Abstract
Twenty Japonica and 13 Indica cultivars of rice were seeded on the soil surface in paddy field and at a 1 cm depth in the soil and the soil surface in a container, and the type of their seedling establishment was examined. The seedling-establishment type was determined at the 3rd leaf stage as follows. Perfect establishment type (PE) : seedlings emerge from soil ; Fixed type (FX) : seedlings are fixed although a part of the roots emerge above the ground ; Floating-1 type (FL-1) : seedlings are fixed although the seed are floating ; Floating-2 type (FL-2) : seedlings are floating. After the soil-surface seeding, the percentage of FX, FL-1 and FL-2 was 20-60%, 10-35% and 24-55%, respectively, in most cultivars. The percentage of floating type (FL-1 and FL-2) in paddy field positively correlated with that in the container when seeded on the soil surface. The percentage of floating type in the seed sown on the soil surface positively correlated with that in the seed sown at a 1 cm depth in soil in the container. Moreover, the percentage of floating type in the soil-surface seeded rice in the container negatively correlated with the total root length and root dry weight, and positively correlated with the (plant length)/(total root length) ratio and top/root ratio. The percentage of floating type was relatively low when root growth was vigorous, and it positively correlated with the (seminal root length)/(total root length) ratio. The development of adventitious roots following the elongation of the seminal root was found to be important for seedling establishment.
