Isolation, characterization, and inheritance of microsatellite loci in alpine larch and western larch

Microsatellite loci or simple sequence repeat loci (SSRs) were isolated in alpine larch (Larix lyallii Parl.) and western larch (Larix occidentalis Nutt.). In total, 14 SSR loci were characterized; two [(TCT)4, A7] came from published Larix DNA sequence data, one (CA)17 was obtained from a partial non-enriched alpine larch total genomic DNA library, and the remaining 11 loci were obtained from larch genomic DNAs enriched for (CA)n repeats. The SSR regions in these clones could be divided into three categories: perfect repeat sequences without interruption, imperfect repeat sequences with interruption(s), and compound repeat sequences with adjacent tandem simple dinucleotides. Eight of the 14 loci analyzed were found to be polymorphic and useful markers after silver-staining polyacrylamide gel electrophoresis. In addition, several SSR primers developed for alpine larch were able to successfully amplify polymorphic loci in its related species, western larch, and among other closely related taxa within the Larix genus. The inheritance of microsatellite loci was verified by analysis of haploid megagametophyte and diploid embryo tissues of progeny obtained from controlled crosses between western larch and alpine larch. All microsatellite loci analyzed had alleles that segregated according to expected Mendelian frequencies. Two species-specific markers (UAKLly10a and UAKLla1) allow easy and rapid identification of specific genetic entry of alpine larch and western larch at any stage in the sporophyte phase of the life cycle. Therefore, these markers are efficient in identifying the parental species and to validate controlled crosses between these two closely related species. These results are important in tree improvement programs of alpine larch and western larch aimed at producing genetically improved hybrid stock for reforestation in Western Canada and U.S.A.