Cytological characterization of heterochromatin and rDNA in Pinus radiata and P-taeda

Fluorochrome C-banding of Pinus radiata and P. taeda metaphase chromosomes showed many pericentromeric DAPI bands and interstitial CMA bands in P. rad iata, and centromeric and interstitial CMA bands in P. taeda. Giemsa C-band patterns differed between the species with centromeric bands in P. radiata but no consistent bands in P, taeda. A karyotype of P. radiata was develop ed based on banding patterns that distinguished all but two of the 12 pairs of chromosomes. Insitu hybridization (ISH) using probes for high-copy ribo somal DNA (rDNA) showed 10 pairs of 18S-25S sites and two pairs of 5S sites in both species. Most of the sites were interstitial or centromeric.