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Cytogenetics of Crested Wheatgrass Triploids¹

Meiosis and fertility were studied in triploids derived from diploid Agropyron cristatum, 2n=14; tetraploid A. desertorum, 2n=28; and A. cristatum x A. desertorum crosses. Chromosome associations in autotriploid A. cristatum averaged 4.39 I. 4.51 II, and 2.53 III in 278 meta phase-I cells. Trivalent associations were less common in autotriploid A. cristatum than in other known Gramineae autotriploids. Triploid A. desertorum averaged 3.88 I, 4.20 II, and 2.91 III in 116 cells at metaphase I. The A. desertorum genomes appeared to be essentially homologous except for a possible inverted segment in one chromosome and cryptic structural differences. The A. cristatum x A. desertorum triploid averaged 2.43 I, 3.50 II, 3.10 III, 0.53 IV, and 0.03 V in 70 metaphase-I cells. The A. cristatum and A. desertorum genomes apparently differ from one another by several structural chromosome rearrangements including interchanges and inversions.

Diploid A. cristatum, triploid A. cristatum, tetraploid A. desertorum, triploid A. desertorum, and A. cristatum x A. desertorum triploids were represented by genome formulas of CC, CCC, C₁C₁C₁C₁, C₁C₁C₁ and C₁C₁C₁, respectively. Although A. desertorum is an apparent autotetraploid, it appears doubtful that it originated directly from the only known form of diploid A. cristatum.

Although A. cristatum and A. desertorum differ in ploidy level and morphology, they contain the same basic genome and do not appear to be distinctly different species. It is suggested that A. desertorum and all other crested wheatgrass be designated as subspecies and varieties of A. cristatum. Grass breeders are advised to consider all crested wheatgrasses, regardless of ploidy level, as a single breeding population.

Key Words: Agropyron • cytology • cytotaxonomy • genome • polyploidy

² Research Geneticist, Crops Research Division, ARS, USDA, and Assistant Professor of Biology, California State Polytechnic College, San Luis Obispo, (formerly Graduate Assistant, Utah State University).

Received for publication January 27, 1967.

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