ABR: Response to Crowding and Vegetation Shade in Impatiens capensis: Genetic Basis and Fitness Consequences

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Many plant species exhibit characteristic morphological and physiological responses to crowding and vegetation shade. This "shade avoidance" response is cued by a reduction in the ratio of red to far-red wavelengths (R:FR) in light transmitted through or reflected from green vegetation. This R:FR signal is perceived by light-sensing molecules known as phytochromes. Prior research from this project has demonstrated that phytochrome-mediated stem elongation increases lifetime reproduction of the native annual Impatiens capensis (jewelweed or touch-me-not) in dense stands, but plants induced to display the shade avoidance response at low density suffer reduced fitness relative to non-elongated plants. The present study will examine genetic variation among inbred lines in expression of shade avoidance traits across a range of densities, and assess the contribution of phytochrome-mediated developmental pathways to this variation. In addition, natural selection on shade avoidance traits will be measured in the field across a range of densities, in order to predict how shade avoidance responses will evolve in variable density environments. The results of this project will provide important information about the genetics and evolution of phytochrome-mediated shade avoidance responses in natural plant populations, and will provide an ecological and evolutionary context for current research on the molecular, genetic, developmental, and physiological mechanisms underlying plant responses to light. It will also help to inform selection strategies for crop improvement and provide an ecological context for recent proposals to increase yield by genetically engineering crops in which shade avoidance responses are blocked.