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Derivation of a New Forage Grass from Agropyron repens ‘ Agropyron spicatum Hybrids¹

Pentaplold hybrids (2n=35) of Agropyron repens (L.) Beauv. (2n=42) x Agropyron spicatum (Pursh) Scribn. & Smith (2n=28) were intercrossed, backcrossed to both parent species, and open-pollinated. The hybrid derivatives differed widely in vigor, rhizome development, spike characteristics, and fertility. Vigor, meiotic regularity, and fertility improved rapidly in advanced generations. By the F₅ generation, the hybrid population was largely hexaploid (2n=42), and some plants had achieved complete meiotic stability and full fertility. Almost one-fourth of the F₅'s were nonrhizomatous, and about half had only short rhizomes. Chromosome pairing in the various hybrid populations indicated that A. repens and A. spicatum have considerable genomic homologies. Genome formulas for A. repens and A. spicatum were written as S₁S₁S₂S₂XX and SSSS, respectively. Introgression via genetic exchange between the S genomes of A. repens and A. spicatum made possible the derivation of fertile hybrid progenies with morphological characteristics of both species. The advanced-generation hybrids appear to have potential as economically important forage grasses.

Key Words: Quackgrass • Bluebunch wheatgrass • Introgression • Grass breeding • Genome analysis

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

Received for publication September 2, 1975.