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Hybrids Between Diploid and Hexaploid Crested Wheatgrass¹

Thirty-seven unemasculated spikes of hexaploid Agropyron cristatum (L.) Gaertn., 2n=42, pollinated by diploid A. cristatum, 2n=14, yielded seven tetraploid hybrids, 2n=27-29. The reciprocal cross was unsuccessful. The hybrids were morphologically intermediate between the parent plants, but they had a closer overall resemblance to the hexaploid. Chromosome pairing was almost complete in the 28-chromosome hybrids which averaged 0.40^I, 7.51^II, 0.41^III, 1.07^IV 0.22^V, 0.18^VI, 0.01^VII, 0.31^VIII, 0.04^IX, 0.09^X, and 0.09^XII in 72 metaphase-I cells. Multivalent associations were attributed to a combination of heterozygous interchanges and autoploidy. The genomes of diploid and hexaploid A. cristatum are homologous except for structural rearrangements, primarily interchanged chromosome segments. Three 28-chromosome hybrids produced 35 to 75% stainable pollen and averaged 11.2, 12.8, and 20.9 seeds per spike under open pollination. The hybrids averaged 9.4 and 10.1 seeds per spike when pollinated by A. desertorum (Fisch. ex Link) Schult., 2n=28, and induced-tetraploid A. cristatum, 2n=28, respectively. The gene pools of diploid, tetraploid, and hexaploid crested wheatgrass can be merged into a single breeding population at the tetraploid level. This approach is recommended to crested wheatgrass breeders.

Key Words: Agropyron cristatum • Grass breeding • Polyploidy

² Research Geneticist, ARS, USDA, Logan, Utah 84322.

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