To evaluate the interaction between foliar application of salicylic acid and Bradyrhizobium inoculation on the morphophysiology of cowpea under water stress conditions, four genotypes (BRS Rouxinol, BRS Marataoã, BRS Aracê and BR 17 Gurguéia) were subjected to five combinations of water availability: 100% replacement of crop evapotranspiration (control); 50% replacement of crop evapotranspiration (water stress); water stress + salicylic acid; water stress + Bradyrhizobium inoculation; and water stress + salicylic acid + Bradyrhizobium inoculation. The experiment was set up in a 4 × 5 factorial randomized block design, with four replicates and four plants per plot. Water stress negatively affected the leaf water potential, growth, proline contents and antioxidant activity of the cowpea genotypes, and BRS Marataoã was the most sensitive. Under water stress conditions, Bradyrhizobium inoculation was efficient for BRS Rouxinol, but was only efficient for BRS Marataoã, BRS Aracê and BR 17 Gurguéia when associated with foliar application of salicylic acid, maintaining their values of leaf water potential, growth, proline content and activities of superoxide dismutase, ascorbate peroxidase, and catalase similar to those of the control treatment.

Exogenous applications of chemical compounds stimulate changes in plant metabolism and promote tolerance to different environmental stresses, including water deficit. This study aimed to evaluate the ability of salicylic acid (SA) and proline (PRO) to reduce water stress in a traditional variety of cowpea in a typical Brazilian semiarid climate. A completely randomized design was used in a 2 × 4 factorial scheme, with five replicates. Two irrigation regimes were evaluated corresponding to 100% (W100) and 50% of daily evapotranspiration (W50), respectively, with the addition of the following four attenuators: control (distilled water), SA (550 mg L-1), PRO (690 mg L-1), and 690 mg L-1 PRO + 550 mg L-1 SA. The treatments promoted changes in osmotic and antioxidant metabolism, which may contribute to the tolerance mechanisms of cowpea plants to water stress. The application of SA increased osmoregulator synthesis and protein concentrations, and modulated antioxidant enzyme activity in the cowpea plants under water stress. PRO concentrations increased synergistically in plants treated with PRO and SA, particularly in 50% of water replacement.

Global climate changes have intensified water stress in arid and semi-arid regions, reducing plant growth and yield. In this scenario, the present study aimed to evaluate the mitigating action of salicylic acid and methionine in cowpea cultivars under water restriction conditions. An experiment was conducted in a completely randomized design with treatments set up in a 2 × 5 factorial arrangement corresponding to two cowpea cultivars (BRS Novaera and BRS Pajeú) and five treatments of water replenishment, salicylic acid, and methionine. After eight days, water stress decreased the Ψw, leaf area, and fresh mass and increased the total soluble sugars and catalase activity in the two cultivars. After sixteen days, water stress increased the activity of the superoxide dismutase and ascorbate peroxidase enzymes and decreased the total soluble sugars content and catalase activity of BRS Pajeú plants. This stress response was intensified in the BRS Pajeú plants sprayed with salicylic acid and the BRS Novaera plants with salicylic acid or methionine. BRS Pajeú is more tolerant to water stress than BRS Novaera; therefore, the regulations induced by the isolated application of salicylic acid and methionine were more intense in BRS Novaera, stimulating the tolerance mechanism of this cultivar to water stress.

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