Jiban Krishna Biswas, Ho Ando, and
Ken-ichi Kakuda
Soil Sci.Plant Nutr. 47-1, 87-100 (2001)
Key Words: Anoxia-tolerant rice genotype, pH, seedling parameters, seedling establishment, volatile fatty acids.
Some of the rice genotypes were selected as anoxia-tolerant.
But when seeded directly in lowland soil, the seedling establishment of
these genotypes varied with the locations. It was assumed that volatile
fatty acids (VFA) like acetic, propionic or butyric acid might be one of
the factors that affected this phenomenon along with the pH level. Very
specific data related to the anoxia-tolerant genotypes, namely VFA and
pH interaction, should be analyzed to develop a variety or relevant cultural
practice for direct seeding lowland culture. Therefore three in vitro studies
were conducted to observe the effect of VFA on seedling growth of five
anoxia-tolerant rice genotypes (IR41996-50-2-1-3, IR50363-61-1-2-2, BR736-20-3-1,
RP1669-1529-4254, and Haenuki) under hypoxic conditions and two pH regimes
of 5 and 7. The concentrations used for acetic acid were 0, 4, 8 and 12
mM, for propionic acid 0, 1, 2, and 3 mM and for butyric acid 0, 2, 4,
and 6mM. The solutions for seedling growth were changed every two days
to minimize the fluctuation of the pH level. Seedlings were grown in a
sealed test tube at 30oC for 7 days in the dark. The nature and extent
of the genotype response varied with the types of VFA, their concentrations
and the pH levels. Based on the survival trend of the 1st leaf five genotypes
were divided into three groups for each VFA separately. First leaf
survival was not affected either by the acid concentration or by the pH
up to 4mM in the case of acetic acid and 2mM in the case of butyric acid
for all the groups. Propionic acid, which was assumed to be the most toxic
affected, group I (IR50363-61-2-2 and Haenuki) and group III (RP1669-1529-4254)
genotypes at around 1mM. But the mere presence of this acid affected the
1st leaf survival of group II (BR736-20-3-1) genotype. The change of pH
from 5 to 7 led to the increase of the percentage of 1st leaf survival
for some genotypes at higher acid concentrations. However, irrespective
of the pH values (5 or 7), genotypes with a high 1st leaf survival at high
acid concentrations were also observed. The estimated concentration
of the VFA required for 80 percent survival of the 1st leaf depended on
the VFA itself and pH level. Seedling parameters were also influenced
by pH7 at higher VFA concentrations.