Evaluation of Physiological and Biochemical Responses of Four Tomato (<i>Solanum lycopersicum</i> L.) Cultivars at Different Drought Stress Levels

Drought, one of the abiotic stress factors that threatens world food security, destructively limits the growth and development of agricultural plants. Therefore, determining drought-resistant cultivars is of vital importance against increasing climate change. Tomato (<i>Solanum lycopersicum</i> L.) is one of the most important economic agricultural plants grown worldwide. In this study, different drought stress tolerances (10% PEG (Polyethylene Glycol 6000) and water scarcity) were applied to four commercial tomato cultivars (Rio Grande, Falcon, H−2274, Tyfrane F1) and the effects of drought stress were evaluated within the scope of physiological (germination percentage, shoot length, root length, fresh weight, dry weight, total chlorophyll content, relative water content) and biochemical (protein amount, superoxide dismutase (SOD), peroxidase activity (POX), catalase activity (CAT), hydrogen peroxide content (H₂O₂) and lipid peroxidation activity (TBARs)) parameters. According to the research results, it was determined that drought stress leads to decreased root–shoot lengths, chlorophyll content, relative water content, fresh and dry weights, and antioxidant enzyme activities in Falcon and H−2274 cultures, increasing TBARs and H₂O₂ amounts. While the relative water content, which is an indicator of drought stress, shows the water status of the plant, antioxidant enzyme systems are evidence of the resilience of the defense mechanisms of the cultures. In this context, the Falcon cultivar had significantly reduced shoot length (21%, 37%), relative water content (20%, 30%), chlorophyll content (7%, 23%), fresh weight (51%, 49%) and dry weight (9%, 29%) under PEG and water scarcity application; in contrast to these reductions, TBARs (2%, 14%) and H₂O₂ content (3%, 15%) were significantly increased compared to the control, proving that it is a susceptible cultivar. On the other hand, a slight decrease in relative water content (1%, 3%), a slight increase in total chlorophyll content (6%), intense CAT activity (50%, 67%) and SOD activity (30%), but a decrease in lipid peroxidation level (5%, 22%) and a decrease in H₂O₂ content (11%, 15%), were detected in the Rio Grande cultivar in PEG and water scarcity treatment compared to the control, proving that this cultivar is resistant to drought and can be effectively grown in water-scarce areas. It was determined that four tomato cultivars had different perception and antioxidant defense systems against drought stress. As a result, when four tomato cultivars under different drought stress levels were evaluated in terms of physiological and biochemical parameters, the tolerance levels were determined as Rio Grande > Tyfrane F1 ≈ Tyfrane F1 > H−2274 > Falcon. In this context, the different responses of tomato cultivars to PEG and water scarcity are important for the selection of drought-resistant cultivars and the development of strategies to increase plant productivity under abiotic stress conditions.