Elimination of a tandem repeat of telomeric heterochromatin during the evolution of wheat

An analysis of accessions of Triticum and Aegilops species (86 diploid, 91 tetraploid and 109 hexaploid) was performed using squash-dot hybridization with the tandem repeat Spelt1 sequence as a probe. The Spelt1 sequence is a highly species-specific repeal associated with the telomeric heterochromat in of Aegilops speltoides Boiss. in which its copy numbers vary from 1.5 x 10(5) to 5.3 x 10(5). The amounts of Spelt1 are sharply decreased in tetrap loid and hexaploid species and vary widely from less than 10(2) to 1.2 x 10 (4). Two tetraploid wheats, Triticum timopheevii Zhuk. and T. carthlicum Ne vski, are exceptional endemic species and within their restricted geographi cal distributions maintain the amounts of Spelt1 unaltered. The Spelt1 repe titive sequence was localized on the 6BL chromosome of tetraploid wheat Tri ticum durum Desf. cv 'Langdon' by dot-hybridization using D-genome disomic substitution lines. The possible causes of the loss of the telomere-associa ted tandem repeat Spelt1 in the process of wheat evolution and polyploidiza tion are discussed.