Effect of gibberellin soaking on seed germination of perennial ryegrass under polyethylene glycol simulated drought conditions

To study the effects of gibberellin soaking on the germination of perennial ryegrass (Lolium perenne) seeds, germination indices were investigated under simulated drought conditions. The perennial ryegrass ‘Mathilde’ was soaked with four concentrations of gibberellin: 0, 100, 200, and 300 mg·L^–1. After 24 h of seed soaking, the germination test was performed under Polyethylene glycol (PEG) stress at different concentrations (0, 5%, 10%, and 15%). The germination potential was measured on the fifth day, and the germination rate, bud length, root length, bud inhibition rate, root inhibition rate, and root-shoot ratio were measured on the fourteenth day. The results showed that with the increase in drought stress, the germination potential, germination rate, and bud length of perennial ryegrass showed a decreasing trend, and the root length first increased and then decreased. Gibberellin treatment had no significant effect on seed germination rate under 0, 5%, and 10% PEG stress; however, soaking in 200 mg·L^–1 and 300 mg·L^–1 gibberellin could significantly alleviate the inhibitory effect of drought on the seed germination rate of perennial ryegrass under 15% PEG stress. The seed soaking treatment (200 mg·L^–1 and 300 mg·L^–1) could reduce the rate of bud inhibition and increase the root-shoot ratio of perennial ryegrass under various drought stresses. In conclusion, the optimum concentration of gibberellin for inducing seed germination, enhancing seedling growth, and alleviating drought stress of perennial ryegrass was 200～300 mg·L^–1.