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Morphology, Cytology, and Fertility of F₁ and Induced-amphiploid Hybrids of Elymus canadensis — Agropyron subsecundum¹

Octoploid (2n=56) amphiploids of Elymus canadensis L. x Agropyron subsecundum (Link.) Hitchc. were obtained by treating sterile tetraploid (2n=28) F₁ hybrids with colchicine. Chromosome doubling initially restored fertility but drastically reduced vegetative vigor. Dry matter yields of the amphiploids in the C₂ to C₅ generations were about 50% of those of the F_l's. The range in chromosome number changed from 2n=54 to 58 in the C₁ to 2n=27 to 59 in the C₅ generation, while the population means decreased from 2n=55.9 to 2n=53.8. Meiotic irregularities tended to increase in each succeeding amphiploid generation. Fertility declined from 2.36 seeds per spikelet in the Co generation to 0.78, 0.58, 0.50, 0.37, and 0.22 in the C₁ to C₅ generations, respectively. Amphiploid sterility was attributed to heterogenetic pairing between the closely related E. canadensis and A. subsecundum chromosomes. Chances of synthesizing a fertile, cytologically stable octoploid species from E. canadensis x A. subsecundum amphiploids, or from amphiploids with a similar genome constitution, are remote.

Key Words: Intergeneric hybridization • Canada wildrye • Bearded wheatgrass • Speciation • Colchicine • Polyploidy • Genome analysis

² Research geneticist, ARS-USDA, Logan, UT 84322.

Received for publication May 12, 1976.