Morphological, Cytological, and Taxonomic Relationships Between Agropyron repens and A. Elongatiforme (Gramineae)

Abstract

Sixty-nine collections of Agropyron elongatiforme Drob. and A. repens (L.) Beauv. were made in Iran in 1972. Differentiating the two species was difficult in the field because of close morphological similarities. The collections were subse- quently grown at a common location near Logan, Utah, where their morphological and cytological characteristics were observed. No single morphological character can always be used to separate A. elongatiforme from A. repens. However, separations are easily made when the following characters are considered together: presence or absence of pubescence, awns vs. awnlessness, spikelet shape, plant color, and abun- dance or scarcity of culms. Chromosome number is a sure means of distinguishing between the two species; A. repens is hexaploid (2n = 42) and A. elongatiforme is octoploid or near-octoploid (2n = 52 to 56). A hybrid between A. repens and A. elongatiforme was morphologically intermediate to the parents. The hybrid had 49 chromosomes and averaged 8.03 I, 19.41 II, 0.37 III, 0.22 IV, and 0.03 V in 168 metaphase-I cells. Pairing relationships indicate that A. elongatiforme has the same chromosomes as A. repens plus an additional genome. Genome formulas of SSS2S2XX, S,S,S2S.XXYY, and S,S,S2S2XXY are proposed for A. repens, A. elon- gatiforme, and the F1 hybrid, respectively. The hybrid produced 75% stainable pollen and averaged 10.4 seeds per spike. Because of close morphological affinities, three genomes in common, and free gene exchange, A. elongatiforme is treated as A. re- pens subsp. elongatiforme (Drob.) D. R. Dewey. Most botanists, agriculturists, and even many lay people in temperate regions are acquainted with Agropyron repens (L.) Beauv. (quackgrass) because of its wide distribution and its weedy characteristics; it is prob- ably the world's most widespread noxious weed. However, few are ac- quainted with Agropyron elongatiforme Drob., a taxon that has a close mor- phological affinity to A. repens but with a much more restricted