Studies On Genetic Diversity Of Spaghetti Squash (Cucurbita Pepo) And Relationship With Cucurbita Genus

Spaghetti squash, a special novelty vegetable crop of Cucurbita, is becoming more and more popular. when cooked, freezed and salted, the flash with golden color falls away from the fruit in ribbons or strands like spaghetti. Besides spaghetti squash’s nutrition components are very rich, especially in protein, vitamins and minerals. However, little is know about it’s genetic background. The study on genetic relationship and diversity of spaghetti squash can provide more information for germplasm resources protection, plant breeding and parental guidance matching. In this study,56 spaghetti squash accessions collected from China and abroad were subjected to be morphologically evaluated and another 32 cucurbita cultivars accessions were joined to analyze genetic diversity and relationship at molecular level. According to the experiment, we drew the following conclusions:1.According to 21 qualitative and 16 quantitative traits of spaghetti squash, the average variation coefficient among 56 accessions was 37.5% and 22.1%, respectively. For most traits the variation coefficient was ranged from 30% to 50%. The minimum variation coefficient was 4.46% for the number of fruit stripe and the maximum was 61.5% for leaf notches. Morphological characters with more variance were usually related to the fruit. On the basis of morphological characteristics, the 56 accessions were distinctly classified into 2 major clusters; 23 varieties were grouped as cluster Ⅰ, and another 33 accessions were categorized under cluster Ⅱ. Principal components analysis (PCA) base on all traits revealed that two principal components can explain 33.794% of the total variation. The characteristics of fruit size and shape are primary factors affecting spaghetti squash germplasm classification to morphological characters and plant growth habit followed.2.Analysis based on molecular marker revealed that:(1) There were 50 SRAP primer pairs selected from 285 primer pairs, which amplified a total of 713 bands via PCR. Amongst them,586 bands were polymorphic with a percentage of 88.92%, which suggested that Cucurbita genus was rich in genetic diversity. (2) There were 586 bands generated within the 56 spaghetti squash accessions.350 (59.7%) of these bands were polymorphic, which revealed that the genetic similarity of spaghetti squash cultivars was high. (3) the 56 spaghetti squash accessions could be clustered into five major sub-groups, according to the analysis on genetic similarity coefficient. Spagetti squash had the closest genetic relationship to C.Pepo; a closer relationship to Cucurbita moschata whearas its relationship with C. Maxima was farthest. According to the above results, we couldconfirm that the spaghetti squash could be regarded as a subspecies of C. pepo.(4) Analysis based on the SRAP data of hierarchical cluster revealed that the genetic simility coefficient among spaghetti squash cultivars is very high, so it is had to distinguish different type of cultivars. However it can obvious founded that compare with C.maxima and Cucurbita moschata the genetic relationship between spaghetti squash and C. pepo is very close.3. System analysis of the date obtained by morphological markers and molecular markers revealed that:The correlation value have a certain similarity between the morphological markers and molecular markers, such as many varieties with the same background together. And there are big difference among them. Such as the result of morphological analysis can be obvious distinguish with the fruit average weight and the plant vine, while the SRAP molecular markers analysis different cultivars based on genetic differences and geographical variations.