The physiology of shade avoidance

作物和杂草之间的竞争传统上被视为对光、水和养分等资源的争夺。杂草导致农作物减产的生理机制知之甚少。通过红远红光比(R：FR)及早发现邻近植物可能是影响植物间竞争的重要机制。农作物可以检测到相邻杂草引起的R/FR比率的变化，结果是最初会长得更高，分枝更少，根的发育也更少。这种遮荫回避反应可能会延迟物候发育，并以生殖适合性为代价。以前还没有研究将R：FR比的早期检测作为解释作物和杂草竞争结果的机制。在这项研究中，我打算探索玉米和大豆在杂草存在下的避荫反应的生理和分子机制。初步研究已经确定玉米和大豆种质对杂草叶表面反映的R：FR比率的表型反应范围很广。我计划在作物变异中利用这一点来探索以下假设：目标1：确定对R：FR反应不同的玉米杂交种和大豆品种在其发育过程中是否受到表型限制，并在生物量积累方面表现为次优表现。目的：确定对R：FR反应不同的玉米杂交种和大豆品种是否经历相似的避荫成本，通过对后续非生物胁迫的表型可塑性丧失或表现为产量损失来衡量。目的3：研究玉米杂交种和大豆杂交种是否存在与杂草诱导遮荫相关的关键代谢和信号通路的改变，这些杂交种和大豆品种对R/FR比值的反应不同。这项研究产生的新知识将被植物育种者用来培育更耐逆境的玉米杂交种和大豆品种。

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.