Using molecular biology techniques to improve our ability to manage pasture

Over the past century, substantial research has been devoted to understanding how different environmental conditions and management practices affect plants. These studies have greatly increased our understanding of factors affecting plant growth and physiology. Modern molecular technologies enable even greater insight into the complex biochemical processes underpinning those responses. In a recent study during winter in Hamilton, New Zealand, gene expression profiling was used to understand the way in which perennial ryegrass (Lolium perenne L.) responded to different defoliation management practices. Plots in perennial ryegrass-dominant pastures were defoliated to 2, 4 or 6 cm residual height and regrown until the 3-leaf stage before determination of pasture yield. Water-soluble carbohydrate (WSC) energy reserves and the expression of photosynthesis genes were monitored throughout the regrowth cycle. Pasture regrowth was reduced by lax defoliation (P <0.001; 2270, 2250 and 1910 kg DM/ha for residual heights of 2, 4 and 6 cm, respectively). Gene expression profiles indicate that plants defoliated to 2 cm increased photosynthesis in stubble tissue at the 1-leaf stage of regrowth, thereby compensating, at least in part, for the reduced leaf area and WSC reserves. This compensatory mechanism is one possible reason why regrowth of pastures defoliated to 2 cm was not compromised. These data confirm the results of previous studies and, for the first time, provide a physiological basis to explain how ryegrass adapts to different grazing management regimes. Use of such confirmatory techniques should give farmers greater confidence in the extended research results and, depending on the technique used, can provide a mechanism for gene discovery.