Differences in the rate of seedling emergence among rice cultivars under low soil-moisture conditions

The objective of this study was to identify rice cultivars with high emergence ability under low soil-moisture conditions using a large number of rice cultivars, and to clarify the differences between the rates of emergence in lowland and upland, white- and red-kerneled, and non-glutinous and glutinous cultivars. First, 30 cultivars with a high emergence rate at 14 days after sowing (DAS) were selected at a soil water potential of -1.17 to -0.89 MPa from 382 cultivars through four screening experiments. In these experiments, the emergence rate was significantly higher in the upland cultivars than in the lowland cultivars. The red-kerneled cultivars also had a significantly higher emergence rate than the white-kerneled cultivars. However, no difference in emergence rate was observed between the non-glutinous and glutinous cultivars. Second, the emergence rates of various cultivars were examined at a soil water potential of -1.62, -1.23, and -1.07 MPa. The higher the soil water potential, the higher the emergence rate at 28 DAS and the shorter the time to the emergence. The order of cultivars in their emergence rate at 13 DAS at -1.07 MPa was similar to that at 28 DAS at -1.62 MPa. Therefore, the data at 13 DAS at -1.07 MPa were used to compare the selected 30 cultivars for their emergence ability under low soil-moisture conditions. Moulla Topa showed the highest emergence rate (78.1%) and Gaiya Rate Bhasunamathe the shortest time to 50% emergence (11.1 d) under these conditions.