Wheat taxonomy and cultivar identification using molecular markers

Molecular markers were used in an attempt to determine the phylogenetic relationships of hexaploid wheats within Triticum aestivum L. and to identify wheat cultivars. Random amplified polymorphic DNA (RAPD), restriction fragment length polymorphism (RFLP), gliadin protein and cytological analyses were used to assess phylogenetic relationships among five morphological groups of hexaploid wheat, namely, macha, common wheat, spelta, vavilovii and semi-wild wheat (SWW). RAPD and gliadin data were analysed using the NTSYS-pc computer program to generate Jaccard genetic similarity coefficients. Coefficients of genetic similarity in the cytological study were calculated based on the number of chiasmata in hybrids. Dendrograms were constructed based on these coefficients. The dendrogram based on RAPD analysis grouped 15 accessions into five distinct clusters which were in agreement with the morphology-based classification. The results indicated that common wheat was closely related to vavilovii. Spelta was less related to the common and vavilovii wheat cluster. SWW was distantly related to common wheat. Macha was the least related to the previous clusters. These results were consistent with those based on cytological analysis. The results of gliadin analysis were not completely consistent with those based on RAPD and cytological analyses. RFLP data showed that it was difficult to determine phylogenetic relationships among the five groups of hexaploid wheat based on variation in the intergenic spacer region of the 18-25S rRNA unit. Polymerase chain reaction analysis of the 5S rRNA unit and the internal transcribed spacer of the 18-25S rRNA unit did not show any polymorphism among and within the five groups of hexaploid wheat. Twelve mis-classified Triticum accessions were found in macha and vavilovii wheat collections and investigated using RAPD and cytological analyses. A dendrogram based on RAPD analysis classified the 12 accessions into either T. monococcum, T. turgidum spp. dicoccum or T. timopheevii. The results were in agreement with cytogenetic data and morphological observations. The genetic diversity of spelta and macha wheat was also investigated using RAPD analysis and the results were generally consistent with geographic origins. Macha wheat germplasm was found slightly more diverse than spelta wheat although macha has a restricted geographic origin. In addition, duplicate accessions of macha and spelta were identified based on RAPD analysis.; In the study of wheat cultivar identification and pedigree assessment, 29 cultivars were investigated using RAPD analysis. Cultivar specific markers were found, and at least eight cultivars could be identified using these specific markers. Cultivar relationships based on genetic similarity values were consistent with known pedigrees. The study demonstrated that RAPD analysis can be used for estimating the phylogenetic relationships among the five groups of hexaploid wheat, reclassifying misclassified wheat germplasm, surveying the genetic diversity of spelta and macha wheat and identifying common wheat cultivars and duplicated accessions in wheat germplasm collections.