Characteristics of single- and multi-copy microsatellites from Pinus radiata

Dinucleotide microsatellites were isolated from Pinus radiata using both a standard genomic library and libraries enriched for microsatellites. Locus-specific primers were designed to amplify 43 unique microsatellites. Thirty two of these loci had interpretable PCR patterns, II of which were polymorphic in a screen of 19 P. radiata individuals; all 11 polymorphic loci contained at least 17 repeats in the sequenced plasmid. Six of the eleven primer pairs amplified multiple fragments per individual (3-8), suggesting that these loci were present in multiple copies in the genome. Genotyping a 48-tree P. radiata production population with seven of the most polymorphic microsatellites revealed an average of 17 bands per locus (the multi-copy microsatellites were treated as one locus). When tested on known pedigrees, both single and multi-copy microsatellites exhibited codominant inheritance and Mendelian segregation. Two loci had null alleles and one locus had a high frequency of non-parental alleles, suggesting a high mutation rate. Eight of these microsatellites, including five multi-copy loci, were placed on a partially constructed P. radiata genetic map. Four of the five multi-copy microsatellites had two or more sets of alleles that mapped to the same locus, and the fifth mapped to two unlinked loci. All seven tested primer pairs amplified PCR products from other species of hard pine, three amplified products from soft-pine species, and one amplified bands in other conifers.