Role of Plant Genetic Resources and γ-Aminobutyric Acid (GABA) to Enhance Drought Tolerance of Cucumber (Cucumis sativus)

Cucumber is drought-sensitive vegetable. A considerable part of cucumber farming is carried out in arid and semiarid regions. In order to investigate the morpho-physiological responses of different Iranian cucumber accessions to γ-aminobutyric acid (GABA) foliar application under deficit irrigation strategy (DI), factorial split plot experiments were laid out during 2019–2021. The highest leaf area was recorded in Basmenj accession treated by GABA 40 mM under DI0% (194.99 cm2). Leaf soluble protein, free proline content and peroxidase and catalase enzymes activity increased with increasing GABA concentration. Water use efficiency increased by 46.94% in Kerkyneh accession under DI50% compared to Basmenj accession under DI0%. The highest stomatal conductance was observed in Basmenj accession under DI0% (601.33 mM m−2 s−1). The results of principal components analysis showed that 87% of observed variability was explained by first three components and first principal component explained 69% of total variability. In conclusion, Kerkyneh could be introduced as drought tolerant accession due to its suitable stomatal responses, high antioxidant capacity, high free proline content and suitable photosynthetic performance under drought stress conditions. GABA foliar application could improve drought tolerance of cucumber plant by increasing free proline content, peroxidase and catalase enzymes activity, photosynthetic rate and water use efficiency. Foliar application of GABA 40 mM could be introduced as useful technique to overcome adverse effects of drought stress on cucumber farming.