Genetic Diversity of Watermelon Germplasm Revealed by SSR Marker

Plant Introduction constitutes one of the most important approaches for plant breeding, especially on watermelon, as there is little evidence on watermelon origination in China. Besides watermelon production plays an economically important role in China for farmers. However, the success of watermelon domestication pattern is determined by its ecotype and genetic characteristics.Therefore, in this experiment, both of the genetic diversity and relatedness on watermelon grouped by ecotypes were examined using 96 watermelon cultivars, landraces, lines, hybrids and wild types collected from China, Japan, Russia as well as America respectively based on SSR markers. Total of 38 pairs of primer with polymorphism were chosen from 398 SSR markers and produced 139 loci with 69 polymorphic loci (49.6%) as well as 1.8 polymorphic loci on average.Jaccard's similarity coefficient (JC) which was demonstrated by pair-wise comparisons of genotypes ranged from 0.42 to 0.99. A dendrogram was constructed using the Unweighted Pair Group Method with Arithmetic averages (UPGMA) in computer program NTSYSpc Version 2.02i. 96 watermelon genotypes were classified into VII groups at similarity coefficient of 0.74 by ecotypes according to the Cluster Analysis. Group I comprised 35 watermelon germplasm from Northern area of China which have types of intermediate maturity periods and low level soluble solids content as well as mushy flesh texture. Group II contained 2 watermelon germplasm from Northwestern and 8 watermelon germplasm from Southern area of China with large fruit size and thick rind. Group III included 2 types of vegetable watermelon germplasm, featuring large seeds size, white flesh and low soluble solids content. Group IV included all watermelon germplasm from Northwestern area of China which performed to be thick in rind, long on maturity period and high with soluble solids content. Group V consisted 3 different types of watermelon germplasm from Japan, Russia and America while 2 semi-wild types were grouped into the sixth cluster. The wild type watermelon germplasm formed a distinct cluster. These results indicated consensus with the geographical distribution of watermelon germplasm in China on the basis of SSR markers. The exception was that watermelon from Northwestern and Northern area of China was grouped in the same cluster. Watermelon germplasm from different countries (Japan, Russia and America) were also classified into the same group. But all these results further suggested that the narrow genetic basis of watermelon and all watermelon germplasm collected from China will have benefit to broaden the materials of watermelon in genetic breeding.