Studies On Genetic Diversty Of Cucurbita Pepo Germplasm Resources

Cucurbita pepo is one of most important cultivated species in Cucurbita, which having a wide range of varieties. The study of genetic diversity analysis of Cucurbita pepo will contribute to germplasm collection and preservation, as well as provide theoretical basis for the study of parentselection, the distribution of genetic diver sity and genetic relationship in pumpkin. The genetic diversity of 64 Cucurbita pepo varieties were analyzed in the present study by using morphological and SSR markers. The main results are as follows:(1)A total of 45 morphologic characteristic The average coefficient of variation was 34.43%, ranging from 6.3% to 70.84%. The average coefficient of qualitative characters(27)and quantitative characters(18) were 35.86% and 32.99% respectively.The umbilicus of a melon has the largest coefficient of variation(70.84%), Leaf shape has the second largest’s(66.77%)and bud shape has the smallest’s(6.3%).The average Shannon’s information index is 1.25, ranging from 0.2% to 4.8%. Qualitative descriptors(1.48) is higher than that based on quantitative descriptors(1).The maximum of diversity index is thickness of the seed(4.8), the minimum of H ’ values are quality of seeds and seed width(0.2).(2)The 64 Cucurbita pepo germplasm were divided into 2 groups based on the morphological data.the one for naked kernel zucchini, and the other for the crusty zucchini, according to other mainly different morphological characters of germplasm,the inside groups were further classified.The result of principal components analysis that divide the test material into two categories is the same to the result of cluster analysis, it showed that variance contribution rate of the first, second and third main coordinates are respectively 21.16%, 13.49% and 7.93%, an d the cumulative variance contribution rate of 42.58%.(3)35 pairs of primers produced 157 seorable by using SSR marker, of which 145 bands(92.36%) were polymorphic across 64 pumpkin accessions. The mean of 4.49 bands and 4.12 polymorphic bands per primer pair was detected.The average Shannon’ s Information index of SSR loci was 0.89,ranging from 0.2 to 3.8.(4)Based on the method of hierarchical cluster analysis by SSR data, it showed that genetic similarity coefficient of 64 pumpkin was ranged from 0.73 to 1,which were clustered into 2 groups(naked and crusty), as the same as the cluster analysis of morphological traits. The basic classification of internal groups were locality and whether vine germplasm or not.The result of principal components analysis showed that accumulative variance contribution first three principal components was 26.79%, the variance contribution rate of the first, second and third prineipal were respectively 10.61%, 8.77% and 7.41%,but its main ranking position coordinates was very messy, and 64 pumpkin material could not be classified.(5)The analysis result of Mantel test about the morphological markers and SSR markers showed that the correlation coefficient was 0.4647, which indicated two markers for the classification of the test material had a low consistency.