Abstract
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.
Highlights
Cucumber is one of the main protected culture crops grown in the Mediterranean region because it has potential health benefits and is quite well adapted to grow under different protected culture conditions [1,2,3]
Water stress significantly decreased plant height, plant fresh weight, and average leaf area in colonized or non-colonized cucumber plants when subjected to 25% (W-25, as moderate stress) and 50% (W-50, as severe stress) reduction in irrigation water (Figure 2A–C)
Colonizing cucumber with P. indica improved the above growth traits under normal or stress conditions compared to non-colonized plants
Summary
Cucumber is one of the main protected culture crops grown in the Mediterranean region because it has potential health benefits and is quite well adapted to grow under different protected culture conditions [1,2,3]. Horticulturae 2021, 7, 399 rapidly expanded worldwide, together with demanding new strategies to solve specific biotic and abiotic stress-limiting production factors [4,5,6,7]. The current work aims to study the potential of P. indica utilization on greenhouse cucumber plants grown under three irrigation levels to improve plant growth, production, and resistance to irrigation water stress. In this respect, morphophysiological traits, photosynthetic activity, hormone quantification, the activity levels of antioxidant enzymes, and specific chlorophyll metabolism related genes were evaluated under normal irrigation and moderate and severe water-stress conditions
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