Waterlogging stress reduces cowpea (Vigna unguiculata L.) genotypes growth, seed yield, and quality at different growth stages: Implications for developing tolerant cultivars under field conditions

Waterlogging is a significant abiotic stress that reduces the oxygen supply to roots in the rhizosphere, impairing plant growth and development. Cowpea is highly sensitive to waterlogging, and their grain yield is affected by genotype and growth stage. Understanding the growth and physiological responses of cowpea to waterlogging stress is crucial for developing strategies to improve crop yield in waterlogged environments. In this two-year field trial, we quantified the impact of ten days of waterlogging on morpho-physiological attributes, seed yield components, and seed quality of two cowpea genotypes (UCR 369 and EpicSelect.4) at different growth stages. Waterlogging during the reproductive (R2) growth stage had the most substantial impact on cowpea, with an average reduction of leaf area by 65%, chlorophyll content by 39%, stomatal conductance (gs) by 93%, and photochemical efficiency by 32% compared to non-waterlogged plants. These effects were less pronounced during the vegetative (V4) and physiological maturity (R7) growth stages. Lower photosynthetic capacity resulted in reduction of biomass accumulation, pod dry weight, number of pods per plant, and seed weight under waterlogging. EpicSelect.4 was more sensitive to waterlogging at the R2 stage, showing a greater reduction in seed yield (58%) compared to UCR 369 (46%). Additionally, UCR 369 maintained seed protein content under waterlogging conditions, while it decreased by 8% in EpicSelect.4 seeds. Overall, UCR 369 was more tolerant to waterlogging stress than EpicSelect.4, with the most apparent effect of waterlogging on yields occurring at the R2 stage due to the high energy demands of the cowpea reproductive process. Our study highlights the importance of selecting cowpea genotypes with greater tolerance to waterlogging stress during the reproductive stage to mitigate the negative effects of waterlogging on seed yield in flood-prone environments. These results provide valuable insights into the mechanisms of cowpea's responses to waterlogging stress and can aid in developing strategies for improving cowpea yield in waterlogged environments, which are expected to become more frequent due to climate change.