Development of Triticum Taxonomy

Over the past 20 years, the development of cytology, genetics, and crossbreeding has accumulated abundant objective data and documents for wheat, one of the most important crops in the world. New knowledge is helpful for understanding phylogeny of wheat. Correspondingly, some questions challenged the old concept of wheat taxonomy. For instance, the generally accepted six species including commercial cultivars in dinkel reihe can easily hybridize each other and their hybrids usually had normal chromosome pairing and high fertility. The morphological difference used as a key trait of species classification can be caused by a single gene. Such as for the spike shape of T. aestivum and T. spelta, there is only the gene difference between Q and q. The difference between T. compactum and other species is only caused by the gene c, while the difference between T. sphaerococcum and T. aestivum is due to the gene S (Ellerton 1939; McGee 1958). Therefore, many scholars disagreed the treatment of six “species.” They thought that T. aestivum, T. spelta, T. compactum, T. macha, T. vavilovii, and T. sphaerococcum belong to a same species. Thellung (1918), McGee (1954), and Sears (1956a, b) regard them as subspecies of T. aestivum, as following: