Effect of drought stress on the germination parameters of Cupressus seeds

To study the effect of drought stress on germination and some physiological characteristics of Cupressus arizonica and C. sempervirens seeds including germination percentage, mean germination time (MGT), germination speed, germination energy, vigor index and recovery percentage, a factorial experiment in completely Randomized Design (CRD) was arranged with five treatments of osmotic potential and 4 replications. The water potential of the germination substrates (0, -2, -4, -6 and -8 bars) was conducted using PEG-6000 solutions. The seeds were kept for 37 days in germinator and 8-16 hours (radiation-darkness) and at 20 ± 0.5°C. The results indicated that drought stress had significant effect on seed physiological characteristics in both species. Decreasing water absorption potential from 0 to -8 bars, significantly reduced germination percentage, speed, energy, and vigor index and increased mean time of germination in both species. The highest recovery percentage was observed in -8 bars. Germination percentage and germination speed, vigor index and recovery percentage of C. sempervirens was better than C. arizonica that probably is more resistant species to drought stress.