1. TIA is a joint venture of the University of Tasmania and the Tasmanian Government Defoliation interval ensures expression of the ‘high sugar’ cultivar trait in Tasmania Lydia R. Turner 1, Daniel J. Donaghy 2, Keith G. Pembleton 1, Richard P. Rawnsley 1 1 Tasmanian Institute of Agriculture, Tasmania, Australia, Private Bag 3523, Burnie, TAS 7320, www.tia.tas.edu.au, Keith.Pembleton@utas.edu.auwww.tia.tas.edu.au 2 Massey University, Palmerston North, New Zealand, www.massey.ac.nzwww.massey.ac.nz Aim To investigate whether the high sugar trait of cultivars AberMagic and SF Joule AR1 is consistently expressed in cool temperate Tasmania, and to quantify the effect of contrasting defoliation management on trait expression. Methods A complete block design experiment was carried out with two treatment factors (cultivar and defoliation interval), and four blocks. Cultivars were AberMagic, SF Joule AR1 and Arrow (control). Defoliation interval treatments were implemented from March 2011 to March 2012, with defoliation management based on the time taken for either 1.5 or 3 leaves per tiller to fully expand (1.5-leaf and 3-leaf stages of regrowth). Herbage dry matter (DM) yield was calculated at each harvest event, and when defoliation intervals coincided leaf samples were collected for analysis of crude protein (CP) and WSC concentrations. Results For all cultivars, higher WSC concentrations were measured at the 3-leaf stage of regrowth than at the 1.5-leaf stage. The mean herbage WSC concentration of AberMagic was consistently higher than that of Arrow throughout the 12-month period. Maintenance of an optimal ratio (> 0.7) of WSC:CP was more strongly influenced by defoliation interval (3-leaf stage > 1.5-leaf stage) than cultivar, although the high WSC cultivars, in particular AberMagic, displayed a higher WSC:CP ratio than Arrow. Under the 3-leaf stage defoliation interval a mean WSC:CP ratio above 0.7 was maintained with greater consistently than under defoliation at the 1.5-leaf stage. The high sugar cultivars yielded as much DM as Arrow over the 12-month measurement period, with all cultivars producing a mean 20% more DM when defoliated at the 3-leaf stage compared with the 1.5-leaf stage (mean 18.0 versus 15.0 t DM/ha). Conclusions The WSC concentration of AberMagic and SF Joule AR1 was consistently higher than that of Arrow, and was not at the expense of DM yield. Expression of the high sugar trait as WSC:CP > 0.7 was maintained through defoliation at the 3-leaf stage of regrowth, suggesting further research should be carried out to quantify the influence of high sugar cultivars on nitrogen (N) partitioning and milk production in Tasmania. Background 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. Perennial ryegrass cultivars have been developed to express higher levels of WSC, and extensive trials have shown consistent trait expression in Europe. In New Zealand and Australia, there has been less consistent expression of the high sugar trait, possibly reflecting a genotype by environmental interaction. Acknowledgements This research was undertaken as part of the Beyond 2012 Project, funded by Dairy Australia Ltd. and delivered by the Tasmanian Institute of Agriculture. Mean water soluble carbohydrate concentration (WSC) and WSC to crude protein ratio (WSC:CP) for each cultivar under 1.5-leaf and 3-leaf stage defoliation intervals. Defoliation interval 1.5-leaf stage3-leaf stage1.5-leaf stage3-leaf stage WSC (%)WSC:CP AberMagic19.4324.720.741.29 Arrow15.3117.770.580.85 SF Joule AR116.9220.530.651.03 P value0.0020.001 LSD0.990.09