Assessment of the Potential of Bitter Melon (Momordica charantia) and Squash (Cucurbita pepo) as Rootstocks for Enhancing Drought Tolerance in Cucumber

Drought is one of the major abiotic stress factors limiting crop yield and quality, posing a significant threat to sensitive species like cucumber (Cucumis sativus L.). This study evaluated the potential of bitter melon (Momordica charantia cv. Nusret F1) and squash (Cucurbita pepo cv. Aygır F1) as rootstocks to improve drought-related performance in cucumber scions (Akıncı F1 and Baymali F1). Grafted and non-grafted plants were grown under two irrigation regimes for 21 days: well-watered control (100% field capacity) and a water-withholding drought treatment. Drought stress significantly reduced morphological parameters across most experimental groups. Under drought conditions, the Akıncı F1/Aygır F1 combination showed the highest proline accumulation. This biochemical response was accompanied by pronounced reductions in dry leaf and dry biomass. This pattern suggests that proline accumulation is more closely associated with stress severity than with growth maintenance under drought conditions. Conversely, the Baymali F1/Aygır F1 combination maintained relatively higher leaf dry weight under drought, suggesting better growth maintenance under drought. Plants grafted onto Nusret F1 generally produced the lowest biomass but showed enhanced proline synthesis, indicating a stronger stress response despite reduced growth. In conclusion, while Aygır F1 supports higher growth and biomass maintenance under well-watered conditions, drought responses are strongly influenced by scion-rootstock compatibility and distinct physiological strategies, highlighting the importance of distinguishing growth performance from biochemical stress indicators such as proline accumulation.