The use of biostimulants is one of the recognized strategies for mitigating the adverse effects of drought on crops. In a greenhouse tomato experiment, the effect of two biostimulants in combination with three levels of drought was investigated. Specifically, the doses of 150 mL and 1000 g ha⁻¹ of a plant-derived polyhydroxy acids extract (B1) and a Sargassum seaweed extract (B2), respectively, were studied in combination with drought levels of 85, 63.75, and 42.5% of field capacity. Four applications were performed during key growth stages. The effects were comprehensively investigated by assessing agronomic and physiological traits of the plants at three defined time points during the experimental period. Furthermore, organoleptic characteristics, bioactive compounds, antioxidant activity in the fruits, and overall yield components were evaluated. Drought stress provoked a consistent negative impact on several physiological traits, such as stomatal conductance (up to −58.3%), net photosynthesis (up to −47.9%), and quantum yield. A comparable impact was observed on agronomic traits, such as plant height, stem thickness, and number of leaves, with reductions of up to 13.6%. Both biostimulants’ applications enhanced certain physiological features across all irrigation levels, including net photosynthesis by up to 44.3% and chlorophyll content index by up to 33.4%, while B2 further increased intrinsic water use efficiency by up to 42.9% compared to the respective controls. However, this trend was not reflected in the evaluated post-harvest parameters, such as fruit yield, fruit number, fruit weight, and quality indices. These findings suggest that biostimulants may have a supporting role in physiological responses under drought stress but have limited effects on fruit production. Future research should focus on optimizing the formulation, dosage, and timing of biostimulant applications, as these factors may be critical to enhancing plant tolerance to drought stress and improving fruit yield responses.

Drought stress is a major constraint in eggplant cultivation, limiting growth, physiological performance and yield. Solanum relatives may provide alleles for improving drought tolerance. The objective of this study was to evaluate the responses of cultivated, wild and interspecific eggplant genotypes under water stress to identify drought-tolerant genotypes. Four-week-old plants of three Greek eggplant cultivars—S. macrocarpon (cultivated), S. dasyphyllum (wild), and three S. melongena × S. dasyphyllum hybrids—were grown under full and deficit irrigation and assessed for 10 agronomic and 7 physiological traits. Genotype, irrigation level and their interaction significantly affected most traits. Eggplant showed greater sensitivity under water stress with reductions in 9 agronomical traits, such as leaf number (12.9–15.8%), plant height (15.4–25.1%), LAI (47.7–55.4%), root (32.1–46.6%) and plant biomass (31.4–38.6%). S. dasyphyllum and S. macrocarpon maintained relative growth and physiological stability through different mechanisms, indicating enhanced drought tolerance. S. dasyphyllum exhibited reduction only in leaf number (11.5%), plant height (17.8) and LAI (23.9%), while S. macrocarpon exhibited reduction only in leaf length (18.1%) and LAI (55.0%). Interspecific hybrids displayed intermediate responses and heterosis under control (−22.2 to 66.6%) and stress (−29.8 to 81.5%) conditions. These findings support the use of wild or cultivated germplasm in breeding drought-resilient eggplant cultivars and rootstocks and enhancing crop sustainability.