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Hybrids Between Tetraploid and Hexaploid Crested Wheatgrasses¹

Doubled-diploid Agropyron cristatum (L.) Gaertn., 2n=28, and tetraploid A. desertorum (Fisch. ex Link) Schult., 2n=28, hybridized with hexaploid A. cristatum, 2n=42. Meiosis in the parent plants was typical of that in autoploids. Pentavalent associations, up to five per cell, in the 35-chromosome hybrids indicated close homologies between parental genomes. Occasional higher multivalent associations and bridge-fragment formations at anaphase I indicated some structural heterozygosity.

All crested wheatgrasses—whether diploid, tetraploid, or hexaploid—apparently contain one basic genome that has undergone some structural rearrangements. It is recommended that crested wheatgrasses be regarded as one species with taxonomic differentiation at the subspecies and varietal levels.

The pentaploid hybrids were surprisingly fertile and ranged from 0.54 to 4.32 seeds per spikelet under open pollination. Some hybrids were considerably more vigorous than either parent and may have value in a breeding program. Interploidy hybridization is recommended to crested wheatgrass breeders.

Key Words: Agropyron cristatum • Agropyron desertorum • Genome analysis • Autopolyploidy

² Research Geneticist, Crops Research Division, Agricultural Research Service, U. S. Department of Agriculture.

Received for publication May 12, 1969.