Microsatellite retrieval in lettuce (Lactuca sativa L.)

By using enriched genomic libraries, microsatellite-containing sequences we re isolated from lettuce (Lactuca sativa) with high efficiency. With this a pproach, a sizeable fraction (up to 55%) of the clones contained a microsat ellite. In about half of these clones, primers could be designed for PCR am plification of the microsatellite. This yielded 28 primer sets amplifying u nambiguously scorable products, of which 26 showed polymorphisms in a test set of six lettuce varieties. Practically all microsatellite-amplifying pri mer sets yielded products in lettuce's nearest relative, L. serriola, but o nly half of the primer sets yielded products in the more distant species L. saligna and L. virosa. An average polymorphism information content (PIC) v alue of 0.55 and an average number of 3.5 alleles per locus were in the nor mal range for a self-fertilizing species like lettuce. In addition, the inc idental cloning of a microsatellite-containing repeat family, apparently sp ecific for Lactuca, is reported and the implications for the efficient retr ieval of single-locus microsatellite sequences are discussed. The microsate llite loci isolated will be useful for distinguishing lettuce cultivars and for screening diversity of genetic resources.