An Experimental Study of Competitive Performance in Brassica rapa (Cruciferae)

Growth chamber experiments with rapid-cycling Brassica rapa were designed to estimate the signsand magnitudes ofthe genetic correlationsfor plant performance in each ofthree conditions: no-competition (isolated plants), intraspecific competition, and interspecific competition with Raphanus sativa. Biomass and flower number were highest in the no-competition treatment, intermediate under intraspecific competition, and lowest under interspecific competition. Significant among-family variation in biomass and flower number was found under each regime. The mean family performance (biomass or flower number) in the no-competition treatment was significantly positively correlated with the performance in only one of the competitive treatments (for biomass in the intraspecific treatment). For both biomass and flower number there was a significant positive correlation between family means in the intraand interspecific regimes. These correlations were greater in magnitude than those for the comparison between no-competition and competition (intraor interspecific) treatments. Our results suggest that the importance of traits affecting plant performance is environment-dependent; the performance of a family grown without competition was a poor predictor of performance with competition, while the performance offamilies grown under intraand interspecific competition was positively