Productivity and Morphologic Traits of Thickspike Wheatgrass, Snake River Wheatgrass, and Their Interspecific Hybrids

Abstract

Many rangeland restoration sites in the Intermountain West are environmentally challenging due to low precipitation and invasive species competition; thus, more effective native plant materials are needed. We aim to develop improved Snake River wheatgrass (Elymus wawawaiensis) germplasm through hybridization of this widely used bunchgrass with its nearest relative, the rhizomatous thickspike wheatgrass (E. lanceolatus), followed by backcrossing to Snake River wheatgrass. This approach can potentially introduce desirable adaptive traits from thickspike wheatgrass into Snake River wheatgrass. We measured shoot and root dry matter per plant (DMPP), specific leaf area, C:N ratio, and specific root length (SRL) of nine Elymus populations at two planting densities (25 and 7.8 plants m-2) in two repeated field experiments established from transplants in May 2005 and 2006, both at Millville, Utah. Populations included “Bannock” thickspike wheatgrass; “Secar,” “Discovery,” and three experimental Snake River wheatgrass populations; and three interspecific backcross hybrid populations. Compared with Snake River wheatgrass, the backcross hybrids displayed 10.4 - 33.7% greater shoot DMPP (P < 0.0001) but 12.5 - 16.5% lower root dry matter (DM) density (P < 0.05) across 6 and 2 comparisons, respectively, resulting in reduced root-to-shoot ratio. Compared with Snake River wheatgrass, Bannock displayed 38.6 - 158.2% greater shoot DMPP (P < 0.0001) across six comparisons. In addition, Bannock displayed 22.4% lower SLA (P < 0.01) and 11.1% higher C:N ratio (P < 0.05) than Snake River wheatgrass and the backcross hybrids, traits suggestive of a low-nutrient growth strategy. These data suggest that Bannock achieved its consistently greater shoot DMPP during each growth period despite such a strategy. Hence, its greater productivity likely relates to a superior temporal and/or spatial ability to sequester resources that fuel growth. In this regard, Bannock displayed similar (P > 0.05) or 17% greater (P < 0.05) root DM density and 13.4% greater (P < 0.05) SRL than Snake River wheatgrass, as well as rhizomes.