The majority of cowpea (Vigna unguiculata (L.) Walp.) produced in the U.S. is planted shortly after the summer rains and subsequently depends on rain or artificial irrigation. Therefore, excessive precipitation and poor soil drainage will cause cowpea plants to suffer temporary waterlogging, reducing the submerged tissue's oxygen level. Although cowpea is sensitive to waterlogging, excessive moisture can induce several morpho-physiological changes with adverse impacts on yield in its early stages of development. The current study subjected 30 cowpea genotypes to 10-days of waterlogging at the seedling stage under a controlled environment. The dynamic changes of 24 morpho-physiological parameters under waterlogging and optimal water conditions were analyzed to understand cowpea's response to waterlogging. Significant waterlogging treatment, cowpea genotypes, and their interactions (P < 0.001) were observed for most of the measured parameters. The results indicated that plant height (PH), leaf area (LA), fresh (FW) and dry weight (DW) of cowpea genotypes were significantly decreased under waterlogging compared to the control treatments. Similar results were obtained for net photosynthesis (P_n), stomatal conductance (g_s), intercellular CO₂ concentration (C_i), and transpiration rate (E). However, the water use efficiency (WUE) and adventitious roots (ARs) increased linearly under waterlogging conditions. Waterlogging also declined chlorophyll fluorescence parameters except non-photochemical quenching (qN), which increased with excess soil moisture. In addition, waterlogging tolerance coefficient (WTC) and multivariate analysis (MCA) methods were used to characterize cowpea genotypes for waterlogging tolerance. Accordingly, the cowpea genotype Dagupan Pangasinan, UCR 369, and Negro were classified as waterlogging tolerant, while EpicSelect.4 and ICARDA 140071, as the most waterlogging sensitive. The cowpea genotypes and morpho-physiological traits determined from this study may be useful for genetic engineering and breeding programs that integrate cowpea waterlogging tolerance.

Seed germination is the stage in which plants are most sensitive to abiotic stress, including salt stress (SS). SS affects plant growth and performance through ion toxicity, decreasing seed germination percentage and increasing the germination time. Several priming treatments were used to enhance germination under SS. The objectives of this study were (1) to identify priming treatments to shorten the emergence period, (2) to evaluate priming treatments against the SS, and (3) to induce synchronized seed germination. Salt-sensitive ‘Burpee Bibb’ lettuce seeds were treated with 0.05% potassium nitrate, 3 mM gibberellic acid, and distilled water. All the primed and non-primed seeds were subjected to 100 mM sodium chloride (NaCl) or 0 mM NaCl (control). The seven-day experiment, arranged in a complete randomized block design with four replications, was conducted in a growth chamber maintained with 16/8 h photoperiod (light/dark), 60% relative humidity, and a day/night temperature of 22/18 °C. The result indicated that hydro-primed (HP) seeds were better synchronized under SS. Similarly, fresh mass (FM) and dry mass (DM) of cotyledon, hypocotyl, and radicle were the highest in HP lettuce regardless of SS. Electrolyte leakage was the lowest in the HP lettuce, while other priming methods under SS increased membrane permeability, leading to osmotic stress and tissue damage. Overall, hydro-priming can be a good priming method for synchronizing germination and increasing FM and DM by creating the least osmotic stress and ion toxicity in lettuce under SS.

Salt stress (SS) refers to excessive soluble salt concentrations in the plant root zone. SS also causes cellular water deficits, ion toxicity, and oxidative stress in plants, all of which can cause growth inhibition, molecular damage, and even plant mortality. Lettuce (Lactuca sativa L.) has a threshold electrical conductivity of 1.3–2.0 dS/m. Thus, this research focused on physiological, morphological, and biochemical attributes in multiple lettuce genotypes under SS compared to plants grown under control conditions. The experiment was arranged in a randomized complete block design with four replications. One month after planting, the salt treatment was applied at the rate of 100 millimoles (mM). The 0 mM salt in water treatment was considered the control. A significant effect of SS on different morphological and physiological traits was observed in one-month-old lettuce plants. PI 212099, Buttercrunch-1, and PI 171676 were highly salt-tolerant. Genotypes with high salt tolerance usually had poor growth potential under control conditions. This suggests that the morphological and physiological response of 38 lettuce cultivars towards SS is genotype dependent. Identifying SS’s physiological, morphological, and biochemical attributes in lettuce may help plant-breeders develop salt-tolerant lettuce genotypes.

Waterlogging is an important environmental stress limiting the productivity of crops worldwide. Cowpea (Vigna unguiculata L.) is particularly sensitive to waterlogging stress during the reproductive stage, with a consequent decline in pod formation and yield. However, little is known about the critical processes underlying cowpea’s responses to waterlogging during the reproductive stage. Thus, we investigated the key parameters influencing carbon fixation, including stomatal conductance (g_s), intercellular CO₂ concentration, chlorophyll content, and chlorophyll fluorescence, of two cowpea genotypes with contrasting waterlogging tolerance. These closely related genotypes have starkly contrasting responses to waterlogging during and after 7 days of waterlogging stress (DOW). In the intolerant genotype (‘EpicSelect.4’), waterlogging resulted in a gradual loss of pigment and decreased photosynthetic capacity as a consequent decline in shoot biomass. On the other hand, the waterlogging-tolerant genotype (‘UCR 369’) maintained CO₂ assimilation rate (A), stomatal conductance (g_s), biomass, and chlorophyll content until 5 DOW. Moreover, there was a highly specific downregulation of the mesophyll conductance (g_m), maximum rate of Rubisco (V_cmax), and photosynthetic electron transport rate (J_max) as non-stomatal limiting factors decreasing A in EpicSelect.4. Exposure of EpicSelect.4 to 2 DOW resulted in the loss of PSII photochemistry by downregulating the PSII quantum yield (F_v/F_m), photochemical efficiency (Φ_PSII), and photochemical quenching (qP). In contrast, we found no substantial change in the photosynthesis and chlorophyll fluorescence of UCR 369 in the first 5 DOW. Instead, UCR 369 maintained biomass accumulation, chlorophyll content, and Rubisco activity, enabling the genotype to maintain nutrient absorption and photosynthesis during the early period of waterlogging. However, compared to the control, both cowpea genotypes could not fully recover their photosynthetic capacity after 7 DOW, with a more significant decline in EpicSelect.4. Overall, our findings suggest that the tolerant UCR 369 genotype maintains higher photosynthesis under waterlogging stress attributable to higher photochemical efficiency, Rubisco activity, and less stomatal restriction. After recovery, the incomplete recovery of A can be attributed to the reduced g_s caused by severe waterlogging damage in both genotypes. Thus, promoting the rapid recovery of stomata from waterlogging stress may be crucial for the complete restoration of carbon fixation in cowpeas during the reproductive stage.

Drought-induced reduction in crop growth and productivity can be compensated by increasing atmospheric carbon dioxide (CO₂), a significant contributor to climate change. Drought stress (DS) affects crops worldwide due to dwindling water resources and irregular rainfall patterns. The experiment was set up under a randomized complete block design within a three-by-two factorial arrangement. Six SPAR chambers represent three blocks (10 replications each), where each chamber has 30 pots in three rows. Each chamber was maintained with 30/22 (day/night) °C temperature, with either ambient (aCO₂; 420 ppm) or elevated CO₂ (eCO₂; 720 ppm) concentrations. This experiment was designed to address the impact of DS on the physiological and biochemical attributes and study how the eCO₂ helps alleviate the adversity of DS in basil. The study demonstrated that DS + eCO₂ application highly accelerated the decrease in all forms of carotene and xanthophylls. eCO₂ positively influenced and increased anthocyanin (Antho) and chlorophyll (LChl). eCO₂ supplementation increased LChl content in basil under DS. Furthermore, DS significantly impeded the photosynthetic system in plants by decreasing CO₂ availability and causing stomatal closure. Although eCO₂ did not increase net photosynthesis (Pn) activity, it decreased stomatal conductance (gs) and leaf transpiration rate (E) under DS, showing that eCO₂ can improve plant water use efficiency by lowering E and gs. Peroxidase and ascorbate activity were higher due to the eCO₂ supply to acclimate the basil under the DS condition. This study suggests that the combination of eCO₂ during DS positively impacts basil’s photosynthetic parameters and biochemical traits than aCO₂.