Effect of a stay-green locus on the dry-matter yield, nitrogen yield and shoot density of perennial ryegrass

A rare stay-green allele transferred from meadow fescue (Festuca pratensis L.) to perennial ryegrass (Lolium perenne L.) has improved both the colour of turf and the nutritive value of herbage. In this study its effect on shoot density and forage yield was assessed. Equivalent populations of perennial ryegrass were constructed with and without the stay-green allele, following eight generations of backcrossing to perennial ryegrass. The stay-green population, the normal population and the cv. AberStar were compared over two harvest years (2005 and 2006) in a field experiment with six application rates of N fertilizer (100, 200, 300, 400, 500 and 600 kg ha−1 annually). There were no significant interactions between level of N fertilizer and population in any of the traits measured. The mean annual dry-matter (DM) yield over all populations and fertilizer levels was 6·45 t ha−1 lower in the second harvest year. Mean annual DM yields over all fertilizer levels of the normal population were higher than, or equal to, AberStar while those of the stay-green population were significantly (proportionately 0·10–0·13) lower than the normal population. In 2005, the mean total yield of N in the herbage of the stay-green population was 0·09 lower than that of the normal population and the mean concentration of N over all harvests was 1·5 g kg−1 DM higher. The shoot density of the stay-green population after the last harvest in November 2006 was 0·18 lower than that of the normal population (3689 and 4478 shoots m−2 respectively).