Comparison of germination criteria in red fescue (Festuca rubra ssp litoralis), perennial ryegrass (Lolium perenne) and Kentucky bluegrass (Poa pratensis)

Several different germination criteria are used in germination studies. The aim of this study was to evaluate three different germination criteria in three grass species by comparing each criterion with the normal seedling criterion and by comparing mean germination time (MGT). The three species were slender creeping red fescue (Festuca rubra ssp. litoralis), perennial ryegrass (Lolium perenne) and Kentucky bluegrass (Poa pratensis). The three criteria were based on the emergence of a radicle (greater than or equal to2 mm), a coleoptile (greater than or equal to2 mm), or a cotyledon from the coleoptile (greater than or equal to1 mm). All three criteria provided results that had strong linear relationships with percentage normal seedlings with overall standard error not exceeding 1.52% (R-2 = 0.95 to 0.97). For all criteria, the relationship had slopes significantly different from one and intercepts significantly different from zero. Thus, all three criteria tended to overestimate the number of normal seedlings slightly, particularly at lower germination percentages. The variation in percentage of normal seedlings was best described by the radicle criterion and poorest by the coleoptile criterion, but the differences were very small. We suggest that choice of criteria should be determined by the convenience of assessing the different seedling structures.