Evaluation of low temperature tolerance indices in seedlings of Citrus aurantium under potassium nitrate nutrition.

In order to evaluate the effects of potassium nitrate nutrition on some low temperature tolerance indices in Citrus aurantium seedlings a factorial experiment was conducted based on a completely randomized design with four replications at the Institute of Citrus Research in Ramsar. Treatments were potassium nitrate nutrition at four levels (0, 2.5, 5, and 10 mM) and temperature at four levels (25, 0, -3, and -6 °C). Results showed that increasing the concentration of KNO3 reduced superoxide dismutase activity and carotenoid. Concentration of 10 mM potassium nitrate also increased water content, leaf color, proline, phenol, and total chlorophyll. Maximum leaf damage, electrolyte leakage, and carotenoid were observed at -6 °C, while the highest antioxidant capacity and superoxide dismutase activity with means 37.7% and 24.4 IU. mg -1 FW, respectively were observed in Citrus aurantiumleaves at -3 °C. Highest electrolyte leakage was observed at concentration 0 mM potassium nitrate and temperature of -6 °C while highest superoxide dismutase was observed at -3 °C with the same concentration of potassium nitrate. Results revealed that concentration of 10 mM potassium nitrate increases Citrus aurantium tolerance under low temperature stress.