Bromegrass species are important forage crops in temperate regions of world. This study compared responses of three bromegrass species to defoliation in the greenhouse and field to determine if the former could predict responses in the latter. Experiments were conducted in 2006 and 2007 in Saskatoon ( N, W), Canada on meadow bromegrass (Bromus riparius Rehm.), smooth bromegrass (Bromus inermis Leyss.), and hybrid bromegrass (B. riparius X B. inermis) following defoliation to 5 cm stubble height. When defoliated at the vegetative stage, above-ground biomass was similar among the three species in the field, but meadow bromegrass produced greater above-ground biomass than smooth bromegrass in the greenhouse. When defoliated at the stem elongation stage, meadow bromegrass produced greater above-ground biomass than smooth bromegrass in both environments. In the field, for all defoliation treatments, tiller number was greatest in meadow bromegrass, intermediate in hybrid bromegrass, and least in smooth bromegrass. In the greenhouse, however, the three species did not differ in tiller number. Similar results were found for below-ground biomass. Thus, testing the effect of defoliation in the greenhouse environment did not accurately predict the effect in the field environment. 1. Introduction Smooth bromegrass and meadow bromegrass are perennial, cool-season grasses widely cultivated for pasture and hay in temperate regions of world. Meadow bromegrass is well adapted to grazing due to its rapid regrowth after defoliation [1], while smooth bromegrass is intolerant to frequent defoliation and generally used for hay [2]. The hybrid bromegrass cultivar “Knowles” was recently developed by hybridizing smooth and meadow bromegrass and has potential for both hay and pasture use [3]. A number of studies have been conducted in the field to understand morphological and physiological characteristics of the three bromegrass species in response to defoliation [1, 4–7]; however, little information is available on how these three species respond to defoliation under different growth environments. In cool-season grasses, the optimum temperature for growth varies among species [8]. Leaf appearance and elongation rate are often reduced by low temperature and moisture level [9, 10]. High temperature inhibits tillering because of high respiration rates and lower soluble carbohydrate concentrations in the plant [8]. The ability of grasses to produce tillers is sensitive to changes in light intensity and quality. Tiller density increases with increasing light intensity [11] and high
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