Intergenic spacer length variability in cultivated, weedy and wild rye species

Non-coding rDNA spacers (IGS) can vary substantially in size due to differences in the number of repetitive elements among closely related species. Three pairs of universal primers were used in this study for the amplification of non-coding regions of ribosomal (rRNA) IGS. The amplified IGS products obtained from 19 Secale accessions, which included both cultivated and noncultivated rye and which represented three species and four subspecies of the genus Secale, showed a high level of polymorphism. The PCR results were characterized by multiple bands (1-6), different sizes (750bp-3250bp) and 100% polymorphism. Cluster analysis using the neighborjoining method based on the Dice’s coefficient of genetic similarity showed a division of the studied species into two similarity groups. All the studied Secale cereale ssp. cereale were found to belong to the same similarity group. The variation in the size of the IGS among the species which was detected in this study could be due to dissimilarity between the sequences of their respective repetitive elements or between their tandem repeat numbers. The highly interspecific polymorphisms for the rDNA IGS regions suggested that IGS might be a useful molecular marker in studies of Secale species.