ABUNDANCE AND CHARACTERIZATION OF SIMPLE-SEQUENCE REPEATS (SSRS) ISOLATED FROM A SIZE-FRACTIONATED GENOMIC LIBRARY OF BRASSICA-NAPUS L (RAPESEED)

A size-fractionated library of Brassica napus L. (rapeseed), composed of 15 000 clones, was screened for the presence of GA-, CA-, and GATA- simple-sequence repeats (SSRs). GA-SSRs were four- and five-fold more abundant than CA- and GATA-SSRs, respectively, and present at a freque ncy of approximately one SSR for every 100 kb of DNA. Following the se quencing of 124 positive clones, primer pairs were designed and evalua ted for seven selected SSRs. Products were amplified in an array of in dividuals of B. napus, B. oleracea and B. rapa, demonstrating that the seven SSRs were conserved among species. Two SSRs were polymorphic. A mong 11 accessions, the dinucleotide (GA)-repeat, B.n.9A, yielded 12 f ragments, while the tetranucleotide-repeat (GATA), B.n.6A2, revealed t wo fragments. Automated, fluorescence-based detection of polyacrylamid e gels has been employed to simultaneously increase throughput, reduce unit cost, improve analytical resolution, and expedite data acquisiti on of SSR analysis. Though initial financial investment and technical capabilities may prevent some from directly employing our documented a pproach, SSR analysis warrants further investigation as a tool in gene tic studies for enhancing both the conservation and utilization of gen etic resources.