Cytogenetics of Eurasian Bluebunch Wheatgrass and Their Relationship to North American Bluebunch and Thickspike Wheatgrasses

Bluebunch wheatgrass, Pseudoroegneria spicata (Pursh.) A. Love, is one of the most important native dryland forage bunchgrasses of the intermountain West, which often produces depleted stands under moderate to heavy grazing pressure. In recent plant collecting trips to the Altai and Tien Shan Mountains of China and Russia, a grazing tolerant bluebunch wheatgrass complex was obtained. This study was conducted to describe the cytogenetic characteristics and potential for genetic exchange between the Eurasian bluebunch wheatgrass complex [P. strigosa (M. Bieb.) A. Love, P. geniculata (Trin.) A. Love, Roegneria elytrigioides Yen and Yang, and R. glaberrima Keng et S.L. Chen] and those bluebunch thickspike wheatgrasses found in North America. Meiotic behavior of the triploid hybrids between diploid and tetraploid R. glaberrima indicated that both ploidy levels share the same genome. Almost complete pairing in hybrids P. strigosa ssp. aegilopoides (Drob.) A. Love × P. spicata, and R. glaberrima × P. spicata, demonstrated that P. strigosa ssp. aegilopoides and R. glaberrima are comprised of the basic S genome. Triploid hybrids between P. geniculata, and R. elytrigioides with either P. spicata, P. stipifolia (Czern. ex Nevski) A. Love, or P. strigosa ssp. aegilopoides exhibited trivalent frequencies consistent with the hypothesis that tetraploid R. elytrigioides is an autotetraploid (SSSS) and that P. geniculata is either a segmental autotetraploid (S1S1S2S2) or an allotetraploid (SS??). Based on the high level of chromosome pairing in the interspecific hybrids between the Eurasian and North American bluebunch wbeatgrass complex, genetic exchange is possible. Due to the close genetic and morphological similarity among individuals of P. spicata, P. strigosa, P. geniculata, R. elytrigioides, and R. glaberrima we are likely dealing with a single, polymorphic, Eurasian‐North American species complex.