Differences in tillering of long- and short-leaved perennial ryegrass genetic lines under full light and shade treatments

There is uncertainty among plant breeders as to which characteristics to se lect for to optimize grass growth dynamics. The objective was to study the relationship between leaf length and tillering in perennial ryegrass (Loliu m perenne L.). Two long-leaved and two short-leaved genetic lines were grow n in simulated shade and near-full sunlight (control) environments. The gen etic lines were New Zealand cultivars Ellett (long-leaved) and Grasslands R uanui (short-leaved), both early flowering. The other two were late-floweri ng divergent selections 'LL' (long-leaved) and 'SL' (short-leaved). Differe nces between genetic lines in leaf length were attributable mainly to highe r leaf elongation rate (LER) in the two long-leaved genetic lines, and leaf elongation duration (LED) did not differ significantly between genetic lin es. Grasslands Ruanui bad a higher tiller number per plant than Ellett in b oth light environments, explained by higher site filling but similar leaf a ppearance rate (A(L)). In contrast, LL had a higher tiller number per plant than SL, arising from a higher A(L) in LL. This difference decreased durin g the experiment under the control treatment because SL tended to have a hi gher site filling ratio than LL. However, in the shade treatment, differenc es in tiller number between LL and SL were more mediated by A(L) than site filling. Therefore, selection for high LER and long lamina length, even tho ugh associated with reduced site tilling in all treatments, did not necessa rily result in reduced tiller number per plant.