RESTRICTION MAP AND POLYMORPHISMS OF NUCLEAR RIBOSOMAL GENES OF POPULUS-BALSAMIFERA

Balsam poplar (Populus balsamifera) clones from five populations, whic h were collected along a transect from northern Wisconsin to the north ern tree line, were evaluated for polymorphisms in nuclear ribosomal D NA. For this purpose, a restriction map was constructed using four six -cutter enzymes in single and double digests of genomic DNA. After ele ctrophoretic separation on agarose gets and Southern transfer, blots w ere hybridized to non-radioactively labeled heterologous rDNA probes o f soybean. Among populations, variation was detected in the length of the intergenic spacer between the tandem repeats of the coding regions and in the degree of methylation of one restriction enzyme recognitio n site. Based on a comparison of the derived restriction map of balsam poplar and other poplars, high homology was evident in the rDNA codin g regions among species, whereas the intergenic spacer varied slightly in both length and number of restriction sites.