Abstract
Occurence of damage in orchardgrass cultivars by continued freezing was investigated. In the first trial, the seedlings of 3 cultivars in pots were hardened at 3℃ for 3 weeks with 8 hours daylength. Thereafter, they were removed from the pots and their crown parts were packed with aluminum foil. The packages were stored in a freezer at -3℃ for 8 weeks. The hardiness of the hardy cultivar increased markedly in an early stage of the storage and was maintained in a high level during 8 weeks, so that no killing was observed. On the contrary, this was not true in the susceptible cultivar and the killing began at 2 weeks after the start of storage. In the second trial, the seedlings of 12 cultivars were treated according to the procedures similar to the first trial and stored at -4℃ for 6 weeks. The tolerance to such a storage condition differed remarkably among the cultivars. Also, a close relationship was found between the percentages of plant survival of the cultivars in the artificial freezing test (-10℃ and -12℃, 16 hours) and those after 2, 4, and 6 weeks of storage. From these results, it was suggested that a prolonged exposure to freezing temperature such as -3℃ or -4℃ was one of the probable reasons why the freezing injury of orchardgrass occured in this area, and that hardier cultivars were more tolerant to such a freezing condition than susceptible ones.
