404 G. CHEN, Q.Z. WANG, Y. LIU, Y.B. LI, J. CUI, Y.Y. LIU, J.M. CHENG AND Ð. KARAGIC ´ * Author for correspondence Chen, G., Wang, Q.Z., Liu, Y., Li, Y.B., Cui, J., Liu, Y.Y., Cheng, J.M. and Karagic´, Ð. (2012), Seed Sci. & Technol., 40, 404-412 Optimisation of sonication conditions to enhance seed vigour in switchgrass (Panicum virgatum) G. CHEN 1 , Q.Z. WANG 1 *, Y. LIU 1 , Y.B. LI 1 , J. CUI 2 , Y.Y. LIU 1 , J.M. CHENG 3 AND Ð. KARAGIC ´ 4 1 Department of Grassland Science, College of Animal Sci. and Techn., Northwest A&F University, Yangling 712100, Shaanxi Province, P.R. China (E-mail: wangquanzhen191@163.com) 2 Department of Plant Science, College of Life Science, Northwest A&F University, Yangling 712100, Shaanxi Province, P.R. China 3 State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation of CAS & MWR 4 Institute of Field and Vegetable Crops, Forage Crops Department, Maksima Gorkog 30, 21000 Novi Sad, Serbia (Accepted July 2012) Summary Switchgrass (Panicum virgatum) is a valuable forage grass and shows great potential as a renewable biofuel crop. In establishment from seed, the failure of the seeds to germinate can lead to reductions in plant growth and final crop yield. Using an orthogonal matrix design, sonication treatment conditions were optimised to enhance switchgrass seed vigour. Three factors, sonication time (A), temperature (B) and ultrasound output power (C), were considered. Seed germination potential, mean germination time and germination rate index were used as parameters of seed vigour. Sonication temperature was identified as the factor with the largest effect on switchgrass seed vigour, followed by sonication time and ultrasound output power. Maximal seed vigour was obtained by sonication for 25 minutes at 35°C with an output power of 200W. These results provide the basis for using ultrasound to enhance switchgrass seed vigour. Introduction Switchgrass (Panicum virgatum L.) is a perennial warm-season grass, that is a valuable forage in many countries because of its fast growth and high yield (Mitchell et al., 2001; Sanderson, 2008). Furthermore, because of its abundant biomass, strong resistance, broad adaptability and ease of management, switchgrass can produce stable yield on marginal land, thus showing great potential as a renewable biofuel crop (Das and Taliaferro, 2009; Grassini et al., 2009; Gunter et al., 2003). Increasing worldwide demand for energy, instability in oil-producing countries and growing concerns about global warming and atmospheric pollution have led to a surge in switchgrass research. The organic compounds obtained from switchgrass (cellulose,