Synergistic Effects of Ethephon and Gibberellic Acid on the Growth of Rice Seedlings Grown under Field and Environmentally Controlled Conditions

Abstract

A B S T R A C T Improving early seedling growth is crucial for direct-seeding rice cultivation. In this study, field and laboratory experiments were conducted to determine the effects of Plant Growth Regulators (PGRs) such as gibberellic acid (GA3) and ethephon (ET) on the early growth of direct-seeded rice. Seeds were treated with the PGRs and pre-germinated at 30°C in the dark. For the field experiment, two Flooding Depth (FD) regimes were established during the growth period: 0 cm (drained condition) and 2 cm (flooded condition). Treatment of seeds with ET or GA3 alone promoted the growth of seedling organs compared to that of the control at both the FDs in some cases. However, combined application of ET and GA3 (ET+GA3) synergistically improved the growth of different seedling organs at both the FDs in most cases with slight exception: the coleoptile and mesocotyl plus coleoptile (mesocotyl+coleoptile) length were not different across the PGR treatments under drained condition. Further, the growth of the second node tiller was stimulated by the application of ET alone under drained conditions. The laboratory experiment revealed that ET+GA3 increased the growth rate of mesocotyl+coleoptile and that of the first leaf. These results suggest that the combined application of ET and GA3 might be useful for improving the growth performance of rice seedlings in the direct seeding method.