Abstract
Competitive ability can be evaluated in the two distinctive ways : competitive effect, the ability to suppress other individuals and competitive response, the ability to avoid being suppressed. In this study, we examined variation in competitive effect and competitive response among fifteen cultivars of perennial ryegrass (Lolium perenne) and associated traits for a period of two years under sward conditions. A replacement series design with pure swards and equally proportional mixed swards with orchardgrass (Dactylis glomerata) was employed for each cultivar in order to assess competitive ability. Shoot and root morphological traits of each cultivar were also measured under pot conditions. Competitive effect and competitive response were evaluated by relative yield (RY) of D. glomerata and RY of L. perenne, respectively. The results obtained are as follows : (1) There were large differences in competitive effect and competitive response between the cultivars. The differences were more consistent in competitive effect than in competitive response, and in the second year than in the establishment year. (2) The cultivars which suppressed more D. glomerata in the mixture were less suppressed by D. glomerata. Tetraploid cultivars tended to show higher competitive ability than diploid ones. Particularly, the cultivar for turf use was least competitive. (3) The large proportion of variances in relative competitive ability between the cultivars were explained by seed size and morphological traits of shoot and root measured under pot conditions. The cultivars with larger seeds tended to have a higher competitive ability. Competitive ability showed conspicuous correlations with mean tiller weight and number of tillers rather than root and shoot dry matter weight (DM). The cultivars with few but larger tillers tended to have a higher competitive ability than those with more but smaller tillers.
