Cascading functional water balance traits enhance wheat grain yield under terminal drought

Water deficit and high temperatures (i.e. terminal drought) pose a persistent threat to wheat production and sustainability under Mediterranean agroecosystems. We combined open-field, high-throughput gravimetric lysimeters with a field experiment in a rain-out shelter to characterize the physiological response to terminal drought. Two bread wheat genotypes, WM090 (tolerant) and WM036 (susceptible), were selected from a wide diversity panel that was screened over two growing seasons, based on their contrasting yield responses to terminal drought. The superior performance of WM090 was linked to a cascade of water balance-related functional traits. Osmotic adjustment supported greater canopy conductance and sustained transpiration throughout the reproductive phase. The consistent response of canopy temperature and conductance to terminal drought, together with similar yield responses across field and lysimeter platforms, suggests that physiological insights from large-volume lysimeters are transferable to field-grown plants. WM090 also demonstrated higher water use efficiency under terminal drought, throughout multiple years/environments. Transcriptomic profiling revealed 344 differentially expressed genes under terminal drought, among them genes related to osmotic regulation, ion transport, cell wall modification, and light perception. Our findings highlight the potential of integrating spatio-temporal high-throughput phenotyping with molecular tools to promote breeding efforts of wheat adaptability to climate change.