The physiology of shade avoidance

作物和杂草之间的竞争传统上被认为是对光、水和养分等资源的争夺。杂草造成作物减产的生理机制尚不清楚。通过红远红比（R:FR）早期发现邻近植物可能是影响植物间竞争的重要机制。作物植物可以检测到由于邻近杂草的存在而引起的R:FR比的变化，因此最初会长得更高，分枝更少，根系发育更少。这种避荫反应可能会延迟物候发育，并以生殖健康为代价。以前没有研究将R:FR比值的早期检测作为解释作物和杂草竞争结果的机制。在本研究中，笔者拟探讨杂草引起玉米和大豆避荫反应的生理和分子机制。初步研究发现，玉米和大豆种质资源对杂草叶片表面反映的R:FR有广泛的表型响应。我计划在作物变异中使用这一方法来探索以下假设：目标1：确定对R:FR响应不同的玉米杂交品种和大豆品种在其发育过程中是否受到表型限制，在生物量积累方面是否表现不佳。目的2：确定对R:FR反应不同的玉米杂交种和大豆品种是否经历了相似的避荫成本，通过对随后的非生物胁迫的表型可塑性丧失或以产量损失表示。目的3：发现玉米杂交种和大豆品种对R:FR比的不同反应是否存在与杂草诱导避光相关的关键代谢和信号通路的改变。从这项研究中获得的新知识将被植物育种者用于开发更具抗逆性的玉米杂交品种和大豆品种。

Competition between crop and weed has been regarded traditionally as a struggle for resources such as light, water and nutrients. The physiological mechanism by which weeds cause yield losses in crops is understood poorly. Early detection of neighbouring plants through the red-to-far red (R:FR ) ratio may be an important mechanism affecting plant to plant competition. Crop plants can detect changes in the R:FR ratio caused by the presence of neighbouring weeds and as a result will grow initially taller, with less branching and less root development. This shade avoidance response may delay phenological development and come at a cost to reproductive fitness. No study has been conducted previously to associate the early detection of the R:FR ratio as a mechanism to explain the outcome of crop and weed competition. In this study, I propose to explore the physiological and molecular mechanisms involved in the shade avoidance response of corn and soybean caused by the presence of weeds. Preliminary research has identified a wide range in corn and soybean germplasm phenotypic response to R:FR ratio reflected from the leaf surface of weeds. I plan to use this within crop variation to explore the following hypotheses: Objective 1: to determine if corn hybrids and soybean cultivars differing in response to R:FR are constrained phenotypically during their development and perform suboptimally in terms of biomass accumulation. Objective 2: to determine if corn hybrids and soybean cultivars differing in response to R:FR experience a similar cost of shade avoidance, as measured by a loss of phenotypic plasticity to subsequent abiotic stresses or expressed as yield loss. Objective 3: to discover if alterations exist in key metabolic and signalling pathways associated with weed-induced shade avoidance in corn hybrids and soybean cultivars that differ in their response to R:FR ratio. New knowledge generated from this study will be used by plant breeders to develop more stress tolerant corn hybrids and soybean cultivars.