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Objective

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

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.   

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.

Off-season crop

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

Off-season tillage

It refers to tillage operations done not for immediately raising crop plants but conditioning the soil suitably for the forthcoming main season crop like Post harvest tillage, Summer tillage, Winter tillage and Fallow tillage. These are scheduled during un cropped seasons for levelling to the desirable grade, leaching to remove salts, lowering of a seasonal water table & reducing the population of harmful flora and fauna in the soil.  

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.

Opaque

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

Open hull

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

Open pan evaporimeter

Used to measure the evaporation of water. The pan evaporimeter consists of a cylindrical reservoir made from copper sheet of fixed diameter and depth, filled with water to a few centimetres below the rim. A fixed-point gauge in a stilling well serves to indicate the level of water in the pan. A calibrated measuring cylinder is used to add or remove water at each observation to bring the water level to the fixed point. The cross-sectional area of the measuring cylinder is such that, the number of millimetres of water added from the measuring cylinder divided by 100 gives the amount of water in millimetres which has evaporated from the pan during a given interval of time. The reservoir is covered with wire-mesh netting to protect the pan from birds and animals. A thermometer suspended from a mounted clamp to the side of the reservoir, records the temperature of the water in the pan.

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 / Normal 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 Mycoplasma like 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.

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