Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 15, 1999
Publication Date: N/A
Interpretive Summary: Western wheatgrass is an important rangeland plant for livestock grazing in much of temperate North America. However, native Great Basin plants produce little forage, which often causes animals to decline consumption. Production is typically low-growing because of an excessive degree of spread by underground stems called rhizomes. Western wheatgrass is also poor in seed production, germination, and seedling vigor. Western wheatgrass is believed to have descended from hybrids of two other rhizome-bearing species, thickspike wheatgrass and beardless wildrye. A gene present in DNA found in the leaf chloroplasts, cell structures where photosynthesis occurs, was analyzed in these three grasses and other related species. The DNA sequences for each serve as fingerprints for genotype. This analysis determined that the "mother" of western wheatgrass was thickspike wheatgrass and the "father" was beardless wildrye. Establishing this parentage is important for "reconstruction" of a new western wheatgrass that is adapted to the Great Basin but does not have the poor forage production, seed production, germination, and seedling vigor of the natural western wheatgrass. This is indeed possible because close relatives of thickspike wheatgrass, i.e., Snake River wheatgrass, and beardless wildrye, i.e., basin wildrye, have the desired characteristics lacking in naturally occurring western wheatgrass.
Technical Abstract: We compared the DNA sequences of a 762-base pair (bp) segment of the ndhF chloroplast gene of western wheatgrass (Pascopyrum smithii) with that of its putative allotetraploid (Elymus, Leymus) and diploid (Pseudoroegneria, Hordeum, Psathyrostachys) ancestors, as determined from genome analysis. To ascertain the 2x to 8x chloroplast phylogeny, the gene sequences were aligned and a phylogenetic tree was constructed by the neighbor-joining method. Pascopyrum smithii differed by 0 to 2 and 6 to 9 bp from its two 4x ancestors, Elymus and Leymus. Elymus differed by 2 and 10 to 13 bp from its two 2x ancestors, Pseudoroegneria and Hordeum, respectively. Pascopyrum, Elymus, and Pseudoroegneria taxa clustered together, but separately from Leymus and Hordeum taxa. The Pascopyrum chloroplast genome appears to be inherited from the diploid Pseudoroegneria through the tetraploid Elymus. A true compatibility between the nuclear content of the polyploids and the Pseudoroegneria cytoplasm appears to account for its presence in Elymus and Pascopyrum. De novo synthesis of Pascopyrum germplasm from its tetraploid ancestors should be conducted with cognizance of the preference for Pseudoroegneria cytoplasm found in nature. Leymus differed from Psathyrostachys by 14 to 15 bp, indicating the second unknown diploid ancestor of Leymus may have contributed its chloroplast DNA. Revised genomic designations for Pascopyrum smithii and Elymus lanceolatus are StHNsXm and StH, respectively, where the underline indicates the genome of cytoplasmic origin.