Cytogenetic and Taxonomic Relationships among Three Diploid Crested Wheatgrasses1

Abstract

Until recently, only one diploid (2n= 14) taxon of crested wheatgrass [Agropyron cristatum (L.) Gaertn.] was recognized. This diploid, ‘Fairway’, differs morphologically from two diploid plant introductions, PI 229574 from Iran and PI 314600 from the USSR. The purposes of this study were to: (1) define the genomic relationships among the three diploid taxa, (2) determine if restrictions to gene flow occur among the diploids, and (3) examine the taxonomic implications of the data.The diploid taxa were hybridized with relative ease and produced F1 hybrids that were morphologically intermediate to their parents. Mean chromosome pairing at Metaphase I in the three hybrid combinations ranged from 1.38 to 2.25I, 5.05 to 5.83II, 0.03 to 0.52III, and 0.005 to 0.18IV. The pairing data demonstrate that the diploids contain the same basic genome, but their genomes differ by structural rearrangements of some chromosomes. Stainable pollen averaged 19.3 to 24.6% and seed set averaged 0.25 to 0.58 seeds per spike in the three hybrid combinations. The moderately high sterility in the hybrids serves as a genetic barrier but does not preclude gene flow among the diploids.The three diploid taxa are correctly identified as A. cristatum, but they should be separated at the subspecies level. We think that PI 229574 belongs to A. cristatum subsp. cristatum. However, subspecies designations for Fairway and PI 314600 must be deferred until more information is accumulated.