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 select for to optimize grass growth dynamics. The objective was to study the relationship between leaf length and tillering in perennial ryegrass (Lolium perenne L.). Two long-leaved and two short-leaved genetic lines were grown in simulated shade and near-full sunlight (control) environments. The genetic lines were New Zealand cultivars Ellett (long-leaved) and Grasslands Ruanui (short-leaved), both early flowering. The other two were late-flowering divergent selections 'LL' (long-leaved) and 'SL' (short-leaved). Differences between genetic lines in leaf length were attributable mainly to higher leaf elongation rate (LER) in the two long-leaved genetic lines, and leaf elongation duration (LED) did not differ significantly between genetic lines. Grasslands Ruanui bad a higher tiller number per plant than Ellett in both light environments, explained by higher site filling but similar leaf appearance 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 during the experiment under the control treatment because SL tended to have a higher site filling ratio than LL. However, in the shade treatment, differences 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 though associated with reduced site tilling in all treatments, did not necessarily result in reduced tiller number per plant.