Some Factors Affecting the Emergence and Establishment of Rice Seedlings (Oryza sativa L.)

To examine the factors affecting the emergence and establishment of rice seedlings, we tested FAO-designated germ plasm 207 cultivars (indica rice 137 cultivars, japonica rice 56 cultivars, and unexplained ecospecies 14 cultivars) collected from throughout the world. In the first experiment, the seeds were sown in nursery soil at a seeding depth of 3.0cm. Seeded pots were kept in a greenhouse at 30/25°C for 21 days. The ratio of the established plants (REP) to total plants was measured at 21 days after seeding. As a result, 13 cultivars, 6.3% of the total tested showed the best REP, i.e., 100-80%. These include 7 indica types and 6 japonica types of rice. In the second experiment, 75 cultivars were selected as the materials. The plants were grown under the same conditions as the first experiment, but the seeding depths were 1.0 and 3.0 cm. The chlorophyll contents of the second leaf blades and REP were measured at 2 and 3 weeks after seeding, respectively. The REP showed no correlation to seed weight, whereas correlation existed between REP and the values of chlorophyll contents of the second leaf blades at 1 cm and 3 cm seeding depths 2 weeks after seeding. In conclusion, seedling establishment seemed to be affected by the rate of increase in the chlorophyll contents of the leaves.