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

Variability in the ribosomal DNA (rDNA) gene family was surveyed in Sc ots pine (Pinus sylvestris L.) populations from southern and northern Finland. A total of 97 trees were studied with three restriction enzym es, revealing 13 variable rDNA phenotypes. Each rDNA phenotype represe nts the combined genotype of the eight rDNA loci (NORs, nucleolus orga nizer 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 spe cies, 86 per cent was found within populations (including within-indiv idual variability) and 14 per cent was found between populations. With in 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 t he transcribed spacer region was studied. The deletion-carrying rDNA v ariants were distributed non-randomly across the NOR loci and showed r egular Mendelian segregation in the progeny. The observed distribution pattern of rDNA variability suggests that the rate of intrachromosoma l homogenization is greater than that of interchromosomal homogenizati on in Scots pine.