Cytogenetics, Mode of Pollination, and Genome Structure of Agropyron mutabile

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Abstract
A. mutabile Drob. s.l., a perennial caespitose forage grass species complex, occurs in northern Europe and Asia and in the mountains of Central Asia. Ten plants from 1 collection (P.I. 314622) from the Tien Shan Mountains east of Alma Ata, Kazakhstan, USSR, were evaluated for chromosome number, meiotic behavior and mode of pollination. All plants were fully self-fertile, and they behaved meiotically as allotetraploids (2n = 28). Hybrids were obtained between A. mutabile and 4 spp. with known genome constitutions: A. libanoticum Hack., a Middle Eastern SS diploid (2n = 14); A. caninum (L.) Beauv., an Asian SSHH tetraploid (2n = 28); A. dasystachyum (Hook.) Scribn., a North American SSHH tetraploid (2n = 28); and Sitanion hystrix, a North American SSHH tetraploid (2n = 28). Chromosome pairing in the A. libanoticum .times. A. mutabile hybrids (2n = 21) indicates that the 2 spp. share a common but not identical genome.sbd.SS. Pairing in the tetraploid hybrids shows that A. mutabile is a SSHH species with a very close genomic affinity to A. caninum. The A. mutabile .times. A. caninum hybrids were slightly fertile; all others were completely sterile. Although A. mutabile and A. caninum are closely related, they are easily distinguished morphologically, and barriers to genetic exchange are high. Consequently, they warrant retention as separate species.