Effect of manganese applications on growth and physiological responses of pepper (Capsicum annuum L. 'Mazamort') under different drought stress levels

Pepper (Capsicum annuum L.), a widely cultivated and economically important crop, is particularly sensitive to drought stress. Recent studies have suggested that micronutrient applications, such as manganese, may play a role in mitigating the adverse effects of drought by enhancing plant stress tolerance. This study aimed to evaluate the effects of different manganese concentrations on the growth and physiological responses of the commercial pepper cultivar 'Mazamort' under varying levels of drought stress. The experiment was conducted under controlled climate chamber conditions with 60–65% relative humidity, 8000 lux light intensity, and a 16/8 h light/dark photoperiod at 24±1°C and 18±1°C. Plants were grown in 2-liter pots filled with a 2:1 peat-perlite mixture. Treatments included: 100% irrigation, 50% and 25% drought stress, and manganese applications at 2.5 mg L-1 and 5 mg L-1, applied alone or in combination with each drought level. Parameters measured included plant height, stem diameter, leaf and branch number, fresh and dry weights of shoot and root, water content, SPAD value, root water status, relative water content (RWC), turgor loss, and ion leakage. Drought stress significantly reduced plant growth and physiological performance. The highest plant height (73.50 cm), SPAD value (44.37), and fresh weight (49.80 g) were observed in the control or control+Mn treatments, whereas the lowest values were generally recorded in the 25% drought+2.5 or 5 mg L-1 Mn treatments. The most severe turgor loss (21%) and ion leakage (23.54%) occurred under 25% drought stress, especially when combined with Mn application, indicating increased cellular damage. RWC was highest (88.78%) in the control and lowest (76.52%) under severe drought. In conclusion, different concentrations of manganese were found to be insufficient in mitigating the adverse effects of severe drought stress on growth and physiological parameters in the Mazamort pepper cultivar.