High lipid perennial ryegrass growth under variable nitrogen, water and carbon dioxide supply

A novel strategy to increase the metabolisable energy content of pasture species has been the development of a GM technology (‘High metabolisable energy’ or HME), which when expressed in the leaves of perennial ryegrass, increases leaf lipids up to 6-7% of DW (approximately double ‘normal’ levels). Remarkably, increased rates of photosynthesis and growth also occur in these plants. The industry strategy is to perform field trials overseas to establish the value proposition for New Zealand. Here, results are presented from preliminary growth-chamber pot trials which reveal the influence of the HME technology on perennial ryegrass growth under different levels of N, H2O and CO2 supply. HME increased perennial ryegrass growth under high N supply, limiting and non-limiting H2O supply, and with ambient and elevated CO2 supply. Possible HME growth mechanisms and their practical implications are discussed. Progress on the 2017 field trial in the USA using offspring from the HME crossing programme is also discussed.