Competitive Ability in Population of Indian Mustard (Brassica juncea CZERN.et COSS) Bred under High Density Stress

Abstract

In order to study the adaptive strategies of plant population to high density stress, two forms derived from the population of Brassica juncea CZERN. et Coss., one grown for several generations at the high density, about 10, 000 seeds sown per one square meter, (H form) and the other at the low density, 1 plant/m², (L form), were tested in pure- and mixed-culture experiment. The features of two forms show that seed size is larger and flowering time is earlier in the H than in the L form. In dense-sowing (40, 000 seeds/m²) experirnent, both the H and L forms increased the mortality during the juvenile phase (about 30 days after emergence) in both pure- and mixed-stands. But the survival rate of the H form was higher and that of the L form lower in the mixed when compared to the pure-stand. This showed that the H form had the stronger competitive ability at the juvenile phase than the L. In the space plant experiment (20 plants/m2), the H form also could maintain their aggressive growth during both the vegetative and reproductive phases in mixed-stand with the L. These results suggested that under high density stress, survival was correlated with the competitive ability and this character (high competitive ability) was naturally selected. The high competitive ability of the H form (B. juncea) repeatedly reproduced at the high density resulted from its vigorous growth during the juvenile phase.