VARIATION OF MOLECULAR MARKERS AMONG GEOGRAPHICALLY DIVERSE ACCESSIONS OF TRITICUM-TAUSCHII

Triticum tauschii (Coss.) Schmal. (genome DD), a diploid progenitor of hexaploid wheat (Triticum aestivum L.; AABBDD), grows across large areas of southwest Asia and contains more genetic variability for disease and insect resistance, isozymes, and seed storage proteins than the D genome of T. aestivum. To study patterns of variability at a large number of loci, we determined restriction fragment length polymorphism genotypes at 25 loci in a germ-plasm collection of 102 T. tauschii accessions. All accessions were homozygous at all loci, so "alleles" and "genotypes" were equivalent. Twenty loci were polymorphic, with two to six genotypes per locus and polymorphic indexes ranging from 0.06 to 0.74. Linkage disequilibrium was widespread. On the basis of Hedrick's probability of genotypic identity, botanical varieties T. t. ssp. eusquarrosa var. typica and T. t. ssp. eusquarrosa var. anathera were very similar to each other, as were T. t. ssp. strangulata and T. t. ssp. eusquarrosa var. meyeri, with a large genetic distance between these two pairs of taxonomic groups. Genetic variability for molecular markers was highest near the Caspian Sea, intermediate in Afghanistan, and lowest in Turkey and Pakistan. Genetic and geographical distances were related and generally consistent with the hypothesis that T. tauschii originated near the southern or southwestern coast of the Caspian Sea. Unique genotypes were found in most regions. The results of this study, along with data on economically relevant traits, will provide a basis for selecting breeding parents from the T. tauschii germ-plasm collection.