VARIATION IN THE NUCLEAR RIBOSOMAL DNA INTERNAL TRANSCRIBED SPACER (ITS) REGION OF PINUS-RZEDOWSKII REVEALED BY PCR-RFLP

In the genus Pious the internal transcribed spacers (ITS1 and ITS2) an d the 5.8s region of the nuclear ribosomal DNA are approximately 3000 bp in length. ITS1 is considerably longer than ITS2 and partial sequen ces of ITS1 indicate that this region is evolving rapidly and exhibits intraspecific variation. The ITS2 and 5.8s regions are relatively con served. We surveyed restriction fragment length variability of PCR-amp lified fragments (PCR-RFLP) of the ITS region in four populations (86 individuals) of Pinus rzedowskii, a pine endemic to western Michoacan, Mexico. Five of the restriction endonucleases assayed revealed variat ion, with a total of 13 variants, most of which were length mutations of 300-900 bp. A moderate degree of population differentiation was det ected. The average diversity (Shannon's index) of ITS fragment size pa tterns was 1.19, with 34% of the variation due to differences among po pulations and 66% due to differences among individuals within populati ons. The same individuals were assayed for nine polymorphic isozymes, which gave diversity measures similar to those of each restriction end onuclease.