Abstract
To improve winter hardiness and forage yield in the fall in orchardgrass (Dactylis glomerata L.) for the Hokkaido region, changes in fall dormancy, freezing tolerance and water-soluble carbohydrate (WSC) concentration in crown tissues during cold acclimation in the fall under low temperature and natural short day-length (SDL) and low temperature and 24-hour day-length condition were evaluated using four cultivars of orchardgrass with different levels of winter hardiness. Fall growth was the highest for 'Akimidori' and was lowest for 'Hokkai 28'. 'Hokkai 28' rapidly intensified fall dormancy and freezing tolerance under low temperature and natural SDL condition. Whereas 'Hokkai 28' showed large difference of freezing tolerance between day-length conditions from 7 October to 17 November, that in 'Akimidori' was small. The relationship between WSC concentration and changes of freezing tolerance was not clear in all cultivars. These experiments revealed that 'Hokkai 28' was sensitive to SDL at early stage of cold acclimation whereas 'Akimidori' was not sensitive to it. To develop a superior winter-hardy cultivar of orchardgrass with high fall growth in the Hokkaido region, it is important to increase the growth in late fall and reduce the sensitivity to SDL till early November with maintaining freezing tolerance after middle November.
