| Expressed sequence tags, increased rapidly in number recently, are important resources for development of molecular markers. Compared with common makers derived from genomic DNA, the EST-derived maker is a novel type of molecular maker and has remarkable advantages, such as simpler development, more information, highly transferable and so on. These markers were applied in many fields,eg. comparative mapping, genetic diversity evaluation and phylogenetic analysis et al..Howerver, there is still only a few of species whose EST-derived makers have been developed and applied.Brassica napus L., as one among them, is one of main oilseed crops, and thereby, so many markers has been applied in rape for new variety breeding, which are based on DNA of genome, yied, trait, hardiness improving and genetic research. But, until now there is no researcher who has applied EST-derived markers of rape, even if developed.The study analyzed SSR recouse of ESTs data in oilseed rape, and preliminarily developed some EST-SSR makers. Moreover, these markers were tested to applied in anlysis of gentic diversity, providing some referecence on rape breeding. The result as below:(1) 63334 ESTs, from the EST database of NCBI of oilseed rape, were downloaded and processed, resulting in 17987 non-redundant ESTs with total length about 12165.38kb.Totally 2803 SSRs distributed in 2443 ESTs were mined out, accounting for 15.58% of the non-redundant ESTs. The average length and distribution distance of the EST-SSRs were about 18.84 bp and 4.34 kb respectively. Dinucleotide and trinucleotide repeats, with similar frequency and accounting for 89.05% together in all SSRs, were the main types. AG/CT and AAG/CTT are the most frequent motifs, accounting for 84.04% and 35.71% in dinucleotide and trinucleotide repeats respectively. The availability of the EST-SSRs was also assessed based on the potential polymorphism and possibility for designing primers specific to flanking sequences of SSRs contained in the ESTs.(2) According to 2083 EST-SSR, 23 primer pairs for EST-SSRs were designed and the suitable annealing temperature for each primer pair was determined by gradient PCR. The amplification and polymorphism displayed by these primers in 10 varieties of oilseeed rape were detected by using silver staining of nondenaturing polyacrylamide gel. 21 primer pairs showed the amplification, accounting for 91.30% of total primers, and 12 primer sets showed polymorphisms, accounting for 57.14% of primers available. These results indicate that it is an effective and feasible approach to develop SSR markers based on ESTs in oilseed rape.(3) 21 EST-SSRs markers were developed to detect genetic diversity of oilseed rapes among 42 varieties. Analyzing Oilseed rape, they could reveal differences in expression of correlative gene among varieties. Eighty five alleles were checked among the 42 varieties, of which 49 alleles accounting for 57.65% showed polymorphic. The range of the 42 varieties' genetic distance was between 0.0087-0.3190 computed by NTSYS (software) , On level of genetic distance 0.1508, the varieties were divided into 5 groups, which was approximately in accordance with their diversity of cultural area, and provided a scientific basis for selection of parents for hybridization of oilseed rape.
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