Molecular Cytogenetic Analysis of Four Larix Species by Bicolor Fluorescence In Situ Hybridization and DAPI Banding

Mitotic metaphase complements of four Eurasian Larix species, L. gmelinii, L. principis-rupprechtii, L. kaempfeeri, and L. olgensis, were analyzed by bicolor fluorescence in situ hybridization (FISH) with 25S and 5S rDNA probes as well as DAPI banding. The four species were all diploids with the common chromosome number of 2n=24. All of the 25S rDNA clusters were located in the secondary constrictions of chromosomes, but the number of their sites varied among species. In L. kaempfeeri and L. olgensis, a pair of 25S rDNA loci were found on each of two large metacentric chromosome pairs, while in L. gmelinii and L. principisrupprechtii, another two loci were present on the long arms of one pair of submetacentric chromosomes. The 5S rDNA FISH pattern was less variable, with only one site commonly observed in each species. These loci occurred on a pair of large metacentrics that also harbored 25S rDNA on different arms. Bright, fluorescent DAPI bands were positioned adjacent to the centromeres of all but one chromosome pair of L. kaempfeeri and L. olgensis and adjacent to the centromeres of all but two chromosome pairs of L. gmelinii and L. principisrupprechtii. However, these bands showed obvious differences in intensity between the species, and together with the interspecific variation of 25S rDNA FISH patterns, they provide preliminary molecular cytogenetic evidence for phylogenetic study of these Larix species.