Seedling establishment of anoxia-tolerant rice (Oryza sativa L.) as affected by anaerobic seeding in two different soils

Abstract

Anaerobic seeding of an anoxia-tolerant rice genotype should be more convenient than the application of other methods. However, in this kind of genotype, seedling establishment also varies from due to area. The nature and properties of soil may influence the intensity of stress developed within the flooded soil. Further analysis of the behavior of the seedling organs under varying levels of stresses in submerged soils is required for the development of anaerobic seeding technology. Sprouted seeds from 14 rice genotypes were sown in submerged soils from upland and lowland areas, and allowed to grow in a phytotron at a daynight temperature of 30°C for 10 d. After 24 h of submergence, the level of dissolved oxygen in the upland and lowland soils were 4.4 and 0.5 mg L⁻¹, respectively. In the soils from a lowland area in some genotypes, the coleoptiles were hardly able to reach the oxygenated soil-water transition layer, resulting in a poor seedling establishment. Although the coleoptile laws longer than the soil-covering depth, some genotypes showed a poor seedling establishment in the same soil. It appeared that the growth of the first leaf length was affected by the accumulation of anaerobic toxic products from the highly reduced lowland soil. The elongated coleoptile is considered to supply oxygen to the growing region of the seedling for the initiation of the growth of the first leaf. The first leaf should therefore, be able to tolerate the anaerobic toxins. As a result, it is assumed that a mechanism of avoidance (by elongated coleoptile) and a mechanism of tolerance (by first leaf survival) are required for seedling establishment in highly reduced soil. As in upland soil the stress appeared to be relatively low, coleoptile alone was able to support the formation of the first leaf through oxygen transport to the growing region, i.e. through an avoidance mechanism.

Key Words:

• anaerobic seeding
• coleoptile
• first leaf
• rice
• seedling establishment