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A genetically and often geographically distinct mating group within a species; or a group of pathogens that infect a given set of plant varieties.

Race non-specific resistance

Resistance to all races of a pathogen. Synonymous with horizontal resistance. This form of resistance is commonly, but not necessarily, polygenic.

Race specific resistance

Resistance to some races of the pathogen but not to others. Synonymous with vertical resistance.


A more or less conical inflorescence within flowers arising alternately from a common axis, the youngest towards the tip.


The small axis below the lemma and palea, bearing the single floret.


1) The axis of a spike or raceme, or of a compound leaf. 2) The elongated axis of a panicle.


A unit of measure of absorbed doses of ionizing radiation, which represents absorption equal to 100 ergs of energy per gram of irradiated material. (A RAD is an acronym for radiation absorbed dose and is a unit of absorbed dose.)


Spreading from the center.


The embryonic primary root unsheathed by the coleorhiza and the root cap, persisting only for a short time after germination.


A radiometer is a device for measuring the radiant flux (power) of electromagnetic radiation. Generally, it denotes an infrared radiation detector, yet it also includes detectors operating on any electromagnetic wavelength.

Ragged stunt

A viral disease of rice transmitted by the brown planthopper Nilaparvata lugens. The diseased plants are characterized by the presence of ragged and twisted leaves, vein swellings, and nodal branches. There is delay in flowering and incomplete emergence of panicles; the panicles bear mostly unfilled grains.

Rained Lowland Rice Eco System

Rainfed low-land rice is grown in such areas as East India, Bangladesh, Indonesia, Philippines, and Thailand, and is 25 % of total rice area used Worldwide. In India, low land rice area is about 14.4 million hectares, which accounts 32.4 % of the total area under rice crop in the country. Production is variable because of the lack of technology used in rice production. Rainfed lowland farmers are typically challenged by poor soil quality, drought/flood conditions, and erratic yields.

Rainfed rice

Rice grown on leveled bunded fields to allow an accumulation of flood water on the surface during heavy rains. Grown in areas that depend entirely on rain for moisture for its water supply.

Rainfed Upland Rice Eco System

Upland zones are found in Asia, Africa, and Latin America. In India, the total area under upland rainfed rice in the country is about 6.00 million hectares, which accounts 13.5 % of the total area under rice crop in the country. Upland rice areas lies in Eastern Zone comprising of Assam, Bihar, Eastern Madhya Pradesh, Orissa, Eastern Uttar Pradesh, West Bengal and North-Eastern Hill region. Upland rice fields are generally dry, unbunded, and directly seeded. Land utilized in upland rice production can be low lying, drought-prone, rolling, or steep sloping.


Arrived at by chance without the exercise of any choice.

Random Amplified Polymorphic DNA (RAPD)

DNA amplification method which uses single primers. Method is restricted to primers 9 nucleotides and larger, and amplification products are generally visualized using agarose electrophoresis and ethidium bromide fluorescence.

Random sample

A sample selected according to some chance mechanism such that every unit in the population has a known probability of being in the sample. These samples are obtained by using a random mechanism such as drawing of lots or using a table of random numbers.


A process of allocating treatments to the experimental units so that each experimental unit has an equal chance of receiving any of the treatments. It is a necessary condition for obtaining a valid estimate of the experimental error. Location of treatments by chance so as to provide unbiased estimates of treatment means and experimental error.

Randomized block design

An experimental design in which the experimental area is divided into blocks and all of the treatments are randomly arranged within each block.


The variation of data from highest to the lowest value.


1) The ridge connecting the two ends of an anatropous ovule. 2) A seamlike joining of the two lateral halves of an organ, as in the ridge of tissue along the side of an ovule, which indicates the position of the vascular bundles supplying the developing seed.

Rapid Generation Advance (RGA)

A part of a breeding procedure wherein the segregating populations are grown at very close spacing, high temperature, and short days to shorten growth duration, thus making possible several generations per year. The duration from F2 to F5 which generally takes about 4 years can be shortened to 2 years.


Classifying test entries based on degree of plant damage, number of insects, etc., by expressing on a numerical scale, usually 0-9. It is relative estimate.


New tillers that grow from the stubble of harvested plants and may bear grains. These new tillers constitute the ratoon crop.

Ratoon cultivation

Cultivation of growth from stubble after a crop has been harvested to develop another crop. Conducted in level bunded fields where water is readily available for irrigation.

Raw rice

Dehulled and milled rice not subjected to steaming or parboiling.

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