DOI: 10.1007/s11099-016-0193-y PHOTOSYNTHETICA 54 (2): 295-306, 2016 295 Chilling tolerance and early vigour-related characteristics evaluated in two Miscanthus genotypes S. FONTEYNE *,** , P. LOOTENS *,+ , H. MUYLLE * , W. VAN DEN ENDE *** , T. DE SWAEF * , D. REHEUL ** , and I. ROLDAN-RUIZ * Institute for Agricultural and Fisheries Research (ILVO), Plant Sciences Unit, 9090, Melle, Belgium * Ghent University, Department of Plant Production, 9000 Ghent, Belgium ** Katholic University Leuven, Laboratory of Molecular Plant Biology, 3000 Leuven, Belgium *** Abstract A long growing season, mediated by the ability to grow at low temperatures early in the season, can result in higher yields in biomass of crop Miscanthus. In this paper, the chilling tolerance of two highly productive Miscanthus genotypes, the widely planted Miscanthus × giganteus and the Miscanthus sinensis genotype ‘Goliath’, was studied. Measurements in the field as well as under controlled conditions were combined with the main purpose to create basic comparison tools in order to investigate chilling tolerance in Miscanthus in relation to its field performance. Under field conditions, M. × giganteus was higher yielding and had a faster growth rate early in the growing season. Correspondingly, M. × giganteus displayed a less drastic reduction of the leaf elongation rate and of net photosynthesis under continuous chilling stress conditions in the growth chamber. This was accompanied by higher photochemical quenching and lower nonphotochemical quenching in M. × giganteus than that in M. sinensis ‘Goliath’ when exposed to chilling temperatures. No evidence of impaired stomatal conductance or increased use of alternative electron sinks was observed under chilling stress. Soluble sugar content markedly increased in both genotypes when grown at 12°C compared to 20°C. The concentration of raffinose showed the largest relative increase at 12°C, possibly serving as a protection against chilling stress. Overall, both genotypes showed high chilling tolerance for C4 plants, but M. × giganteus performed better than M. sinensis ‘Goliath’. This was not due to its capacity to resume growth earlier in the season but rather due to a higher growth rate and higher photosynthetic efficiency at low temperatures. Additional key words: bioenergy crop; chlorophyll fluorescence; cold tolerance; leaf growth analysis; low temperature stress. Introduction Miscanthus (Miscanthus sp.), a perennial C 4 grass, is in- creasingly used as biomass crop due to its high dry matter yield with limited input of fertilizers, pesticides, and labour (Lewandowski et al. 2000, Anderson et al. 2011). At present, the vast majority of commercial Miscanthus fields are planted with M. × giganteus, a naturally occurring sterile M. sinensis × sacchariflorus hybrid (Greef and Deuter 1993). Dry matter yields of M. × giganteus in temperate and continental regions have been reported as ranging between 10 and 25 t(dry matter, DM) ha –1 (Lewandowski et al. 2003, Zub and Brancourt-Hulmel 2010). Comparisons of M. × giganteus with other species and analysis of the variability present within the genus Miscanthus have highlighted the relevance of a long growing season as a contributor to the observed high yields. For example, Dohleman and Long (2009) concluded that M. × giganteus produces 59% more biomass than maize in the American Midwest because its growing season is ——— Received 23 June 2015, accepted 3 December 2015, published as online-first 28 December 2015. + Corresponding author; e-mail: peter.lootens@ilvo.vlaanderen.be Abbreviations: Chl – chlorophyll; DOY – day of year; Fv/Fm – maximal quantum yield of PSII photochemistry; Fv'/Fm' – quantum yield of open PSII reaction centers; gs – stomatal conductance; LED – leaf elongation duration; LED10–90% – duration of leaf elongation from 10 to 90% of a final length; LER – leaf elongation rate; LERmax – maximum leaf elongation rate; Lm – maximum leaf length; NPQ – nonphotochemical quenching; PN – net photosynthetic rate; qP – photochemical quenching coefficient; Ta – air temperature; WSC – water soluble carbohydrates; ΦCO2 – quantum yield of photosynthesis; ΦPSII – effective quantum yield of PSII photochemistry. Acknowlegdements: The research reported in this article was funded by the European Union's 7 th framework project OPTIMISC (289159). The authors wish to thank Rudy Vergauwen, Robbrecht Cardon, Ellen De Sutter, and Evelien Mortaignie for their help with the measurements and the ILVO technical staff for their help with setting up the experiments.