Development and genetic mapping of microsatellite markers from genome survey sequences in Brassica napus

Microsatellite or simple sequence repeat (SSR) markers are routinely used for tagging genes and assessing genetic diversity. In spite of their importance, there are limited numbers of SSR markers available for Brassica crops. A total of 627 new SSR markers (designated BnGMS) were developed based on publicly available genome survey sequences and used to survey polymorphisms among six B. napus cultivars that serve as parents for established populations. Among these SSR markers, 591 (94.3%) successfully amplified at least one fragment and 434 (73.4%) detected polymorphism among the six B. napus cultivars. No correlation was observed between SSR motifs, repeat number or repeat length with polymorphism levels. A linkage map was constructed using 163 newly developed BnGMS marker loci and anchored with 164 public SSRs in a doubled haploid population. These new markers are evenly distributed over all linkage groups (LGs). Given that the majority of these SSRs are derived from bacterial artificial chromosome (BAC) end sequences, they will be useful in the assignment of their cognate BACs to LGs and facilitate the integration of physical maps with genetic maps for genome sequencing in B. napus.