LENGTH POLYMORPHISM IN THE RIBOSOMAL DNA INTERGENIC SPACER OF RYE ANDSLENDER WILD OATS

Variation in ribosomal DNA spacer length was analyzed in nine populati ons of three species of grasses by restriction fragment length polymor phism analysis using non radioactive labeling. Three populations of ry e. Secale cereale, four of the tetraploid slender wild oat, Avena barb ata, and two of its diploid ancestor A. hirtula were analyzed. Extensi ve spacer length polymer phism, attributed to the differences in numbe r of spacer subrepeats within rDNA arrays, existed in the three specie s. The fragment lengths generated by EcoRI in the two oat species rang ed from 2.2 to 3.2 kb, while the fragments generated by BamHI in rye r anged from 4.7 to 6.2 kb. The phenotypic variability observed agrees w ith the expectations from the different mating types and number of rDN A loci of these three species. In the two oats species, the most frequ ent spacer length variants were shared for both oat species and were p resent in all the populations; likewise, frequent spacer length varian ts were present in the three rye populations. The results are compared with previous data on rDNA polymorphism in rye and in slender oats po pulations and on genetic variability for isozyme loci in the same popu lations of both oats and rye.