Plant Stress (Dec 2021)
Varying drought stress induces morpho-physiological changes in cowpea (Vigna unguiculata (L.) genotypes inoculated with Bradyrhizobium japonicum
Abstract
Increased environmental fluctuations because of climate change have been forecasted in many agricultural regions to increase the frequency, intensity, and duration of drought episodes, which threaten the sustainability of future crop production. Although cowpeas are drought-tolerant, recent evidence shows that soil water stress in the early stages of vegetative growth significantly impairs crop growth and development, with detrimental impacts on yields. Diversity in cowpeas has been extensively genotyped and sequenced to enhance drought stress tolerance based on genetic diversity, population structure, and phylogenetic relationships. Hence, this study was conducted to evaluate whether cowpea genotypes with contrasting drought-tolerant status respond differently to varying moisture stress under a controlled environment. Three cowpea genotypes, including Arkansas Blackeye #1 (ARB), Top Pick Cream (TPC), and 17–111 were subjected to 28 days of three volumetric water content (VWC) treatments, which comprised of 0.270, 0.203, and 0.135 m3m−3, identified respectively as well-watered (WW), intermediate drought (ID), and drought-stressed (DS) conditions. After 28 days of VWC treatment (DAT), it was observed that the seedlings of all cowpea genotypes survived, showing different characteristics of the DS effect. The results showed that plant height (PH), leaf area (LA) and number (LN), fresh (FM) and total dry mass (TDM) of cowpea genotypes were significantly decreased under DS compared to WW and ID. Furthermore, cowpea genotypes subjected to DS showed significant reductions in their rate of photosynthesis (Pn) at 14 DAT when compared to 28 DAT. Thus, suggesting cowpeas tend to adapt to DS with time. Similar results were obtained for stomatal conductance (gs), intercellular CO2 concentration (Ci), and transpiration rate (E). However, the water use efficiency (WUE) increases linearly under DS. DS also resulted in the decline of chlorophyll fluorescence parameters except non-photochemical quenching (qN) which increased with decreasing VWC treatments. Overall, the ARB was observed to have significantly highest Pn, gs, E, Ci, LA, PH, Jmax, and Vcmax at DS, ID, and WW when compared to TPC and 17–111 cowpea genotypes, indicating its tolerance to DS. Cowpea breeders may use the contrasting drought-tolerant genotypes and identified morpho-physiological features to develop new genotypes that could tolerate DS during the vegetative stage in future climates.
