VARIATION AND INHERITANCE OF RIBOSOMAL DNA IN PINUS-SYLVESTRIS L (SCOTS PINE)

Variability in the ribosomal DNA (rDNA) gene family was surveyed in Scots pine (Pinus sylvestris L.) populations from southern and northern Finland. A total of 97 trees were studied with three restriction enzymes, revealing 13 variable rDNA phenotypes. Each rDNA phenotype represents the combined genotype of the eight rDNA loci (NORs, nucleolus organizer regions) that are present in the Scots pine genome. The studied Scots pine populations were equally variable and there was no evidence of geographic differentiation. Of the total rDNA diversity of the species, 86 per cent was found within populations (including within-individual variability) and 14 per cent was found between populations. Within individual trees, one to four rDNA repeat types were distinguished. No variation was found in the coding regions but variable restriction sites were identified in the IGS and transcribed spacer regions. The inheritance pattern of an rDNA variant carrying a 0.4 kb deletion in the transcribed spacer region was studied. The deletion-carrying rDNA variants were distributed non-randomly across the NOR loci and showed regular Mendelian segregation in the progeny. The observed distribution pattern of rDNA variability suggests that the rate of intrachromosomal homogenization is greater than that of interchromosomal homogenization in Scots pine.