Rapid and enhanced germination at low temperature of alfalfa and white clover seeds following osmotic priming

Seeds of alfalfa (Medicago sativa) and white clover (Trifolium repens) were primed in 3 priming solutions [2% NaCl, 2% KNO3 and 300 g/L polyethylene glycol (PEG)] for 2 days at 20°C and their subsequent germination compared with that of untreated seed. Four replications of 50 seeds for germination and 25 seeds for emergence were arranged in a 2-factor factorial completely randomised design. All priming treatments significantly (P<0.05) advanced germination rate and percentage of white clover at 15°C, but produced minimal or negative effects on alfalfa. Priming with PEG significantly (P<0.05) reduced time to 50% of final germination percentage (G50 = 4.2 days) of white clover in comparison with control seeds (G50 = 6.5 days). The results indicated that priming seeds in KNO3 for 2 days at 20°C could improve germination rate and germination percentage of white clover at 15oC. Possible reasons for the differing responses in the two species are discussed.