To maximize cereal yield in water-limited environments where crops rely on stored soil moisture, pre-anthesis growth and water-use must be balanced to create a sink demand at anthesis that can be filled by the remaining water after anthesis. We hypothesize that canopy development in cereals is a key regulator of biomass and water allocation before and after anthesis, affecting stem reserve mobilization, nitrogen dynamics and grain yield in water-limited environments. In drought-prone regions where crops heavily depend on stored soil moisture, crops facing end-of-season drought must conserve water during early growth to ensure that sufficient water is available for grain filling. To better understand this balance, we expressed the ratio between post- and pre-anthesis biomass as an index, designated as the ‘biomass rationing index’ (BRI). This index was evaluated in three cereal species (sorghum, wheat and barley) in multiple seasons and environments to examine the extent to which it could be manipulated by genetics and management. BRI was negatively correlated with canopy size at anthesis and was positively correlated with stay-green, change in post-anthesis stem biomass, nitrogen content at maturity, and ultimately grain yield. Results suggest that post-anthesis water availability was closely linked to pre-anthesis green leaf area and biomass, and that at least in environments where crops relied on stored soil moisture, limiting canopy size was an effective strategy to ensure adequate water availability for grain filling in the face of end-of-season drought. A range of genetic strategies (genes regulating tillering, leaf size, stomatal conductance, transpiration per leaf area, hydraulic resistance, root architecture) and management strategies (pre-crop factors, plant density, nitrogen fertilization, weed control, crop rotations, weed control, soil type) could be used to manipulate BRI.We propose BRI as a simple indicator to provide new insights on how water-limited yield in cereals can be maximized by better balancing pre- and post-anthesis growth.

为了在作物依赖储存的土壤水分的缺水环境中最大限度地提高谷物产量，必须平衡开花前的生长和用水，以在开花期产生库需求，而开花期后剩余的水可以补充该库。我们假设谷物的冠层发育是开花前后生物量和水分分配的关键调节因子，影响水分有限环境中的茎储备动员、氮动态和谷物产量。在作物严重依赖储存的土壤水分的干旱易发地区，面临季末干旱的作物必须在早期生长期间保存水分，以确保有足够的水用于灌浆。为了更好地理解这种平衡，我们将开花后和开花前生物量的比率表示为一个指标，指定为“生物量配给指数”(BRI)。该指数在多个季节和环境中对三个谷物品种（高粱、小麦和大麦）进行了评估，以检查它可以在多大程度上被遗传学和管理所操纵。BRI 与开花时的冠层大小呈负相关，与保持绿色、开花后茎生物量的变化、成熟时的氮含量以及最终的谷物产量呈正相关。结果表明，开花后的水分供应与开花前的绿叶面积和生物量密切相关，至少在作物依赖储存的土壤水分的环境中，限制冠层大小是确保灌浆充足水分的有效策略面对季末干旱。一系列遗传策略（调节分蘖、叶片大小、小麦和大麦）在多个季节和环境中进行研究，以检查遗传学和管理对其进行操纵的程度。BRI 与开花时的冠层大小呈负相关，与保持绿色、开花后茎生物量的变化、成熟时的氮含量以及最终的谷物产量呈正相关。结果表明，开花后的水分供应与开花前的绿叶面积和生物量密切相关，至少在作物依赖储存的土壤水分的环境中，限制冠层大小是确保灌浆充足水分的有效策略面对季末干旱。一系列遗传策略（调节分蘖、叶片大小、小麦和大麦）在多个季节和环境中进行研究，以检查遗传学和管理对其进行操纵的程度。BRI 与开花时的冠层大小呈负相关，与保持绿色、开花后茎生物量的变化、成熟时的氮含量以及最终的谷物产量呈正相关。结果表明，开花后的水分供应与开花前的绿叶面积和生物量密切相关，至少在作物依赖储存的土壤水分的环境中，限制冠层大小是确保灌浆充足水分的有效策略面对季末干旱。一系列遗传策略（调节分蘖、叶片大小、BRI 与开花时的冠层大小呈负相关，与保持绿色、开花后茎生物量的变化、成熟时的氮含量以及最终的谷物产量呈正相关。结果表明，开花后的水分供应与开花前的绿叶面积和生物量密切相关，至少在作物依赖储存的土壤水分的环境中，限制冠层大小是确保灌浆充足水分的有效策略面对季末干旱。一系列遗传策略（调节分蘖、叶片大小、BRI 与开花时的冠层大小呈负相关，与保持绿色、开花后茎生物量的变化、成熟时的氮含量以及最终的谷物产量呈正相关。结果表明，开花后的水分供应与开花前的绿叶面积和生物量密切相关，至少在作物依赖储存的土壤水分的环境中，限制冠层大小是确保灌浆充足水分的有效策略面对季末干旱。一系列遗传策略（调节分蘖、叶片大小、至少在作物依赖储存的土壤水分的环境中，限制冠层大小是一种有效的策略，可确保在面临季末干旱时谷物灌浆有足够的水供应。一系列遗传策略（调节分蘖、叶片大小、至少在作物依赖储存的土壤水分的环境中，限制冠层大小是一种有效的策略，可确保在面临季末干旱时谷物灌浆有足够的水供应。一系列遗传策略（调节分蘖、叶片大小、气孔导度、每叶面积蒸腾、水力阻力、根系结构）和管理策略（作物前因素、植物密度、施氮肥、杂草控制、作物轮作、杂草控制、土壤类型）可用于操纵 BRI。我们建议BRI 作为一个简单的指标，可以提供关于如何通过更好地平衡开花前和开花后生长来最大化谷物水分限制产量的新见解。