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. WM090's superior performance 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.