Abstract
Drought limits crop productivity and threatens global food security, with moderate drought stress — when crops grow at a reduced rate — commonly experienced. Increasing plant tolerance to moderate drought is a key target for adaptation and management, but efforts to understand and increase drought tolerance often focus on more extreme drought that causes complete crop failure and only consider crop genetics. In this Review, we discuss the influence of moderate drought on crop productivity and the role of physiological traits in drought tolerance and adaptation. Traits related to crop water use, water capture, water availability, transpiration efficiency and phenology impact drought adaptation, but their overall effect varies situationally. For example, early restrictions in transpiration, higher transpiration efficiency or altered tillering increase water availability during grain filling and can double yield in some drought scenarios. However, these same traits under less severe drought scenarios can also lead to yield penalties. To assess when and under what conditions traits will be beneficial, crop models are used to integrate the effects of genetics, the environment and management, estimating the expected yield responses under these combinations of scenarios and traits. More robust characterization of moderate drought tolerance and better integration between plant genetic information and modelling will enable the local selection of crop varieties suited to the expected drought scenarios.