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Bridging Ploidy Differences in Crested Wheatgrass with Hexaploid x Diploid Hybrids¹

Hybrids between hexaploid (2n = 6x = 42) and diploid (2n = 2x = 14) Agropyron cristatum (L.) Gaertn. were crossed with the 6x and 2x parents, with colchicine-induced tetrapinid (C4x) A. cristatum (2n = 4x = 28), and with natural tetraploid (N4x) A. desertorum (Fisch. ex. Link) Schult. (2n = 4x = 28). Fertility and chromosomepairing relationships were studied in the triploid, tetraploid, and pentaploid progenies to evaluate ways that 6x- 2x hybrids could be used to combine the genetic resources of the three ploidy levels into one germplasm pool. Cytological data demonstrated that genomes from e three ploidy levels were similar, differing only by structural rearrangements. The (6x-2x) x C4x tetraploids were the most fertile hybrids, with an average seed set of 53 seeds per spike compared with 21, 9, and 0.2 seeds per spike for the (6x-2x) x N4x, (6x-2x) x 6x, and (6x-2x) x 2x hybrids, respectively. Some (6x-2x) x N4x hybrid tetraploids, with germplasm of all three ploidy levels represented, were fertile enough to be used directly in a breeding program. The (6x-2x) x C4x hybrid tetraploids should have merit in crosses with (6x-2x) x N4x hybrids and N4x tetraploids to produce breeding populations with germplasm from the three ploidy levels. The sterility and meiotic irregularity of the (6x-2x) x triploid hybrids and (6x-2x) x 6x pentaploid hybrids seriously limit their direct use in breeding schemes.

Key Words: Agropyron cristatum • Agropyron desertorum • Polyploidy • Autopolyploidy • Interspecific hybridization • Sterility • Grass breeding • Cytogenetics Introgression

² Research geneticists, SEA-AR-USDA.

Received for publication January 18, 1979.

This article has been cited by other articles:

				K. B. Jensen, S. R. Larson, B. L. Waldron, and K. H. Asay Cytogenetic and Molecular Characterization of Hybrids between 6x, 4x, and 2x Ploidy Levels in Crested Wheatgrass Crop Sci., December 2, 2005; 46(1): 105 - 112. [Abstract] [Full Text] [PDF]