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

Variation in ribosomal DNA spacer length was analyzed in nine populations of three species of grasses by restriction fragment length polymorphism analysis using non radioactive labeling. Three populations of rye. Secale cereale, four of the tetraploid slender wild oat, Avena barbata, and two of its diploid ancestor A. hirtula were analyzed. Extensive spacer length polymer phism, attributed to the differences in number of spacer subrepeats within rDNA arrays, existed in the three species. The fragment lengths generated by EcoRI in the two oat species ranged from 2.2 to 3.2 kb, while the fragments generated by BamHI in rye ranged from 4.7 to 6.2 kb. The phenotypic variability observed agrees with the expectations from the different mating types and number of rDNA loci of these three species. In the two oats species, the most frequent spacer length variants were shared for both oat species and were present in all the populations; likewise, frequent spacer length variants were present in the three rye populations. The results are compared with previous data on rDNA polymorphism in rye and in slender oats populations and on genetic variability for isozyme loci in the same populations of both oats and rye.