J.K.Biswas, H,Ando, and K.Kakuda
Key words: Anaerobic seeding, coleoptile, first leaf, rice, seedling establishment
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 sothe il. Further analysis of 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 day-night temperature of 30oC 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 mgL-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.