ASSESSMENT OF REPETITIVE DNA VARIATION AMONG ACCESSIONS OF HEXAPLOID AND TETRAPLOID WHEAT

Genetic evidence has suggested that only a few coding genes separate varietal groups within the wheat species Triticum aestivum L. emend. Thell and T. turgidum L. emend. Morris & Sears. However, reduced chromosome pairing is often observed in wheat intraspecific hybrids. Most of the DNA in higher plants is noncoding repetitive DNA, and this type of DNA has been hypothesized to influence chromosome pairing. Our objective was to determine whether this genomic component varies among wheat accessions. Thus, we cloned representatives of six repetitive DNA families found primarily in the wheat A or B genomes. These cloned sequences were used to address the possibility of variation for either restriction fragments or sequence abundance among a diverse set of wheat germplasm. Southern blot analysis of genomic DNA from 33 accessions digested with eight restriction enzymes revealed no restriction site variation for any of the six repetitive sequences. This suggests a lack of sequence divergence for the repetitive DNA families among the accessions. However, dot blot analysis showed that one B genome sequence varied significantly (P < 0.01) in copy number among 10 diverse accessions of T. aestivum. These results suggest that copy number variation for repetitive DNA families may exist among accessions of wheat, although sequences of the families as indicated by restriction fragment analysis are conserved.