Water stress is the most critical aspect restricting the development of agriculture in regions with scarce water resources, which requires enhancing irrigation water-saving strategies. The current work discusses the potential application of the plant-strengthening root endophyte Piriformospora indica against moderate (25% less irrigation water) and severe (50% less irrigation water) water stress in comparison to the optimum irrigation conditions of greenhouse cucumbers. P. indica improved growth, nutrient content, and photosynthesis apparatus under normal or water-stress conditions. On the other hand, moderate and severe water stress reduced yield up to 47% and 83%, respectively, in non-colonized cucumber plants, while up to 28 and 78%, respectively, in P. indica-colonized plants. In terms of water-use efficiency (WUE), P. indica improved the WUE of colonized cucumber plants grown under moderate (26 L/kg) or severe stress (73 L/kg) by supporting colonized plants in producing higher yield per unit volume of water consumed by the crop in comparison to non-colonized plants under the same level of moderate (43 L/kg) or severe (81 L/kg) water stress. Furthermore, P. indica increased the indole-3-acetic acid (IAA) content, activity levels of catalase (CAT) and peroxidase (POD) with an apparent clear reduction in the abscisic acid (ABA), ethylene, malondialdehyde (MDA), proline contents and stomatal closure compared to non-stressed plants under both water-stress levels. In addition, chlorophyll a, b, a + b contents were increased in the leaves of the colonized plants under water-stress conditions. This improvement in chlorophyll content could be correlated with a significant increment in the transcripts of chlorophyll biosynthesis genes (protochlorophyllide oxidoreductase [POR], chlorophyll a oxygenase [CAO]) and a reduction in the chlorophyll degradation genes (PPH, pheophorbide a oxygenase [PAO], and red chlorophyll catabolite reductase [RCCR]). In conclusion, P. indica has the potential to enhance the cucumber yield grown under moderate water stress rather than severe water stress by improving WUE and altering the activity levels of antioxidant enzymes and chlorophyll metabolism-related genes.

Cowpea is a high-protein legume. Water stress is the most significant obstacle that hinders agriculture development in regions with limited water resources. Drought stress affects cowpea production, i.e., growth, yield and quality. An experiment was conducted to evaluate some cowpea accessions for drought tolerance at reproductive stage and studying the physiological, molecular and anatomical basis of tolerance. Six accessions were selected from a previous investigation to study the nature of drought tolerance at reproductive stage. Accessions TVU-14997, TVU-15304 and TVU-15306 exhibited high drought tolerance based on their high levels of each of antioxidant capacity, total phenols, catalase, peroxidase and abscisic acid during reproductive stage. The molecular study using specific primers confirmed the agronomical findings. The identification of potential genetic markers associated with drought tolerance in this study is a promising avenue for future research. The development of molecular markers for drought tolerance can facilitate marker-assisted selection in breeding programs, accelerating the development of drought-tolerant cowpea varieties. Regarding anatomical structure, under drought condition, accession TVU-15306 had the highest value for thickness of the midvein, spongy tissue, dimension of vascular bundle and mean vessels diameter. Water stress was found to negatively affect growth of studied cowpea accessions. Results showed that accessions TVU-14997, TVU-15304 and TVU-15306 were drought tolerant as evidenced by high levels of each of antioxidant capacity, total phenols, catalase, peroxidase and abscisic acid. They can be used as sources of tolerance to drought stress in breeding programs.