Plasticity of Yield Components in Response to Stress in Sesbania macrocarpa and Sesbania vesicaria (Leguminosae)

Abstract

The effects of limited moisture, limited nutrients, the defoliation on the subsequent allocation to yield components were measured in Sesbania macrocarpa and S. vesicaria in order to test the hypotheses that all yield components might be involved in the regulation of reproduction and that patterns of plasticity in reproduction may be species-specific. In S. vesicaria, the number of fruits per flower was the only yield component consistently reduced below the control. In S. macrocarpa, the responses to mild stress were reductions in the number of seeds per ovule and in seed weight, components of yield probably determined later than the number of fruits per flower. Severe stresses resulted in a change in flower number. Both the pattern and the amount of plasticity in yield components differed significantly between the species. Differences in responses to the same stresses may represent different adaptations resulting from variation in the importance of each component of yield for the successful reproduction of the two species in slightly different habitats. Within species, half-sib families differed in the amount, but not in the kind, of plastic response. Each species appears to be genetically invariant for plastic response differed between the species. Perhaps developmentally early yield components are genetically fixed to be either variable or stable, and responses in developmentally later yield components are determined by the levels of change in the earlier yield components.