IN SITU HYBRIDIZATION AND REPEATED DNA PROBES: USES IN THE ANALYSIS OF PHYLOGENY, ALIEN CHROMATIN AND SOMACLONAL VARIATION IN THE TRITICEAE (WHEAT, RYE HYBRIDS, AGROPYRON, CHROMOSOMES)

In situ hybridization using biotin-labeled DNA probes was performed on wheat, rye, wheat x rye hybrids, and several perennial species of the Triticeae. In this technique, hybridization sites were identified by the appearance of a brown color over blue (Giemsa-stained) chromosomes. Clones pSC 74 and pSC 119, which contain sequences from the 480-bp and 120-bp families of repeated DNA sequences in rye, were used as probes. In rye, the 480-bp sequence was clustered at 18 to 20 sites distributed over the seven chromosomes. The 120-bp sequence hybridized all over the seven rye chromosomes, giving them a distinct brown appearance. The 120-bp sequence also hybridized to eleven of the twenty-one wheat chromosomes, but only at a few distinct sites, producing a predominant blue color in wheat chromosomes. The distinguishable appearance between wheat and rye chromosomes produced by the 120-bp sequence allowed the efficient and sensitive detection of rye chromatin in wheat-rye chromosome translocations present in three wheat cultivars. In wheat x rye hybrids regenerated from tissue culture, amplification of 480-bp sequences was detected by the appearance of an enlarged hybridization site to pSC 74 at the short arm telomere of chromosome 7R. This same telomeric site appeared as an unlabeled, blue chromosome segment in an otherwise completely brown chromosome hybridizing entirely to the 120-bp sequence. Relationships among rye and eight perennial species were determined by homology to 120-bp and 480-bp sequences and similarity in situ hybridization patterns. The eight perennial species representing the genera Pseudoroegneria, Thinopyrum and Elymus hybridized with the 120-bp sequence, but only T. elongatum showed in situ hybridization patterns similar to those of rye. T. elongatum may therefore have affinity with rye. The rye-specific 480-bp sequence was present in the X genome of T. intermedium, suggesting a close relationship between the diploid X genome progenitor and rye. In situ hybridization patterns to the 120-bp sequence were similar among species with the same genomes, indicating the usefulness of the technique for determining genomic relationships.