Acronyms and Glossary of Rice Related Terminology Updated November 27, 2002

O Terms

obcordate. An inverted heart shape.

objective. Goal or purpose. In research, it is usually testing of hypothesis within the experimental framework.

oblanceolate. Lanceolate, but with the widest part toward the apex.

obligate. An organism that can sustain life only when thriving in another living organism.

obligate parasite. A parasite that in nature can grow and multiply only under specific conditions such as on or in living organisms.

oblique. Sloping, having unequal sides (leaves).

oblong. Longer than broad with almost-parallel sides.

obovate. Ovate, but the widest part toward the apex.

obovoid. An inverted egg shape.

observation. Record of the facts and information in a sequence of events exactly, during the research program.

observation well. A perforated pipe inserted into the soil to record the level of the water table in relation to the soil surface.

observation yield trial. A preliminary yield trial with small plots, often unreplicated.

obsolete types. Varieties of rice that are considered of no importance at present or no longer popular and used by the community.

obtuse. Blunt or rounded at the end.

off-season crop. A crop that is planted after the main planting season has been completed.

off-shoot. A lateral branch of the plant that may not be propagated.

off-types. Plant that differ in morpho-agronomic characters from the majority or representative plants of a variety; admixtures in a field; obvious contaminants such as tall plants in a semidwarf cultivar or vice versa.

oligogene. A gene controlling the inheritance of a qualitative character or one showing typical Mendelian distribution.

oligogenic resistance. Resistance governed by a few genes. Major gene resistance.

oligonucleotide. A polymer of nucleotides usually 5-30 base pairs long.

oligophagous. Eating only a few specific kinds of food - used especially for an insect subsisting on a few usually related plants.

on-farm trial/on-farm research. Experiment conducted in farmers' fields.

once-over tillage. An operation whereby land is tilled and planted in the same operation.

ontogeny. The sum of individual morphogenic processes and event, that describe plant development from seed germination through maturity.

open hull. The lemma and hull cannot close after opening at blooming time.

opaque. Impervious to the rays of visible light: not transparent or translucent, e.g., the glutinous endosperm of the rice grain.

open pollination. The natural process of pollinating grains in a plant (not controlled).

operon. A cluster of functionally related genes regulated and transcribed as a unit.

optimum tillage. The combination of tillage operations which maximizes growth of crop plants.

optimum photoperiod. The day length at which growth duration is at a minimum.

orange leaf. A disease caused by a mycoplasmalike organism. The causal agent is restricted in the cells of the phloem sieve tubes and is vectored by leafhoppers. The disease is characterized by short, malformed leaves, the edges of leaves are serrated and chlorotic, and the leaf tips are twisted. At the later stage, the leaves turn yellow-orange beginning at the tip. Leaves may become entirely orange, roll inward and dry out.

orbicular. Almost circular.

organ. A functionally distinct part of an organism consisting of several kinds of tissues such as leaf, root, flower, seed, etc.

organelle. Membrane-bound cellular compartment (e.g., nucleus, chloroplast, mitochondrion, Golgi apparatus).

organic. Of, relating to, or derived from living organisms. Being composed of or containing matter of plant and animal origin.

organic fertilizers. Fertilizer materials derived from plant and animal parts or residues.

organic matter. The fraction of the soil that includes plant and animal residues at various stages of decomposition and substances synthesized by the soil populations of various organisms.

organic phosphorus. Phosphorus present as a constituent of an organic compound, or a group of organic compounds such as glycerophosphoric acid, inositol phosphoric acid, cytidylic acid, etc.

organic soil. A soil which contains a high percentage (> 15 or 20%) of organic matter.

organic solvent. A chemical compound (usually liquid) containing carbon to dissolve another substance (the solute).

organogenesis. Development of individual plant organs such as leaves, tillers, floral organs, or roots.

origin. In referring to accessions in the germplasm collection, the site where the accession was collected.

Oryza glaberrima. A cultivated rice species in West Africa.

Oryza nivara. An annual wild species of rice from South and Southeast Asia which is the only known source of resistance for the grassy stunt virus biotype one.

Oryza sativa L. The most important cultivated rice species, indigenous to Asia.

osmosis. The passage of water or another solvent through a semipermeable membrane from a region of low solute concentration to a region of high solute concentration.

outbreeding. A system of breeding that involves crossing unrelated parents.

outcrossing. A cross of different genotypes usually under natural conditions. This may also refer to cross-pollination.

outbreak. A sudden increase in pest population resulting in economic damage to the rice crop.

oval. Broadly elliptical.

ovary. The bulbous, basal portion of the pistil which contains one ovule.

ovate. Egg-shaped, widest toward the base.

overdominance. An effect in the heterozygote, A/a, which is greater than that in the homozygous dominant, A/A.

oviposit. In insects, to lay or deposit eggs.

oviposition. The way in which an insect deposits eggs.

oviposition cage. A cage where an insect lays eggs on plants or other materials.

ovoid. Ovate or oval solid.

ovule. A minute structure which, after fertilization, becomes a plant seed. The immature seeds before fertilization.

ovum. Female reproductive cell.

ozone depletion. Reduction of the ozone layer in the atmosphere. Influenced by aerosols and other gaseous pollutants.