Increasing the efficiency of microsatellite discovery from enriched libraries in coniferous forest species

Microsatellites or SSR (simple sequence repeats) are usually single locus, highly polymorphic and robust markers. Microsatellites are increasingly the marker of choice for genome analysis, mapping and diversity studies in plants (Gupta et al. 1996, Westman and Kresovicch 1997) and forest trees (for example Bradshaw et al. 1994, Brondani et al. 1998, Devey et al. 1996). The isolation and development of microsatellite markers, however, is often costly and problematic, especially in organisms with large genomes (Fisher and Bachmann 1998), such as conifers. For example, from our own experience, enriched microsatellite libraries for seven angiosperms (Eucalyptus pilularus, E. globulus, E. grandis, E. cloeziana, Grevillia robusta, Corymbia variegata, Toona ciliata) and three gymnosperm (Araucaria cunninghamii, Pinus elliottii, P. caribaea), using the method of Edwards et al. 1996, yielded enrichment of up to 50% in the angiosperm species but below 10% for all the gymnosperm species. Here we outline a library screening method which recovered high levels of microsatellite containing clones from libraries of coniferous species.