Ashraf and Abu-Shakra, 1978; Hao and de Jong, 1988). Several studies have indicated that germination is de-Oat (Avena sativa L.) yield and quality on the northern Great layed and reduced by low water potential (Rao and Plains are consistently reduced by frequent drought and wild oat Dao, 1987; Hao and de Jong, 1988), low temperature (Avena fatua L.) competition. Wild oat cannot be selectively removed (Livingston and de Jong, 1990; Willenborg et al., 2004), from oat with herbicides. Identifying genotypes or seed size(s) with high germination potential under moisture stress may facilitate im-high salinity (Romo and Haferkamp, 1987), and combiproved seedling vigor, stand establishment, and crop competitiveness.nations of these factors (Willenborg et al., 2004; Living-Therefore, a germination study was conducted to determine the effects ston and de Jong, 1990; Hao and de Jong, 1988). The of genotype and seed size on the germination of oat seed subjected resulting late and inadequate germination and subseto moisture stress. Large, medium, and small seeds of six common quent seedling establishment critically affect crop prowestern Canadian oat genotypes were germinated in polyethylene duction this region (Livingston and de Jong, 1990). glycol (PEG 8000) solutions with initial osmotic potentials rangingOat is one of the major economic grain crops grown from 0 to Ϫ0.4 MPa at 5؇C. Generalized linear mixed models fit to in the northern Great Plains region, planted annually the data provided a statistically valid, appropriate, and convenient on 1.7 million hectares of land in western Canada alone method to analyze germination data. In all genotypes examined, de-(Statistics Canada, 2004). Oat is a crop that normally creasing seed size and osmotic potential increased median germination time (MGT) and lowered final germination percentage (FGP). Among produces seed of varying size as a result of the multigenotypes, CDC Bell had the fastest MGT while AC Mustang had floret habit of the oat spikelet (Doehlert et al., 2002, the highest FGP. Delays in MGT and reductions in FGP resulting 2004). Oat seed size is inherently nonuniform because oat from increased moisture stress were similar to those observed in other may produce one, two, or three seeds per spikelet. The cereals, suggesting that oat may be as capable of germinating under innermost seed, called the primary seed, is the largest low spring soil moisture conditions as wheat and barley. The results and seed size and mass decrease with increasing seed of this study also indicate that large seed of genotypes such as AC order (Doehlert et al., 2002). This relationship results Mustang and CDC Bell appear better suited to germinate under the from reduced sink strength and photoassimilate acquirange of osmotic potentials in this study. Although differences in sition of higher order seeds (Palagyi, 1983; Doehlert et MGT and FGP between seed sizes in this study were statistically al., 2002).significant, they were generally small and thus, oat germination characteristics may not be...