Abstract Inter-plant competition is a key trait of maize (Zea mays, L.) crops growth and grain yield. Spatial and temporal availability of resources like water, nutrients and radiation have been proved to impact on this trait. It is suspected that light-quality signals operate on plants´ growth variability of irrigated and fertilized maize crops. Since photoreceptors phytochromes B1 and B2 are involved in light-signals-mediated detecting neighbors, it has been speculated that phytochromes B i) affect plants growth variability from early stages of maize cycle, ii) are involved in the increasing inter-plant variability by increasing plant density, and iii) confer a higher competitive capacity of plants within a canopy. It is also unclear if shade avoidance responses are detrimental or beneficial for plants growth and grain yield in maize crops. To test these hypothesis, plants of maize inbred line France 2 wild type (WT) and the isogenic mutants lacking either phyB1 or phyB2 (phyB1 and phyB2), were cultivated in the field during two seasons in monocultures (WT, phyB1, phyB2; hypothesis i and ii) and polycultures (WT/phyB1, WT/phyB2, phyB1/phyB2 and WT/phyB1/phyB2; hypothesis iii) at contrasting plant densities (low and high) irrigated and fertilized. Plant biomass of ten tagged plants per plot were nondestructively estimated from seedling emergence to 15 days after flowering, and from individual samples at physiological maturity and coefficient of variation (CV) of plant biomass was calculated as a proxy of plants growth variability. Plant leaf area, stem length, and plant growth rate of tagged plans were measured around female flowering, i.e. silking (PGRs) and kernel number per plant (KNP) and grain yield were quantified at physiological maturity. At the lower density, no differences in plants growth variability were detected among genotypes. By contrast, at the higher density CV of WT was higher than those of mutant lines only when canopies were fully developed (i.e. after flowering). Taller plants with larger leaf area characterized WT phenotype at all densities and polycultures, which were generally reflected on higher PGRs. These reactions of WT plants allowed them to acquire more competitive ability and to set more KNP and grain yield than phyB1 plants. phyB2 may have offset differences in KNP with WT by greater grain weights. Hence, in maize crops, phytochromes B are key photoreceptors mediating the response of plants growth variability to crowding stress, without any detrimental effect on grain yield because the ability of plants to forage for light, sustains PGRs and kernel setting.

中文翻译：

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光敏色素B对冠层玉米植株生长变异性和竞争能力的影响

摘要 植物间竞争是玉米 (Zea mays, L.) 作物生长和粮食产量的关键性状。水、养分和辐射等资源的时空可用性已被证明会影响这一特性。怀疑光质量信号对灌溉和施肥玉米作物的植物生长变异性起作用。由于光感受器光敏色素 B1 和 B2 参与光信号介导的检测邻居，据推测光敏色素 B i) 从玉米周期的早期阶段影响植物生长变异性，ii) 通过增加植物间变异性参与增加植物间变异性。植物密度，以及 iii) 赋予树冠内植物更高的竞争能力。还不清楚避荫反应是否对玉米作物的植物生长和谷物产量有害或有益。为了验证这些假设，玉米自交系 France 2 野生型 (WT) 和缺乏 phyB1 或 phyB2 的同基因突变体（phyB1 和 phyB2）的植物在田间进行了两个季节的单一栽培（WT、phyB1、phyB2；假设） i 和 ii) 和混养（WT/phyB1、WT/phyB2、phyB1/phyB2 和 WT/phyB1/phyB2；假设 iii）在对比植物密度（低和高）下灌溉和施肥。从幼苗出苗到开花后 15 天无损地估计每块地 10 个标记植物的植物生物量，并从生理成熟时的单个样品和植物生物量的变异系数 (CV) 计算作为植物生长变异性的代表。在雌性开花前后测量标记计划的植物叶面积、茎长和植物生长速率，即 在生理成熟时量化脱丝率 (PGR) 和每株籽粒数 (KNP) 和籽粒产量。在较低的密度下，基因型之间没有检测到植物生长变异性的差异。相比之下，只有在冠层完全发育时（即开花后），WT 的高密度 CV 才高于突变株系。具有较大叶面积的较高植物在所有密度和混养下都具有 WT 表型特征，这通常反映在较高的 PGR 上。WT 植物的这些反应使它们获得了比 phyB1 植物更多的竞争能力并设定了更多的 KNP 和谷物产量。phyB2 可能通过更大的粒重抵消了 KNP 与 WT 的差异。因此，在玉米作物中，光敏色素 B 是调节植物生长变异对拥挤胁迫反应的关键光感受器，