Effect of volatile fatty acids on seedling growth of anoxia-tolerant rice (Oryza sativa L.) genotypes

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 6 mw. The solutions for seedling growth were changed every 2d to minimize the fluctuation of the pH level. Seedlings were grown in a sealed test tube at 30 degreesC for 7d 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 first 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 4 mill in the case of acetic acid and 2 mM in the case of butyric acid for all the groups. Propionic acid, which was assumed to be the most toxic affected, group I (IR50363-61-1-2-2 and Haenuki) and group III (RP1669-1529-4254) genotypes at around 1 mM. But the mere presence of this acid affected the first 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 first leaf survival for some genotypes at higher acid concentrations. However, irrespective of the pH values (5 or 7), genotypes with a high first leaf survival at high acid concentrations were also observed. The estimated concentration of the VFA required for 80% survival of the first leaf depended on the VFA itself and pH level. Seedling parameters were also influenced by pH 7 at higher VFA concentrations.