Studies On Genetic And Polysaccharide Diversity In Cucurbita Germplasm Resources

Pumpkin (Cucurbita) is one of the major vegetable crops in Cucurbit family. Due to its easy cultivation, high yield, long shelf life and abundant nutriments, pumpkin is very popular in China. In this paper, 70 accessions in cucurbita from different countries or regions were analysised by using morphological and RAPD markers. The study on the genetic diversity in cucurbita can benefit the conservation, classification, identification, genetic enhancement and effective utilization of cucurbita germplasm resource. In this paper, aiming to select Pumpkin which has high content of polysaccharide, we also discussed the diversity of the different pumpkin polysaccharide from several aspects including the extraction, purification, identification and physiological activity. The polysaccharide analysis of 56 accessions provided some useful information and facilitated the selection of pumpkin breed possessed biological activity. The main research contents and results were as follows:1. In 45 morphological assessments, the average coefficient of variation was 32.16%. The average Shannon's Information index among the assessments was 1.25. The 70 accessions were clustered into 3 groups based on the morphological data: Cururbita moschata, C. pepo, C. maxima. The results of principal components analysis showed that the accumulative variance contribution of the first three principal components was 67.31%. The characteristics of fruit stem, seed and flower, fruit shape and growth habit are the primary factors affecting cucurbita germplasm classification according to morphological characters.2. Twenty one random primers which used in the experiment produced 168 consistent and differential amplification products. Among them, 157 bands (93.5%) were polymorphic. Cluster analysis revealed three clusters: Cururbita moschata, C. pepo, C.maxima. This conclusion is completely consistent with the traditional cultivar classification. And within C.moschata, the dendrogram shows the existence of three sub clusters. Within C. pepo, the dendrogram shows the existence of six sub clusters. Within C.maxima, the dendrogram shows the existence of five sub clusters. This conclusion is correlative with their origins and morphotypes. Principal coordinate analysis also revealed three clusters. The results from these two methods were similar.3. Comparison of the data obtained by morphological markers and molecular makers was made by the method of Mantel test. The r correlation value scope was 0.6306 between the morphological markers and molecular markers; A consensus tree based on morphological marker and molecular markers was produced by CONSEN module in NTSYS. The result shows that there are some difference and also some comparability between the genetic relationship among cucurbita accessions revealed by RAPD and that by morphological markers.4. In order to study the hot water extraction and microwave extraction technology of Pumpkin polysaccharide, we used the methods of single factor test and orthogonal design test of L9 (3⁴) and their antioxidant activities were studied simultaneously. The result showed that the highest extraction rate of Pumpkin polysaccharide by hot water extraction could be obtained with a ratio of solid to liquid with 1:40, 70℃for 4h and 3 times extraction. In microwave extraction technology, the optimal conditions were as follows: the radio of solid to liquid with 1:30 and the extraction time of 20min under the microwave intension of 60%. In contrast to the hot water extraction method, the extraction rate of the microwave technique was higher and the extraction time was shorter. Meanwhile, anti-oxidative results showed Pumpkin polysaccharide extracted by the two methods was effective to anti-oxidation.5. The scavenging effect of Pumpkin polysaccharide on·OH and O₂^-were studied. The result showed that Pumpkin polysaccharide had a significant effect on scavenging·OH and O₂^-. It could inhibit the generation of MDA in liver homogenate, the swelling of mitochondria and hemolysis of RBC induced by·OH. The conclusion was that Pumpkin polysaccharide had the effect of anti-oxidation induced by OH.6. Polysaccharide was extracted from 56 cultivars of pumpkin, and their composition and activity were analyzed. The results showed that there were obvious differences not only in extracting rate, but also in content of neutral sugar, uronic acid of PP, which led to different inhibiting effects on hydroxyl radical (·OH) and superoxide anion radical(O₂^-).In conclusion, diversity existed in characteristics and bioactivities of PP among pumpkin cultivars. The 56 accessions were clustered into 4 groups based on the composition and activity data of PP by the method of principal coordinates analysis. In the fourth group, 3 accessions content of PP and inhibiting effects on hydroxyl radical (OH) and superoxide anion radical(O₂^-) are also better.7. Two PP from two different pumpkin varieties were graded by DEAE-52 cellulose column and Sephadex G-200 column. Six components, ZPPla, ZPP2, ZPP3, YPP1, YPP2, YPP3a were obtained. By UV spectrum analysis, six components were shown to be homogeneous. Their physical, chemical characters, composition and activity were studied, and their structures were analyzed by IR (Infra-Red) spectra. The results showed that there were typical characteristic absorption peaks of polysaccharide in their spectrograms. It testified that the six components were polysaccharide. The results also showed that diversity existed in characteristics and bioactivities of six polysaccharide components between H34 and 02-4. In conclusion, 02-4 is prior to H34 and could be a useful breeding germplasm.