Drought priming improved water status, photosynthesis and water productivity of cowpea during post-anthesis drought stress

Drought occurring at the reproductive stage is the most critical phase affecting cowpea production. It remains unclear whether drought priming at the early growth stage can be employed to alleviate drought stress during the post-anthesis drought period and improve water productivity (WP) in cowpea. Therefore, the physiological responses and WP as affected by drought priming were investigated. Two cowpea varieties (tolerant (V1) and sensitive (V2) to drought stress) were submitted to drought priming followed by water recovery and then subjected to subsequent drought stresses (80%, 60% and 40% of soil water holding capacity (SWHC)). The results showed that cowpea pre-exposed to drought priming acquired a stress imprint that alleviated the subsequent drought stress which occurred during the later growth stage as exemplified by the improvement of water status, photosynthesis, water productivity of biomass (WPb) and yield (WPy) as well as the modulation of plant hormones. Under the drought stress during the post-anthesis period, primed plants maintained lower [ABA]leaf and higher [IAA]leaf than plants without priming due to better plant water status for drought-primed plants. The results revealed that drought priming could modulate against [ABA]leaf increase under drought, as elevated [ABA]leaf was the main reason for stomatal limitation, thereby decreasing photosynthesis and leading to great yield loss. Primed plants consumed 32% and 24% less water for V1 and V2, respectively, which significantly increased WP while decreased intrinsic water use efficiency (WUEi) of drought-primed plants. It is suggested that drought priming during the early growth period can be used as a promising strategy to save water use for irrigation while improving WP of crops in the regions where water is scarce.