| Three molecular marker techniques RAPD, SSR and AFLP were employed to analyze the genetic relationship among 26 watermelon accessions. In addition. The purity of the popular watermelon variety "Jingxin No. 1" and ice-box-watermelon variety "Jingxiu "were tested by molecular markers.". The main results were as following:(1) Informative data from RAPD, SSR and AFLP analysis were applied to elucidate the relationship of 26 watermelon accessions, respectively. The results of cluster analysis according to three molecular marker systems were compared. On the basis of cluster tree, these accessions were classified into 6 groups, i. e. one East-Asia group,one American group,two medial groups and two African wild groups. Meanwhile, the relationship among ecological types and various varieties were analyzed in detail, and the result was agreed with the origin and morphological traits of these varieties.(2) The results illuminated that the genetic diversity among watermelon cultivars is low .It emphasizes the need to expand the genetic base of cultivated watermelon in future breeding.(3) In RAPD analysis, 14 random primers were screened to produce the fingerprint of 26 watermelon materials. These primers or primer combinations could be used in identification of the each watermelon accession except for several near-related materials. The most of materials have their specific fingerprint.(4) The purity of watermelon variety "Jinxing No. 1" was. Identified by the Two RAPD markers OPN04/600bp and OPK14/1500bp effectively.,Moreover, these two RAPD markers were successfully transformed to SCAR markers SCK14/1500bp and SCN04/600bp.The veracity of SCAR maker identification is same as field testing in "Jingxing No. 1". The result showed that SCAR makers could be effectively used in hybrid purity testing.(5) A SSR marker "IX-690bp" amplified specially from the F1 hybrid "Jingxiu" and its male parent could be used as a specific marker to identify hybrid purity of "Jingxiu" in commercial seed production.
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