DIFFERENTIATION OF THE SY GENOMES IN ASIATIC ELYMUS

There are approximately forty tetraploid Elymus species containing the "SY" genomes, which all occur in Asia. This group of species are traditionally classified into four different sections, viz., Sect. Elymus L., Sect. Goulardia (Huston) Tzvelev, Sect. Clinelymiopsis (Nevski) Tzvelev and Sect. Anthosachne (Steud.) Tzvelev. This treatment reflects the large morphological variation of the group. A meiotic pairing study of interspecific hybrids between 27 Elymus taxa possessing "SY" genomes, representing the four sections, and covering the whole geographic distribution area of the group, demonstrated a pattern of genomic relationships which differs from the traditional taxonomic system based on morphology. The differentiation of the "SY" genomes in these species is obvious and in accordance with their geographic origin instead of their morphological similarity. Species from the same region, i.e., within Eastern Asia, North Central Asia, South Central Asia, or Western Asia, have generally high genomic affinity to each other, whereas species from the different regions show comparatively lower genomic affinity. There is a clear tendency that the degree of genomic affinity between the species is gradually decreasing with increasing geographic distance of their origins.