Analysis Of Genetic Diversity And Construction Of Primary Core Collection Of Seed Watermelon Germplasm Resources

Seed watermelon(Citrullus lanatus ssp. vulgaris var.megalaspermus Lin et Chao.)is a kind of important economic crop which seed as the main edible organs.For a long time,with the expandsion of cultivated area, the increase of multiple cropping index, the serious disease of seed watermelon and no regulate the conventional breeding,it lead to be mixture of seed watermelon variety in a degree and to be serious a decline in the quality and yield instability.So it is very important to identify and classify the seed watermelon accurately,and select the important and rare variety to improve the seed watermelon breeding.The study applied the phenotypic traits combined with SSR molecular markers to analyze the genetic diversity and genetic relationship of 50 seed watermelon germplasm from different regions of China and foreign region, then the core collection was constructed from agronomic traits and DNA molecular level. The main results are as follows:1.The average coefficient of variation of 39 botany traits was 32.24%, flesh color of the coefficient of variation was the largest in 75.88%,fruit development period of the coefficient of variation was the smallest,only 6.88%;39 botany traits of Shannon’s information index averaged 5.47, its change range was from 2.58 to 5.64.2.The cluster results based on phenotypic characters showed that the wild type and common watermelon germplasm were clustered into one group.Seed watermelon germplasm collection was clustered into one group;In the principal component analysis, the first principal component mainly reflected the characteristics of plant leaves, the second principal component mainly reflected the characteristics of seed, the three main points mainly reflected the flesh color and soluble solids, and The classification results of principal component analysis and cluster analysis were basically consistent.3.Based on the sampling proportion of 10% to 70%, the non weighted average method and the preferential sampling method were used to construct the core subset.The evaluation parameters of the four core collection parameters were compared, which were the core subset in the mean difference percentage, the variance difference percentage,the difference between the range and the rate of variation coefficient.4. By comparing the core collection and the original group in the mean, range, variation coefficient, variance and genetic diversity indexes of the five value differences had fully proved that the core germplasm was more representative of the original population genetic diversity.5.31 pairs of primers were selected from 106 pairs of primers for SSR marker analysis.31 primers amplified a total of 138 bands, of which 115 were polymorphic bands, the polymorphic bands ratio was 83.33%; the Shannon diversity index of random primers was 0.4193.6. Based on cluster analysis of SSR molecular markers, similar coefficient among germplasm was 0.57 to 0.91,genetic relationship between seed watermelon germplasm wild and vegetable watermelon germplasm and was far away, and the genetic distance between seed watermelon germplasm very narrow.When similarity coefficient was 0.657 office,50 seed watermelon(watermelon) can be divided into 6 groups,it was wild watermelon germplasm,watermelon germplasm and seed watermelon germplasm,respectively,these could be clearly distinguish.Based on the classification results of SSR markers generated by the principal component analysis showed that 50 seed watermelon(watermelon) germplasm were divided into 4 groups,29 (wild watermelon) and 33 (PI542120) alone divideed into a group,5(Heibengjin) alone can a group, it showed that the three copies of germplasm and other germplasm genetic distance was far, the other 47 germplasm clustered closely together.7. The primary core collection was constructed by Least Dinstance Stepwise Sampling (LDSS) to build a core subset based on SSR molecular markers.In a total of 7 times sampling, with the number of sample ing reducing, changes of genetic diversity was small in the overall.the changes on number of effective alleles was small, and the number of effective alleles was the highest in sample 6. Nei’s gene diversity index (H) and Shannon’s information index (I) were slightly increased, and the highest value reached the highest value in sample 6.The percentage of polymorphic loci showed a downward trend, which decreased significantly in the sample 7. According to the above analysis,FZ20 were taken as primary core collection.the results proved that the core collection can represent the genetic diversity of the original collection.