Seed germination prediction of osmotic-stressed safflower (Carthamus tinctorius L.) at different temperatures using hydrotime analysis

The hydrotime analysis can predict the germination of plants at reduced water potential (ψ). The effects of reduced ψ on seed germination properties in three safflower cultivars including Padideh, Faraman and Isfahan cultivars at 10, 20 and 30 ºC were analyzed using the hydrotime model. Five ψ values (0, -0.3, -0.6, -0.9 and -1.2 MPa) prepared in polyethylene glycol 6000 (PEG) solutions were used in the experiment. The results indicated that all three tested cultivars had the highest germination rate at 30º C and better tolerance to osmotic stress at 20º C. At 20º C, Faraman cultivar had the lowest medium base water potential [ψb(50)]. The standard deviation of ψb (σψb) among cultivars and temperatures could be as high as 0.52 MPa for the Faraman cultivar at 20º. Three tested cultivars had statistically different hydrotime constant (θH) at 10º C. The lowest ψb(50) for achieving 50% germination at 10º C was seen in the Isfahan cultivar, and at either 20º C or 30º C was seen in Faraman and Padideh cultivars. The suppressing effect of drought stress on seed germination was greater in Padideh and Faraman cultivars than that in the Isfahan cultivar. Overall, applying of hydrotime model allowed identifying osmotic stress-tolerant cultivars such as Isfahan during germination; and which might be helpful to seed germination prediction and providing more accurate information for sowing time of safflower.Abbreviations: ψ (water potential); PEG (polyethylene glycol); ψb(50) (medium base water potential); θH (hydrotime constant); σψb (standard deviation of ψb); MGT (mean germination time); FGP (final germination percentage).