Assessing Genotypic Variability of Switchgrass Seed Germination in Response to Temperature.

Temperature plays a major role in seed germination and early seedling establishment of switchgrass (Pancium virgatum L.), an important native warm-season species with feedstock potential for the cellulosic biofuel industry.  Developing growth models for switchgrass require cultivar-specific temperature response functions for seed germination. An experiment was conducted to determine the effects of temperature on seed germination of 14 switchgrass genotypes.  Stratified seed of each genotype were germinated on moistened filter paper in Petri dishes at eight constant temperatures from 12.5 to 42.5 degree centigrade and under a constant light intensity of 35 µmol per meter square per second for 12 h a day.  The number of seed germinated was recorded at six hour interval at each temperature for all genotypes.  The germination response to temperature was modeled using a three-parameter logistic function which defined the maximum cumulative germination percentage (germination capacity), the shape and steepness (rate) of germination, and the speed (time to 50% of maximum) of germination.  Cardinal temperatures (Tbase, Topt and Tmax) and temperature adaptability range (TAR, Tmax – Tbase) for each genotype were determined from these parameters.  Cardinal temperatures, maximum germination percentage, and TAR were varied among switchgrass cultivars and these parameters were used to classify the genotypes for their tolerance to low and high temperatures.