SURVEY OF MICROSATELLITE DNA IN PINE

A large insert genomic library from eastern white pine (Pinus strobus) was probed for the microsatellite motifs (AC)(n) and (AG)(n), all 10 trinucleotide motifs, and 22 of the 33 possible tetranucleotide motifs . For comparison with a species from a different subgenus, a loblolly pine (Pinus taeda) genomic library was also probed with the same set o f di- and tri-nucleotide repeats and 11 of the tetranucleotide repeats . The four most abundant microsatellite motifs in both species were (A C)(n), (AG)(n), (AAT)(n), and (ATC)(n), which as a group accounted for over half the microsatellite sites investigated. The two dinucleotide repeats were the most abundant microsatellite motifs tested in both s pecies, each at 2-4.5 sites/megabase pair (Mbp), but the two trinucleo tide motifs were nearly as abundant and are considered good candidates for pine microsatellite marker development efforts. Eastern white pin e had more than twice as many (AC)(n) as (AG)(n) loci, in contrast wit h loblolly pine and most other plant species in which (AG)(n) is more abundant. In both pine species the minimum estimated genome density fo r all microsatellites, excluding (AT)(n) repeats, was 16 sites/Mbp.