Modelling analysis for enhancing seed vigour of switchgrass (Panicum virgatum L.) using an ultrasonic technique

Via modelling analysis, conditions for the ultrasound treatment of switchgrass seeds, including sonication time (factor A), sonication temperature (factor B) and ultrasound output power (factor C), were optimised for stimulating seed vigour of switchgrass seeds using an orthogonal matrix design [L16 (45)]. Germination percentage (GP) and the seed vigour index (Iv) were used as indicators of seed vigour. The results demonstrate that factor B has the largest effect on seed vigour, followed by factor A and then factor C. Combined with the range analysis, variance and models, the final optimal ultrasonic treatment conditions were found to be a sonication time of 25 min, sonication temperature of 38 °C and output power of 300 W. Additionally, water uptake tests with three treatments (control, soaking in water only and then redried and ultrasound treatment and then redried) were performed to investigate further details of the mechanisms for stimulating germination using ultrasound. The mean seed moisture of the seeds only soaked in water and treated by ultrasound was, respectively, 47.70% and 91.88% higher than that of control seeds. The results of the imbibition tests show that both water and ultrasound per se play important roles in increasing water uptake at the early stage of soaking. The results above provide a basic demonstration for applying ultrasound to pretreat switchgrass seeds.