Effect of defoliation management on expression of the 'high sugar' cultivar trait in Tasmania

The proposed benefits of perennial ryegrass (Lolium perenne L.) cultivars with a high concentration of water soluble carbohydrates (WSC) for the dairy industry in Australia include enhanced rumen protein metabolism, and potential improvements in milk components (Stewart et al. 2009). Perennial ryegrass cultivars have been developed to express higher levels of WSC, and extensive trials have shown consistent trait expression in Europe (reviewed by Edwards et al. 2007a). In New Zealand and Australia, there has been less consistent expression of the high sugar trait (Smith et al. 1998; Parsons et al. 2004; Francis et al. 2006), possibly reflecting a genotype by environmental interaction (Parsons et al. 2007). The current study was developed to investigate whether the high sugar trait of cultivars Aber-Magic (developed in Aberystwyth) and SF Joule AR1 (developed in Australia), is consistently expressed in cool temperate Tasmania, Australia, and to quantify the effect of contrasting defoliation management on trait expression. It is also important to confirm that any elevation in WSC concentration does not occur at the expense of dry matter (DM) yield, and to consider the relationship between WSC and crude protein (CP) concentrations - thought to be an important contributor to more efficient nitrogen (N) partitioning (Edwards et al. 2007b).