Plant morphology differences in two perennial ryegrass cultivars

'Grasslands Samson' and 'Grasslands Impact' are cultivars of perennial ryegrass (Lolium perenne L.) widely used in New Zealand. This study investigated differences in vegetative morphology of these cultivars. Seeds were germinated, and 50 seedlings per cultivar assessed for 10 different morphological traits in a greenhouse in spring, up to the 10th leaf stage of growth. The cultivars differed most in mean leaf width, leaf-sheath length, leaf appearance interval, and tiller number per plant. 'Grasslands Samson' had broader leaves, shorter leaf-sheaths, a shorter leaf appearance interval, and fewer tillers per plant on average than 'Grasslands Impact', but with overlap between cultivars in all cases. Principal component (PC) analysis of morphological data yielded four PCs judged to contain biological information. PCs 1 and 2 together explained 63% of data variation and identified individual plants of either cultivar with greater leaf length arising from higher leaf elongation rate or leaf elongation duration, respectively. PCs 3 and 4 discriminated between cultivars. Future studies of this type would benefit from the inclusion of a tiller weight measurement not included here. PC analysis of multiple morphological traits appears to provide a useful tool for interpreting alternate forage grass growth strategies.