[Objective] To alleviate the summer-overing problem and screen out good heat-resistant varieties of perennial ryegrass. [Method]Three species of perennial ryegrass Nui,Mathilde and Yatsyn were used as research objects to make high temperature stress. The effects of high temperature stress on the seedling characteristics of perennial ryegrass were studied by determining the germination and seedlings' characteristics. [Result] Under high temperature stress,the relative germination rate,relative germination in...