Study On Phenotypic Diversity Of Watermelon (Citullus Lanatus)Germplasm Accessions

Watermelon germplasm is not only important gene source for genetic modificationbut also important material basis of cultivar improvement for high yield, superiorquality and resistance to diseases and pests. It is commonly agreed that the nativeorigin of watermelon is in Kalahari Desert and its peripheral sabana tropical grasslandborderland zone in South Botswana in Africa. Long-term artificial selection andcultivar (especially hybrids) extension has made numerous watermelon germplasmmissing. Modern watermelon breeding programs thus build on quite weak materialssources and are less effective. In order to effectively use watermelon germplasmaccessions, and to breakthrough germplasm bottleneck of watermelon improvement,we should research continuously and in-depth watermelon germplasm resources andtheir utilization. Experimental materials of768watermelon germplasm accessionsfrom the National Engineering Research Center for Vegetables were used in the study.Under the open field conditions,11quality characters and13quantitative characterswere recorded and analyzed via the methods of phenotypic diversity, correlationanalysis, principal component analyses and cluster analysis.The results weredemonstrated as follows:1. Watermelon main botany traits phenotypic diversity is very rich: phenotypicdiversity of768Watermelon germplasm accessions in main characters tested showedCV ranging from0.32%(Distance between female flower to the growing point) to73.32%(Seed speckle shape) with an average of32.41%. The average of768watermelon genetic resources characters diversity indexes (H′) is1.6. The higherdiversity indexes (H′) are pulp texture(2.12), distance between female flower to thegrowing point(2.06),flesh solids content (2.04),100-seed-weight (2.02),leaflongitudinal diameter(2.02),seeds per fruit (2.01),and the least one is Stem sectionshape(0.4).2. The correlation analysis on the Watermelon agronomic characters showed thatthere were very significant positive correlations(p≤0.01) between51pairs characters, such as fruit development period and whole growth period, distance between femaleflower to the growing point and length between nodes，leaf longitudinal diameter andleaf transverse diameter.; very significant negative correlations between29pairscharacters, such as peel thickness and flesh solids content,100-seed-weight and seedsper fruit; significant positive correlations(p≤0.05) between10pairs characters, suchas whole growth period and leaf longitudinal diameter，length between nodes and100-seed-weight；significant negative correlations between3pairs characters, such aswhole growth period and fruits’ longitudinal diameter, plant resistance type and fleshflavor.3..In watermelon germplasm accessions phenotypic traits, principal componentanalysis contains a limited amount of information.22characters components weresummarized into8principal components which cumulative contributive rateaccounted for63.769%. The eight principal components from high to low were fruitshape factor, flavor factor, growth period factor, Leaf shape factor, seed factor, growfactor, sex factor, and seed coat factor.4. Watermelon germplasm accessions cluster analysis results complex. It wasclassified into two categories by cluster analysis as the genetic distance was25: A wasCitrullus lanatus (Thunb.)Matsum et Nakai, it compared with the botanicalclassification in “xinjiang Melon and watermelon” writen by Lin Depei et al(the samebelow); B was Citrullus colocynthis (L.) Schrad.; It were classified into fourcategories by cluster analysis as the genetic distance was20: A1wasvar.vularis; A2was var.capensis (Alef.) Fursa; A3was var.mucosospermus; B was sp.insipidus(Pang.)Fursa. When the euclidean distance was15and10, it was divided by varietiesgroup.