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

T Terms

T. Aman. This rice is used in Bangladesh and eastern India for transplanted lowland rice, grown in the wet season when water depth does not exceed 0.5 m, approximately from July to September.

t-test. A statistical test criterion in comparing two samples of data believed to be normally distributed.

tag. A small marker usually tied to a plant, bag, or packet and used for identification and classification of samples.

talc. A silicate mineral that is extremely soft and has a soapy or greasy feel; used as talc powder.

target crop. One that has the potential to be a major crop, increasing the farmer's production and income.

tegmen. A covering or integument, such as the tough, leathery forewing of certain insects or the inner coat of a seed.

tegmen layer. Two layers of cells next to the pericarp of a seed which represent the inner cell layers of the inner integuments of the ovule. The tegmen is often mis-termed as testa which is derived from the outer integuments in the ovule and which is destroyed before the caryopsis ripens.

telomere. Terminal region of chromosomes characterized by repeated DNA sequences.

telotrisomic. A trisomic in which the extra chromosome has only one arm.

tempering. This means drying the grain on a drying pad for a number of hours or in a grain dryer, then tempering the grain by allowing it to cool for a number of hours in a bin or bag. This process should be repeated at least twice until the moisture is consistently at 14%.

tendril. A slender, clasping or climbing organ of a stem or leaf.

tensiometer. An instrument for measuring the amount of energy needed to extract water from the soil (usually expressed in kPa or cbars).

terrace. 1). Bench-like portions of a former flat river floodplain left at higher levels by the downcutting action of a river; alluvial terraces and river terraces are generally considered as synonymous.2). An artificially leveled field or series of fields made on sloping land.

terete. 1). Cylindrical or tapering, circular in cross-section. 2). Circular in cross-section.

terminal. At the end of branch or a stem.

tertiary tillers. Arise from secondary tillers and are the third group of tillers to grow during the plant's development.

test entries. Varieties or breeding lines being evaluated.

test insect. The insect species and biotype against which a test entry is being evaluated.

testa. Hard external coating or integument of a seed.

testcross. A cross made between cytoplasmic male sterile line and a test variety to identify maintainers and restorers.

testcross nursery. Breeding nursery where Fl progenies of cytoplasmic male sterile lines and test varieties are screened for pollen sterility/fertility and spikelet fertility to identify maintainers and restorers.

tester. A cross between a selection, line, or clone and a common pollen parent which may be a variety, inbred line, or a single cross. The common pollen parent is called the top cross or tester parent.

tester strain. A common parent, generally male, used in crosses with a series of lines in order to analyze the combining ability of lines.

tetraploid. An organism with four basic (n) sets of chromosomes.

thallus. A plantlike organism not divided into leaves, stem, and root. Mushrooms and lichen are examples of thalli.

thermocycler. An apparatus which changes temperatures according to precise programming. Usually used with PCR, RAPD, AP-PCR, and DAF.

thermosensitive genic male sterile line (TGMS). The genic male sterile plant which responds to temperature for expression of its pollen sterility/fertility.

Thermus aquaticus. Thermophylic bacterium found in hot springs. Its DNA polymerase enzyme is thermostable and is used in PCR, RAPD, and DAF.

thinning. Removal of some plants to attain the desired population density.

three-line breeding. Breeding methodology where three lines--cytoplasmic male sterile, maintainer, and restorer--are used to produce Fl hybrids.

three-way cross. When an F1 hybrid is crossed to a third variety or breeding line.

threshability. Ease by which the grains are removed from the panicle.

threshing. Operation of detaching or separating the rice grains from the panicle by hand or mechanical means.

threshold. 1). A phenomenon that can obscure the gene-character relationship. 2). A safe level of economic viability.

threshold moisture content. (biology) The minimum moisture condition, expressed either in terms of moisture content or moisture stress, at which biological activity just becomes measurable.

tibia. The fourth division of the insect's leg between the femur (thigh) and the tarsus or the foot.

tidal flats. Areas of nearly flat, barren mud periodically covered by tidal waters. Normally these places have an excess of soluble salt.

tidal wetlands. Areas where water levels in the ricefields fluctuate under the influence of tides.

till. To plow and prepare for seeding; to seed or cultivate the soil.

tiller. A vegetative branch of the rice plant composed of roots, culm, and leaves which may or may not develop a panicle. Shoot arising from the main culm (stem).

tillage. 1). The mechanical alteration of some physical properties of the soil to provide a condition appropriate for crop growth. 2). To cultivate the land, to gain moisture in the soil.

tiller blades. The soil-engaging part of a rotary tiller or tillage tool that cuts and turns the soil over.

tiller number. Number of tillers present in a rice plant.

tillering ability/capacity. The genetic potential of a given variety to produce a certain number of tillers.

tillering stage. Growth stage of the rice plant that extends from the appearance of the first tiller until the maximum tiller number is reached.

tilth. The physical condition of the soil as related to its ease of tillage, fitness as a seedbed, and its impedance to seeding emergence and root penetration.

tipburn yellow. A condition in which the yellowish seedlings die after the second foliage leaf is formed. The leaf apexes wither and die.

tissue culture. A technique of growing large pieces of tissue (explant) from different parts of a plant in semisolid or liquid medium under aseptic conditions. After the culture, masses of undifferentiated tissue are produced or plants are regenerated.

tolerance. Ability of a plant to withstand stress without yield reduction or injury.

topcross. A cross between a selection, line, or clone, and a common pollen parent which may be a variety, inbred line, or a single cross. The common pollen parent is called the topcross or tester parent.

toposequence. A sequence of soils in the landscape, from the crest to the valley bottom.

topdressing. The application of fertilizer materials after seeding or transplanting or after the crop has been established.

topsoil (surface soil). The uppermost part of the soil ordinarily moved in tillage, or its equivalent in uncultivated soils. Topsoil ranges from 8-10 cm to 20-25 cm in depth. It is frequently designated as the plow layer.

total factor productivity. The productivity of all inputs taken together.

total milled rice. Quantity of whole plus broken grains of milled rice that can be obtained from a given quantity of clean rough rice.

totipotency. Potential of cells or tissues to form all cell types and/or to regenerate a plant.

toxic. Of, relating to, or caused by a poison or toxin, poisonous, causes illness, reduces plant growth.

toxicity. The quality of being poisonous.

toxin. Any of the various poisonous substances produced by certain plants and animal cells including bacterial toxins, phytotoxins, and zootoxins.

traditional cultivars. Tall, weak-stemmed, long-duration, low-yielding cultivars grown by farmers for many years.

traffic pan (handpan). A 5- to 10-cm thick compacted subsurface horizon between the
10- to 40-cm depths; common in paddies.

trait. A distinguishing quality or character of a plant.

transcription. 1). Copying of a gene into RNA. Also, copying of a viral RNA into a cRNA. 2). The process by which DNA is copied into RNA. As the nucleic acid "language" stays the same (see genetic code), the process is called transcription.

transduction. Transfer of genetic material from one bacteria to another by means of a bacteriophage.

transfer RNA (tRNA). The RNA that becomes attached to an amino acid and guides it to the correct position on the ribosome for protein synthesis; there is at least one tRNA molecule for each amino acid.

transformant. A bacterial cell that has undergone transformation.

transformation. The genetic modification induced by the incorporation of "foreign" DNA into a cell.

transgenic. Descriptive of an organism that contains some genetic material that has been experimentally transferred into it from some other source.

transgressive segregation. A segregation pattern in which the segregants exceed the limits of the parents.

transient expression. Expression of a transforming gene by recipient cells over a relatively brief time span; does not necessarily indicate integration of the gene into the plant chromosome.

transitory yellowing. A virus disease of rice transmitted by green leafhoppers (Nephotettix nigropictus, N. cincticeps, and N. virescens). The characteristic symptoms are yellowing of leaves, reduced tillering, and stunting. The disease is similar to tungro since it is transmitted by the same insect.

translation (genetic). The process by which the genetic information of RNA is used to specify and direct the synthesis of proteins. Occurs in ribosomes.

translocation. 1). Genetic. Change in position of a segment of a chromosome to another location in the same or a different chromosome. 2). Physiological. The movement of assimilates (carbohydrates or nutrients) from one plant organ to another in response to stress or ontogeny. 3). Breakage and reunion of chromatid at a different point of the chromosome.

translucency. The opposite of chalkiness; measured with a Riken-Sanno Rice Meter which measures transmitted light through a fixed volume of rice grains, one model for brown rice, another for milled rice.

translucent. Transmitting light but causing sufficient diffusion to eliminate perception of distinct images; intermediate between clear and opaque.

transmitted nutrients. Nutrients moved to growing points during seed germination.

transovarial passage. Transmission of virus in the insect from one generation to the next through the egg.

transpiration. The process by which plants release water vapor to the atmosphere through surface pores (stomatal openings) in the plant foliage in response to atmospheric demand. The water of transpiration usually reaches a maximum value in the afternoon and a minimum value just before sunrise. Soil moisture content and plant characters, such as location and distribution of stomata, reduction of transpiration surface (leaf rolling), and plant age, affect transpiration rate.

transplant. To remove seedlings from the nursery (seedbed) and plant them in the field either by hand or machine.

transposon. Transposable element in either prokaryote or eukaryote. May contain its own transposase enzyme gene. Usually is flanked by direct or indirect repeat sequences.

transverse. Across the long axis.

trap crop. A crop that is planted specifically to attract pests, rodents, or birds away from the main crop.

treatment. A general term denoting different effects which are to be compared or the effects or factors that are to be measured. (e.g., variety, fertilizer rates) or procedures (e.g., method of nitrogen application).

trial. An experiment to determine or test the quality or performance of a specific variety, system, or crop rotation and its usefulness in increasing farmers' production.

triangular hull (tri). The spikelet appears triangular because the lemma is so shaped.

trifoliate. Having three leaflets.

trigonous. Three-angled

trihybrid. A hybrid rice from a cross between parents differing in three specific genes.

trim. See Clip leaves.

triple crossing. Sequential crossing of three cultivars, (e.g., for A, B and C, A x B, AB x C, ABC x A, ABCA x B, and so on.

triplex. A polyploid recessive at all loci except three with respect to a particular gene.

triploid. An organism with three basic (n) sets of chromosomes.

trisomic. An organism diploid except for one kind of chromosome which is present in triplicate, hence, having 2n + 1 chromosomes.

truncate. Cut-off somewhat squarely at the end.

tuber. A short thickened underground stem.

tubercle. Any small, rounded projection.

tuberous. Bearing a tuber.

tufted. Having many short, crowded branches all arising from about the same point.

tungro. A viral disease transmitted by green (Nephotettix spp.) and zigzag leafhoppers (Recilia dorsalis). The diseased plants are characterized by stunting and reduced tillering. The leaf color ranges from light yellow to orange-yellow. Yellowing usually starts from the tips of the leaves. The panicles are often not fully exserted. The grains are usually covered with dark brown blotches.

tunneling. Making a passage through plant material by the feeding of larvae.

turnaround time. The time interval between harvesting of the existing crop and planting of the next crop in a cropping sequence.

turnrow (turn strip, head land). The land at the margin of a field on which the plow or other equipment may be turned.

two-line breeding. Hybrid rice breeding methodology where only two lines, a male sterile (either photosensitive, thermosensitive, or chemically induced) and a pollen parent are used for the production of Fl hybrids.