Effects of seed priming with gibberellic acid on cardinal temperatures of Borage (Borage officinalis L.) seed germination

This experiment was conducted at seed technology laboratory of Agricultural Sciences and Natural Resources University of Khuzestan, in 2018 with the to evaluate the effects of seed priming on cardinal temperatures and thermal time requirements of borage seed germination. The factorial experiment was arranged based on the randomized complete block design with three replications. Treatments were gibberellic acid (0 (distilled water as control), 100, 200, 400 mg/L-1), priming durations (6 and 12 hour) and seven levels of germination temperatures (5, 10, 15, 20, 25, 30 and 35 oC). Beta model, beta modified, dent-like and segmented were used to determine cardinal temperatures. Results showed that seed germination significantly increased at both priming durations of 6 and 12 hours with increasing of temperature and gibberellic acid concentrations. The highest seed germination was observed at 200 mg/L-1gibberellic acid and 15 oC. Increase of gibberellic acid concentrations resulted higher thermal time requirements to complete 50% of germination in seed population. From the results, the beta model provided the best fit to evaluate cardinal temperatures of borage seeds. It is therefore, suggested that the base, optimum and celling temperatures of borage seeds are 0.51, 21.5 and 35.1 oC and influenced by application 200 mg/L-1GA to 0.33, 23.5 and 35.8 oC.