Effects of Biostimulants on Alleviating Drought Stress in Isparta Rose

Abstract

Drought stress is one of the major abiotic factors limiting the growth and productivity of Rosa damascena. This study aimed to evaluate the effects of different biostimulant applications on the antioxidant defense system and biochemical responses of R. damascena under varying irrigation levels. Plants were grown under three irrigation regimes (100%, 50%, and 25% of field capacity (FC)) for 28 days, and treatments included vermicompost extract (V), Bacillus OSU-142 (B), and an algal extract (A) collected from Eğirdir Lake. Antioxidant enzyme activities, oxidative stress markers (MDA, H₂O₂), and proline content were measured weekly. Results showed that decreasing irrigation levels induced significant increases in antioxidant enzyme activities, MDA, H₂O₂, and proline content, indicating oxidative and osmotic stress responses. Under well-watered conditions (100% FC), biostimulant applications had limited effects on these parameters. However, under moderate (50% FC) and severe drought stress (25% FC), biostimulant treatments effectively reduced MDA, H₂O₂, and proline accumulation, and led to lower antioxidant enzyme activities compared to controls. Bacillus OSU-142 and vermicompost were particularly effective treatments in mitigating oxidative damage and maintaining cellular homeostasis under severe water deficit. These findings show that biostimulants reduce ROS accumulation and lipid peroxidation while modulating antioxidant defense in R. damascena.