Analysis Of Population Genetic Diversity In Cucumis Sativus L. Var. Xishuangbannanesis And Study On The QTL Mapping Of Fruit Flesh Color In Cucumber

Xishuangbanna cucumber(Cucumis sativus L.var.xishuangbannanesis Qi et Yuan)is one variation found only in China until now.Orange flesh of mature fruit was one of the most important characteristics obviously different from common cucumbers.In this study,Morphological characterization and Simple sequence repeat(SSR) analyses were conducted to assess the genetic diversity in 30 Xishuangbanna cucumber germplasms.Two germplasms were sowed in eight months respectively in order to analyze the influence of environmental factors on sex type of Xishuangbanna cucumber.The nutrition components of 18 Xishuangbanna cucumber germplasms were analyzed during maturation.Genetic analysis of fruit flesh color of two combinations were studied using the joint analysis method of major genes plus polygene of 4 generations.SSR genetic linkage map were constructed and QTL identification were performed for important characters such as flesh color,first female node and so on.The main results are as followed.1 Identification results of 5 qualitative and 13 quantitative characters suggest that there was relatively abundant genetic diversity in Xishuangbanna cucumber at morphological level.Five quantitative characters related to sex differentiation and lateral branch development showed great difference. Based on above data,the result of cluster analysis express that 29 germplasm could be divided into 5 groups,which were basically consistent with important morphological characters.2 Relatively genetic diversity existed in Xishuangbanna cucumber population in molecular level.The percentage of polymorphic loci,Nei's gene diversity(H) and Shannon's information index(I) of 273 samples from 30 germplasms were 92.86%,0.1818 and 0.2972 respectively.The genetic variation among the germplasms was 54.06%and that within germplasm was 45.94%.Cluster analysis showed that the result of classification of most germplasms was consistent with major morphological characters.Among 5 populations according to accession source,the genetic diversity of Jinghong population was the highest.Cluster analyses suggest that the difference of genetic background existed in 5 populations with different collecting source.The coefficient of genetic differentiation(Gst) and gene flow(Nm) were 0.2201 and 1.7718,which indicated that the genetic differentiation was relatively low,with relatively larger gene flow in C.sativus var. xishuangbannanesis.3 The average content of 18 Xishuangbanna cucumbers were as followed:β-carotene 106.58mg/kgDW,lutein 0.48mg/kgDW,Vc4.96 mg/100g,soluble sugar 1.97%,Ca173.21mg/kg, Fe1.28mg/kg,Mg121.89mg/kg,P339.67mg/kg,Zn1.47mg/kg.It was showed that the great difference ofβ-carotene content existed among 18 Xishuangbanna cucumbers.The variation extent and variation coefficient were 1.34～261.55mg/kgDW and 67.68%respectively.With the longer maturation,the p-carotene andα-carotene content intended to be higher and that of lutein showed the adverse trend.Lycopene could not be detected during maturation The accumulation ofβ-carotene induces the orange flesh of Xishuangbanna cucumber.4 Sowed in different months,the lateral stem development of Xishuangbanna cucumber was related with their sex type differentiation.The development of female flower and lateral stem of 2 germplasms expressed opposite tendency.The plant of Xishuangbanna cucumber was sensible to low temperature and short daylight.The optimum sowing date in the protected field in Beijing was from the middle of August to the middle of February in next year.5 There were two major genes controlling fruit flesh color in cucumber.The genes controlling light flesh color(lowβ-carotene content) was dominant to that of orange flesh color(highβ-carotene content).Most variation of relative indexes of flesh color(90.3%～99.3%) was determined by the effect of major genes plus polygenes.For F₂ generation,the heritage of major genes was high (75.97%～99.3%) and that of polygenes(0～23.66%) was low.6 A genetic linkage map based on Xishuangbanna cucumber was constructed containing 74 simple sequence repeat(SSR) markers,which covered 709.9cM of 7 chromosome of the cucumber genome, with an average distance of 9.59cM between adjacent markers.7 Composite interval mapping identified 8 QTLs related with different indexes of flesh color located on 4 chromosoms respectively.Among of them,two major QTLs ofβ-carotene content whose contribution rate were 52.8%and 22.0%respectively were identified on Chromosome 4.Seven QTLs for the characters of the first female flower,resistant to powdery mildew and the number of seeds per plant were located on chromosome 3,chromosome 4,chromosome 5 and chromosome 6 respectively.