Abstract
Ten cultivars of red clover (Trifolium pratense L.), including one foreign cultivar and nine Japanese cultivars or breeding lines, were tested for local adaptability at five different locations in Hokkaido from 1986 to 1989. Principal component analysis was applied to data on annual dry matter yields of the ten cultivars at the five locations during a period of four years. The locations were divided into two groups : one group of three locations in the northern or western part of Hokkaido and one group of two other locations in the eastern part of Hokkaido. The former group is in a snowy area, and the latter group is in a less-snowy, soil-freezing area. The ten cultivars were divided into two groups : one group consisting of six cultivars that showed good yield in the snowy area and one group consisting of four cultivars that showed good yield in the less-snowy soil-freezing area. The former group of cultivars showed relatively weak vigor at aftermath growing, while the latter group showed strong vigor. Red clover plants often suffer from clover rot in a snowy area but rarely suffer from clover rot in a soil-freezingarea. It could be concluded that the difference between the two groups of cultivars with respect to local adapatbility was due to the difference in their ability to resist clover rot caused by Sclerotinia trfoliorum.
