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 seede d directly in lowland soil, the seedling establishment of these genotypes v aried with the locations. It was assumed that volatile fatty acids (VFA) li ke acetic, propionic, or butyric acid might be one of the factors that affe cted this phenomenon along with the pH level. Very specific data related to the anoxia-tolerant genotypes, namely VFA and pH interaction, should be an alyzed to develop a variety or relevant cultural practice for direct seedin g lowland culture. Therefore three in vitro studies were conducted to obser ve the effect of VFA on seedling growth of five anoxia-tolerant rice genoty pes (IR41996-50-2-1-3, IR50363-61-1-2-2, BR736-20-3-1, RP1669-1529-4254, an d Haenuki) under hypoxic conditions and two pH regimes of 5 and 7. The conc entrations 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 f or 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 th e types of VFA, their concentrations and the pH levels. Based on the surviv al trend of the first leaf five genotypes were divided into three groups fo r each VFA separately. First leaf survival was not affected either by the a cid 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 Ha enuki) and group III (RP1669-1529-4254) genotypes at around 1 mM. But the m ere presence of this acid affected the first leaf survival of group II (BR7 36-20-3-1) genotype. The change of pH from 5 to 7 led to the increase of th e percentage of first leaf survival for some genotypes at higher acid conce ntrations. 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 fir st leaf depended on the VFA itself and pH level. Seedling parameters were a lso influenced by pH 7 at higher VFA concentrations.