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Poor seedling vigor limits the use of Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski] for complementary pasture. Tetraploid (2n=4x=28) plants of Russian wildrye have greater seedling vigor in greenhouse studies when compared to plants with the normal diploid chromosome complement (2n=2x=14). Objectives of this research were (i) to compare seedling emergence and development of diploid and tetraploid Russian wildrye in solid-seeded, single-row field plots and (ii) to document early seedling development and morphology in a controlled environment chamber. Seed mass averaged 2.70 mg seed(-1) for diploids and 4.66 mg seed(-1) for tetraploids. Initial seedling emergence averaged approximately 33% greater for tetraploids than diploids for both early and late field planting dates. Tiller number averaged only slightly, and generally not significantly, greater for diploids than tetraploids (maximum difference of 0.3 tillers plant(-1)) in solid-seeded rows in the field. Seedling height was consistently greater for tetraploids than diploids, a result of greater leaf length. Larger leaf size did not result in fewer leaves or in slower leaf development for tetraploids. Seedling emergence from a 63 mm depth in a controlled environment chamber averaged 46% for tetraploids and 10% for diploids at a 16/13 degrees C diurnal temperature regime and 11 and 6%, respectively, for tetraploids and diploids at a 23/18 degrees C temperature regime. Coleoptile length averaged 61 mm for tetraploids and 49 mm for diploids at the 16/13 degrees C temperature regime and 42 and 43 mm for tetraploids and diploids, respectively, at the 23/18 degrees C temperature regime. Tetraploid Russian wildrye provides a unique germplasm pool from which additional improvement in seedling vigor can be accomplished beyond the limits that are possible from continued selection in diploid germplasm. The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information. Migrated from OJS platform August 2020