Exploitation Of EST-SSR And Construction And Integration Of The Genetic Maps Of Watermelon

EST-SSR is a new type of molecular marker developed from the databank of sequence of expression sequence tags (EST) and/or cDNAs. As a new kind of molecular marker, EST-SSR markers have more advent- ages than the traditional genomic-derived SSRs because they are part of expressed genes. Therefore, EST-SSRs might be involved in gene functioning directly or indirectly. The ability of SSR markers will be greatly enhanced. In this study, we design primer pairs based on the searching the EST database of NCBI. And we locate these EST-SSRs on the map from the PI296341 and 97103 watermelon genotypes used as parents for the mapping populations. Then we map these EST-SSR markers on the genetic linkage map using a recombinant inbred population of watermelon, RIL-8. The main results are as follows:1. A set of 36 simple sequence repeats (SSR) primers has been developed in watermelon from genomic libraries (gSSR). Through PCR amplifications and silver detection, 32 primer pairs had successful and distinctive bands in different varieties of watermelon.2. From 820 ESTs of watermelon , we have identified 87ESTs containing perfect simple sequence repeats (EST-SSR) of di-, tri-, tetra- or pentanucleotides .The most abundant SSR types are Trinucleotide and dinucleotide repeats .Among dinucleotide repeat, the motifs of AG, GA, CT and TC occur more frequently.3. 79 EST-SSR primer pairs were designed for watermelon based on the searching results.Through PCR amplifications and silver detection, 36 primer pairs had successful and distinctive bands in different varieties of watermelon. These EST-SSR markers can as a new molecular marker of watermelon and related species.4. A linkage framework genetic map was constructed by 16 SSR markers 9 EST-SSR markers and. The map length is 174.428 cM, distributed in 5 linkage groups, and map density is 6.977cM/marker.5. Map merging: In this study, we use the same population the map of Yi Ke constructed in 2004.Then we integrated the map with Yi Ke's map. After map merging, a composite geneticmap was obtained including 194 transferable markers: 65AFLPs, 30 SSRs, 81 RAPDs, 5 ISSRs, 2 SCARs, 9EST-SSR , the W^f locus and Su^bi locus. The map length is 763.466 cM, distributed in 17 linkage groups, and map density is 3.935 cM/marker.6. This study is the first exploitation and utilization of EST-SSR marker which derived ESTs of watermelon and constructed genetic map utilized EST-SSR and SSR markers. The study provide with innovation to EST-SSR marker exploitation and genetic map merging of watermelon and other species of Cucurbit family.