| Applying heterosis and breeding varieties for diseases-resistance are the major goals in melon (Cucumis melo L.) and watermelon (Citrullas lanatus L.) breeding.Purity identification of F] hybrids in melon and watermelon is a critical activity for seed companies and seed laboratories. Up to date, commonly phenotypic identification is based on morphological traits recorded in the field through grow-out test (GOT). However, this method involves a lengthy survey of plant growth that is costly, labor intensive, and vulnerable to environmental conditions. As an alternative, DNA molecular markers can be used to determine the purity of hybrids based on the paternal-specific bands and maternal-specific bands presented in FI plants. The advantages of this technique are its ability to detect extensive polymorphisms, simplicity and rapidity. Here we report the application of RAPD and SCAR markers for the identification of hybrids in melon and watermelon.Diseases have always been a concern in melon and watermelon production, or even a threat in some regions. Planting cultivars for diseases-resistance are the first strategy. In the process of selecting resistant progeny among segregation population, plant breeders often fail to complete task alone due to the lack of condition and knowledge in plant pathology. Markers assisted selection (MAS) for disease resistance offer the additional advantage of permitting selection for resistance in the absence of the pathogen, or in the case of pathogens that exhibit inconsistent expression due to environmental or other factors. This feature is of particular interest to a plant breeder who may be reluctant either to work directly with or to introduce a pathogen where quarantine restrictions prevent its introduction. Thisapproach would greatly facilitate selecting for disease resistance and speed up the pace of advance in melon and watermelon breeding.Two experiments were included in this research: (i) Developing a technique to determine purity of hybrids of melon and watermelon using DNA molecular markers; (ii) F2 population (Hong Xuncui X Hong-28) were screened by ISSR primers for finding molecular markers linked to powdery mildew resistance gene in melon with methods of Bulked Segregant Analysis (BSA).Ten primers, with which polymorphic bands could be amplified between two DNA pools of the parents of four melon hybrids, were screened out from 220 RAPD primers in parents of five melon and three watermelon hybrids. These ten primers could generate three to five brighter bands including polymorphic bands, the size of amplified DNA fragments with the ten primers ranged from 400 to 2000 bp. Then these ten primers were used to amplify the total DNA of each FI hybrid to determine their specificity and stability, respectively. A primer MHD06 could amplify a paternal specific band and a maternal specific band in hybrid 1-36, primer OPQ9, OPN14, OPQ19, OPS11 and OPR13 could only generate paternal-specific bands in hybrid 1-31, respectively. Also, paternal-specific bands were amplified with primer OPR4 and OPV14 in Lu-Baoshi, and with primer OPS 13 in XiYu No.l, respectively, while maternal-specific bands were generated with primer OPG12 in hybrid 1-36 and with OPS11 in hybrid 1-31, respectively. But all primers fail to detect any polymorphism in the other melon and three watermelon hybrid combinations.In order to determine the reliability of amplified product as molecular markers, the amplification with the ten RAPD primers was repeated at least ten times. Only five primers including MHD06, OPQ9, OPN14, OPR4 and OPS 13 could stably produce reproducible specific bands in corresponding FI hybrids in multiple runs, respectively. Each of these five primers was used to identify purity of appropriate hybrids at 100 plants of FI respectively. The percentages of hybrid plant quantities in total F1 plants were 95.9% in hybrid 1-36 with MHD06, 93.7% and 94.8% inhybrid 1-31 with OPQ9 and OPN14 respectively. By contrast, the percentages of hybrid 1-36 and 1-31 phenotypic iden...
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