Genetic studies of five white pine species and their interspecific hybrids by isozymes

Abstract

The genetic structure, linkage relationships and genetic variation of Pinus strobus, P. monticola, P. griffithii, P. peuce and~. koraiensis were investigated by isozyme analysis, using starch gel electrophoresis, based on tissue from mature needles and megagametophytes. The possibility of using isozyme analysis for identification of these species and their interspecific hybrids was also investigated. Thirteen enzyme systems were analyzed, most of which were shown to be under multiple gene control. Thirty-six loci coded for the 13 enzyme systems in each of the species. Inheritance studies showed that most of the isozyme variants were under Mendelian single-gene control. Determination of linkage relationships among the 36 gene loci revealed up to three linkage blocks in each species. The gene arrangement had common relationships for all species. Generally, one block consisted of LAP2 and MDH3, the second of IDH and AC02, and the third of MDH2 and LAP 3 . Further ii observations indicated that most of these linked genes were on the same chromosome. These results are discussed in terms of the conservative nature of the pine genome and its evolution. Their practical uses are noted. Substantial genetic variation was evidenced in all the species. Based on 8 enzyme systems and 14 isozyme loci, the mean values of average heterozygosity, proportion of polymorphic loci, and number of alleles per locus were: P. strobus - 0.226, 50.0, and 2.5; P. monticola - 0.233, 78.6 and 2.3; P. griffithii - 0.190, 57.1 and 2.1, P. peuce - 0.152, 71.4 and 2.6; and P. koraiensis 0.134, 50.0 and 2.1 respectively. These values are comparable to most other conifer species. Genetic similarities and distances, divergence times based on allele frequencies and other results from a cluster analysis showed that P. strobus, P. monticola and P. griffithii were genetically the closest species while P. peuce and P. koraiensis each formed a separate cluster. The results are discussed in view of the evolution and conservative nature of these pines and subsections Cembrae and Strobi. Several alleles were ~dentified as markers for P strobus, P. monticola, P. griffithii, P. peuce and P. koraiensis and their interspecific hybrids. The practical and taxonomic importance of these marker allozymes is discussed.