Balancing pre- and post-anthesis growth to maximise water-limited yield in cereals

Abstract

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.