups at the threshold of 0.54. Most of the same ecotypes could be grouped into same group and subgroup. Cultivar charactered by the specific band for parthenocarpy was found in different groups and the parthenocarpy accession of the first three groups accounts for 46.10%. It suggested that parthenocarpy of cucumber exist widely, but differences in this character be in various accessions.4 65 ISSR primers were used in three cucumber crosses, and of 5 primers showed polymorphisms in parents and their F₁. Primer J1,UBC818,N86 and I-10 have polymorphic bands in the cross1, and the specific bands of parents were found in their F₁. Polymorphisms could be found in the cross2 and cross3 with two primers(N86 and I-10),and the specific bands of parents were found in their F₁.The DNA fingerprinting of hybridity with ISSR markers were contructed preliminarly. It provided a new technique for distingishing uniform and a molecular basis for protecting intellectual property rights of new cucumber varieties.