Enhancing pepper resilience to tebucanozole stress: role of copper and Bacillus subtilis microorganisms

Background: In this study, 75 and 100 ppm tebuconazole was applied to pepper seedlings and stress was created. Applications containing Bacillus subtilis, copper and Bacillus subtilis-copper combination were made to reduce the effect of stress on plants. Results: In both tebuconazole doses, significant decreases were observed in plant height, stem diameter, leaf number, leaf area and dry and fresh weights of plants and roots (63%, 37%, 40%, 45%, 27% and 26% respectively). However, bacteria, copper, and combination applications significantly reduced these negative effects; especially, copper-bacteria combination at 75 ppm (K4) and bacteria-only application at 100 ppm (K6) were the most effective in reducing stress. Tebuconazole applications increased oxidative stress and significant increases were detected in catalase (CAT) and superoxide dismutase (SOD) enzyme activities. The highest CAT activity was recorded in the group treated with bacteria (K6) under 100 ppm stress, indicating that antioxidant defenses were strengthened. Photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll and carotenoids) were decreased by tebuconazole stress but were significantly preserved by bacterial and copper treatments. While EC (electrolyte conductivity) value increased due to stress, bacteria and copper applications had a positive effect by decreasing EC values. While tebuconazole stress disrupted the balance of some elements, mineral levels were rebalanced after ameliorative applications, and increases were determined in important elements such as Mn, Mg and B. According to the correlation analysis, significant positive correlations were determined between growth parameters, pigment contents and antioxidant enzyme activities. Conclusions: As a result, Bacillus subtilis and copper applications provided a decrease in toxicity due to stress and increased antioxidant enzyme activity. In addition, ameliorative applications provided protection in photosynthetic pigments and increased cell membrane integrity. These findings indicate that the use of beneficial bacteria such as Bacillus subtilis and micronutrients such as copper (Cu) at appropriate concentrations may be beneficial as sustainable solutions against fungicide stress. © The Author(s) 2026.