Exogenous application of L-proline for inducing drought tolerance in lowland rice (Oryza sativa L.)

The effect of exogenous L-proline application for inducing drought tolerance in PSB Rc14 and PSB Rc82 under short-duration drought at different crop stages was evaluated based on shoot and yield parameters. Drought impositions were carried out for 10 days starting from water withdrawal during early vegetative (EV), panicle initiation (PI) and heading. Three experiments were conducted such as monitoring of drought occurrence, endogenous proline analysis, and efficacy evaluation of exogenous 1-proline application. The first experiment showed that a 10-day drought resulted to water deficit stress during PI and heading but was too short to cause drought stress during EV stage. The second experiment revealed that proline was normally at high levels and that no significant differences existed between flooded and drought conditions due to non-attainment of drought stress during EV stage. During PI and heading however, PSB Rc82 was highly sensitive to changes in soil water potential (SWP) which immediately triggers proline accumulation as a defense mechanism to an imminent drought. The proline levels of PSB Rc14 in both flooded and drought conditions remained constant at high levels, relative to that of PSB Rc82, thus providing an explanation for its adaptability under rainfed conditions. The third experiment showed that exogenous L-proline application on PSB Rc14 resulted to yield increments of 14-35% against without L-proline application under non-drought stress conditions. Exogenous L-proline application under drought conditions at PI and heading had no significant effect on yield. For PSB Rc82 however, exogenous L-proline application on drought-affected plants during EV and PI stages effectively produced similar yield levels with the non-drought-stress plants. Yield advantages over the drought-affected plants without proline application were 40% at EV and 78% at PI. Hence, this study confirms that proline as an osmoregulant for rice under drought conditions can be substituted through exogenous application to maintain normal yield levels.