Study of the physiological changes of Thomson Navel orange in response to foliar application of jasmonic acid under droght stress conditions

In order to evaluate the effects of different concentrations of jasmonic acid on the physiological changes of Thomson Navel orange under drought stress conditions, a factorial experiment was conducted based on a completely randomized design with three replications. The treatments consisted of three levels of drought stress 100% of field capacity (as control), 75% of field capacity (mild drought stress) and 50% of field capacity (severe drought stress) and three concentrations of jasmonic acid 0, 100 and 200 µM. The results showed that drought stress significantly reduced relative water content, plant water potential, leaf area index, stomatal conductance and total chlorophyll of Thomson Novel orange leaf, whereas ion leakage, malondialdehyde, soluble sugars, proline content and antioxidant enzyme activity increased under drought stress conditions. It was also found that foliar application of jasmonic acid was able to maintain the leaf water status (relative leaf water content and plant water potential), increase leaf area index, stomatal conductance, maintain cell membrane stability (by reducing ion and malondialdehyde leakage), maintain total chlorophyll at the optimal levels, increase the amount of compatible solutions (soluble sugars and proline) as well as increase the activity of catalase, superoxide dismutase, ascorbate peroxidase and peroxidase, therefore, reduce the negative effects of drought stress. Overall, the foliar application of jasmonic acid, especially at 100 μM concentration, is recommended to reduce the negative effects of drought stress on Thomson Novel oranges.