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Glossary of Terms

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The ratio between genetic variance and phenotypic variance used by plant breeders in selecting for yield, resistance or other characteristics.

Habgood name
A number representing a combination of genes in the mathematical system of nomenclature devised by Habgood (1970).

A place with a particular kind of environment where plants and animals live.

Habitat, duration stability
The length of time the particular habitat type remains in a particular geographical location.

Habitat, temporal variability
The extent to which the carrying capacity (k) of a habitat varies during the time that site is tenable by the organism (i.e. temporal heterogeneity).

Habitat, spatial heterogeneity
Spatial continuity versus patchiness.

Agglutination of red blood corpuscles.

A condition in which the urine contains haemoglobin and is therefore stained red.

A medicine which increases the haemoglobin content of the red cells in the blood.

The presence of blood in the urine.

A reduction or oxidation written alone. Two half-reactions may be combined to form a complete electrochemical reaction.

Half saturation level
The level of some independent variable at which some process rate is reduced to half its maximum relative to that independent variable. It is applied to such processes as the effect of nutrient availability on phytoplankton nutrient uptake or the effect of prey density on predator feeding rate.

Having one parent in common.

Haller's organ
Depression on the first tarsi of ticks; functions as olfactory and humidity receptor.

Organism requiring salt for growth. An organism that grows best at high concentrations of salts.

Short-knobbed appendages of true flies; modified hind wings. Vestigial wing on the metathorax of a fly of the order Diptera; necessary for balance during flight.

Disease resulting from blockage of the nasopharynx by a parasite.

Large hooks on the opisthaptor of a monogenetic trematode, referred to as anchors by American authors.

Handling time
The act of quelling, killing and eating a prey, and then cleaning and resting by a predator are collectively known as the handling time.

Having one set of chromosomes in a cell or an individual. Haploidy is a characteristic of sex and germ cells.

Haploid parthenogenesis
The situation in which the unfertilised egg hatches and develops normally to produce a viable male adult whose cells contain only the haploid number of chromosomes.

A small, separable non-protein part of certain antigen molecules which carries the chemical group that combines with the antibody. The injection of a hapten into an animal does induce antibody formation.

A horizon of the soil that is hardened or cemented.

Hard water
Water which contains certain minerals, usually calcium and magnesium sulphate, chlorides or carbonates in solution to the extent that a curd or precipitate rather than a lather occurs when soap is added. Very hard water may cause objectionable precipitates in some herbicidal sprays.

(1) A loss to a species or individual consequent on damage. (2) A function of the concentration to which the organism is exposed and of the time of exposure.

Direct loss per plant or per part of plant.

Harmful organisms
Comprehensive term to include vertebrate or invertebrate pests, pathogen and weeds.

Harvest aid chemical
Material applied to a plant before harvest to facilitate harvesting by reducing plant foliage.

Harvest intervals
The period between the last application of a pesticide to a crop and the harvest, usually defined by law.

Hatching factor
A material produced by the roots of certain plants that is believed to increase the hatching of eggs of certain nematodes.

Above-ground parts of a plant (stem and leaves), especially of potatoes.

Haulm killer
Chemical for killing off potato plant tops to facilitate harvest.

Absorbing organ of certain parasites. A projection of fungal hyphae into host cells which acts as a penetration and absorbing organ.

The cured dry forage of the finer-stemmed crops e.g. grass.

The probability that a substance will cause harm under conditions of exposure.

Hazard identification
The identification of the chemical of concern, its adverse effects, target populations and conditions of exposure.

Hazard prediction/identification
The process of recognising a potential risk, involving both toxicity assessment and exposure assessment. Toxicity assessment determines the nature and extent of adverse health effects that the chemical in question can exert related to dose. Exposure assessment characterises exposed populations and where possible estimates exposure levels or doses incurred. The major objective of this process is the integration of toxicity dose responses and exposure data to provide dose-response relationships.

A dense cluster of sessile, or nearly sessile, flowers on a very short axis or receptacle, as in alsike clover and sunflower.

Head rice
The kernels of milled rice which are _ kernel size or larger.

Head yield
The amount of head rice obtained when paddy is milled. It is the total rice less the brokens.

Oestrous, season, or bulling. The time when a female is receptive to the bull. The phenomenon precedes ovulation when the ripe egg is shed from the ovary and passes into the uterus.

Low vegetation with shrubs.

Heat test
Iberia heat-tolerance test. A measure of adaptation to high temperatures as shown by the least rise in body temperature. The rectal temperature in animals is measured in degrees Fahrenheit at 10 am. and 3 pm. on each of three days when the air is still and in clear sunshine; the ambient temperature should be 85-90°F. These six rectal temperatures are averaged. Adaptability to heat = 100-10 (average rectal temperature - 101.0).

Heat therapy
High-temperature treatment for control of virus and other diseases.

Heel fly
Fly maggot of the family Hypodermatidae. Also called a warble.

A bovine female from birth (heifer calf) to calving herself. Sometimes used until she calves a second time but this is a confusion best avoided, e.g. second-calf heifer.

Turning toward the sun.

A member of the large group of primitive worms including nematodes and the worms parasitic in animal gut and tissues.

Agglutination of red blood cells.

The top pair of wings of true bugs, which have their basal ends thickened and their distal ends membranous.

The partly thickened forewing of the order Heteroptera.

A group of polysaccharides resembling cellulose and occurring in the cell wall.

Insects having a simple metamorphosis, like that in the Orthoptera, Heteroptera and Homoptera.

Hemimetabolous metamorphosis
Gradual metamorphosis in insects, in which the nymphs are generally similar in body form to the adults and become more like the adults with each instar.

An organism that is usually a parasite, but capable of leading a saprophytic life.

Main body cavity of arthropods, the embryonic development of which differs from that of a true coelom but which includes a vestige of a true coelom.

Bloody urine.

Fluid within the hemocoel of arthropods; also, the pseudocoelomic fluid of nematodes.

Lysis of red blood cells.

Pertaining to the liver.

Swollen liver and spleen.

Harmful to the liver.

A substance that causes damage to the liver.

Any vascular plant which is not woody.

Referring to plants with soft stems (not woody), such as annuals, biennials and perennials that normally die back to the ground in the winter.

Herbs, collectively, especially the aerial portion. Low growing plants used for fodder.

Any substance or mixture of substances intended for preventing, destroying or controlling any weed, including any algae or aquatic weed.

Herbicide chronicity
The concept where long-term exposure to low concentrations of a herbicide is as, or more phytotoxic than short exposure to a high concentration of herbicide.

Herbicide, hormone-type
Herbicide in which the active ingredient has growth-regulating properties.

Herbicide, residual
Herbicide showing persistent effect when applied to soil.

Herbicide, selective
Herbicide possessing differential toxicity to certain weeds and crop plants.

Herbicide, total
Herbicide affecting all plants.

Organism that feeds on plant material, contrast with carnivore.

That portion of the observed variance in a progeny that is inherited.

Possession of gonads of both sexes by a single (monoecious) individual.

Bisexual. In a flowering plant, having both stamens and carpels in the same flower; in an animal producing both male and female gametes.

Cloth made from hemp or jute.

A condition in which two or more genetically different nuclei occur in one cell.

Specialised cell in filamentous cyanobacteria frequently associated with nitrogen fixation.

A double-stranded DNA in which one strand is from one source and the other strand from another, usually related, source.

With an annual alternation between primary and secondary hosts (usually unrelated) (opposite of autoecious). Pertaining especially to rust fungi.

Fermentation of glucose or other sugar to a mixture of products.

Differing in kind; unlike qualities, different characteristics; dissimilar; mixed.

Heterogonic life cycle
Life cycle involving alterations of parasitic and free-living organisms.

A cell which contains at least two nuclei from different cell types.

The condition in which a mycelium contains two genetically different nuclei per cell.

Heterologous antigen
An antigen reacting with an antibody other than the one it induced.

Heterologous reaction
A serological reaction in which an anti-serum is reacted against an antigen other than the one used in its preparation.

Heterophile reaction
Antigen-antibody reaction, in which the antibody was not specifically elicited by the antigen to which it binds.

Increased growth, vigour or yield frequently shown in the F1 generation of a cross. Hybrid vigour.

The condition in which fungi produce compatible male and female gametes on physiologically distinct mycelia.

Hyperplastic symptom in which an organ develops in a position other than its normal one (e.g. the development of 'ears' in the tassels of corn plants).

Organisms which obtain energy and materials by eating other organisms; contrast with autotroph, a consumer as opposed to a producer.

Refers to organisms that are dependent upon outside sources for growth, being incapable of synthesising required organic materials from inorganic sources. Heterotrophs obtain their food from other organisms, living or dead.

Living within more than one host during a parasite's life.

Having a dominant and a recessive gene of a pair in the same cell or organism. An organism can be heterozygous for one or several genes.

Oncosphere; a six-hooked larva hatching from the egg of a eucestode.

Hexose monophosphate pathway (HMP)
Reaction sequence used primarily to synthesise pentosese from hexoses.

Period of dormancy in winter or cool season during which metabolism decreases; in mammals temperature drops close to that of surroundings.

A structural relationship in which each unit consists of two or more sub-units, the latter being similarly sub-divided.

Highly flammable liquid
A liquid having a flash point of less than 21°C as determined by a closed cup method.

See spray vii.

The scar on a seed which marks the point of its attachment to the pod or seed stalk.

Having long stiff hairs e.g. hirsute leaves.

The microscopic study of the chemical characteristics of tissues, through the use of substances (dyes etc.) producing identifying chemical reactions.

The study of the anatomy of tissues and their cellular structure.

Pertaining to histopathology, i.e. the study of the minute structure of diseased tissue, generally by staining and examination under the microscope.

A study of abnormal microscopic changes in the tissue structure of an organism.

Historical analogy
A method for forecasting the sales of a newly introduced product (or service) that uses the sales history of some previously introduced product as a guide.

Historic cost accounting
The recording of transactions at the actual cost incurred at the time of purchase irrespective of the item's current value.

Dwelling with the tissues of a host.

An adhesive material at a localised position on a cell, enabling the cell to attach to a surface.

Holding capacity
The amount of paddy in a continuous-flow dryer at one time; however it is not necessarily the drying capacity nor the throughput capacity of the dryer e.g. a continuous-flow dryer may have a 6 ton holding capacity, a 12 ton through put capacity and an average drying capacity of 2% pass (Wimberley, 1983).

Pertaining to a medium (used for growing organisms) whose intended constituents, other than purified inert materials, have exactly known chemical structure before the medium is compounded.

Hollow cone
Spray jet for pesticide application having a core of air breaking to give drops in an annular pattern.

Hollow fibres
A formulation for controlled release of chemicals based on a reservoir of active chemical held in the bore of the fibre and released by diffusion through the air layer above the chemical. Other systems relevant to pest control include foams and impregnated porous plastics e.g. polyvinyl chloride (PVC).

Holoblastic cleavage
Each nuclear division in an early embryo that is accompanied or closely followed by complete cytokinesis, the nuclei being separated by cell membranes.

Holocarpic reproduction
In fungi, reproduction in which the entire fungal body (thallus) is segmented into spores.

Having an annual sexual phase in which parthenogenesis is interrupted by the production of male and female sexual morphs (opposite of anholocyclic).

Insects which undergo a complete metamorphosis i.e. insects with a larva, pupa and adult.

The condition of being dead.

Holophytic nutrition
Formation of carbohydrates by chloroplasts.

Holozoic nutrition
Feeding by active ingestion of organisms or particles.

Maintenance of constancy or a high degree of uniformity in functions of an organism or interactions of individuals in a population or community under changing conditions, because of the capabilities of organisms to make adjustments.

Pertaining to 'warm-blooded' animals that regulate their body temperature; contrast with poikilothermic.

'Warm-blooded' animals, whose body temperature is maintained above that of usual surroundings.

Fermentation of glucose or other sugar leading to virtually a single product, lactic acid.

Uniform as to kind; showing no variability.

Homogonic life cycle
Life cycle in which all generations are parasitic or all are free living; there is no (or little) alteration of the two.

Homologous antigen
An antigen reacting with the antibody it had induced.

Homologous chromosomes
Chromosomes which pair at the first division in meiosis; each member of a pair has a corresponding sequence of gene loci and is derived from a different parent.

Homologous reaction
A serological reaction in which an anti-serum is reacted against the antigen used for its preparation.

Similarity in the sequence of monomers which make up different polymers; e.g. similarity in the base sequence of two different DNA or RNA molecules.

The condition in which sexual reproduction can only occur within the fungal mycelium; compare with heterothallic.

Homothetogenic fission
Miotic fission across the rows of cilia of a protozoan.

Of a cell or organism having both genes of a pair dominant or recessive an organism may be homozygous for one, several or all genes.

An individual the parent of which contributed to it a similar number of any given number pair of genes and whose germ cells are all alike in regard to the genes for that character.

Liquid with high sugar content discharged from the anus of some insects of the order Homoptera.

Dorsal wall of the camerostome that extends over the capitulum.

Hop blower
Rotary-blower duster for hops.

Horizon (soil)
A layer of soil, roughly parallel to the surface of the soil, with distinct characteristics which were produced by soil-forming processes.

Horizontal resistance
A resistance trait that does not involve a gene-for-gene relationship, i.e. any resistance that is not vertical resistance.

Horizontal transmission
Transmission between plants that are contemporaneous with each other.

A motile segment of a filamentous cyanobacteria, usually involved in dispersal.

A chemical agent that controls various physiological processes within an organism e.g. adrenaline stimulates the heart; auxins and cytokinins in plants stimulate cell proliferation and growth.

Hormone spray
See spray viii.

A caterpillar with dorsal spine or horn on the last abdominal segment - larvae of the family Sphingidae.

Organism that furnishes food, shelter or other benefits to another organism of a different species.

Host plant resistance
A method of pest control in which resistant, tolerant or unattractive host organisms are used. The inherited qualities of resistance influence the extent of pest damage.

Host range
The various kinds of host plants that may be attacked by a parasite.

Host specificity
The degree of restriction of the number of different plants or animals species that can serve as a food source for herbivorous or carnivorous species.

Hot fogging concentrate
A formulation suitable for application by hot fogging equipment.

Hull or husk
The lemma and palea attached to the caryopsis after threshing. To remove hulls from seeds.

Human resource accounting
Attempts by accountants to place a value on human assets in an enterprise.

Material added to a spray to delay evaporation of the water carrier.


Humid climate
A climate with sufficient precipitation to support forest vegetation: 50 cms or more in cool regions; up to 152 cms in hot regions.

The condition of the atmosphere in respect of its water vapour content. The word 'humidity' used alone generally signifies relative humidity, but various other measures are employed such as humidity mixing ratio, vapour concentration, vapour pressure, specific humidity, dew point etc.

Humoral immune response
Binding of antigen with soluble antibody in blood serum; also, the entire process by which the body responds to an antigen by producing antibody to that antigen.

Humoral immunity
An immune response involving the activities of antibodies.

The well-decomposed, more or less stable part of the organic matter of the soil.

Husking or dehusking
The process of removing the husk from the hulling or shelling grain during milling.

Transparent, colourless.

Hyalommine toxin
Toxin derived from a tick of the genus Hyalomma.

The first generation offspring of a sexual cross fertilisation between two individuals differing in one or more genes i.e. a heterozygote.

The fusion of a malignant cell with a single B-lymphocyte to produce a malignant lymphocyte producing monoclonal antibody.

Hybrid vigour
see Heterosis.

The process by which organisms of unlike hereditary constitution are crossed to produce F1 progeny with genes for the characteristics of both parents i.e. cross breeding.

An antibody-secreting cell line which is immortal. A hybrid cell resulting from the fusion of a tumour (cancer) cell and a normal cell such as a lymphocyte from the spleen. The fused cells can be cloned and, being derived from a simple spleen cell, will secrete a pure antibody.

Hydatid cyst
Metacestode of the cyclophyllidean cestode genus Echinococcus, with many protoscolices, some budding inside secondary brood cysts.

Hydatid sand
Free protoscolices forming sediment in a hydatid cyst.

Structures with one or more openings that discharge water from the interior of the leaf to its surface.

The addition of water.

Hydraulic sprayer
See sprayer iii. A machine which applies pesticides by using water at high pressure and volume to deliver the pesticide to the target. Same as high pressure sprayer.

Compounds consisting essentially of carbon and hydrogen. The important classes of hydrocarbons are paraffins, naphthaenes, olefins and aromatics. Ordinary commercial products derived from crude oil are normally made up of these four classes of compounds in varying proportions.

Chemical process of breakdown or decomposition involving a splitting of the molecule and addition of water molecule. e.g. during pesticide breakdown.

Causing hydrolosis or the reaction between a compound and the hydrogen and hydroxyl ions.

A condition in which the pericardial sac (the fibrous tissue sac in which the heart is contained) is filled with an excess of fluid.

Describes the molecule or group of atoms having, usually because of hydrogen bonding, a strong affinity for water i.e. water attracting.

Hydrophilic/lipophilic balance
The ratio of the water/oil affinities of an emulsifier.

Opposite of hydrophilic. Water repelling.

Plant that grows wholly or partly immersed in water; compare with xerophyte and mesophyte.

The growing of plants in aqueous chemical solutions.

Necrotic symptom of disease characterised by water-soaking of tissues.

A condition in which the thoracic cavity is filled with excess fluid.

Having a marked ability to accelerate the condensation of water vapour.

A fertile layer of regularly arranged asci or basidia in fungal fruiting bodies.

Excess of blood, usually to a tissue or organ.

Excessive sensitiveness of the skin, usually in the area of a diseased tissue.

Presence of amino acids in the blood or hemolymph in excess of the normal amount.

Hypergeometric probability distribution
Appropriate when sampling from a finite population of N elements of which k are identified as 'successes' and (N - k) are 'failures'. Then p(x) gives the probability of observing x successes in a sample of n selected from the population.

Having a very high antibody titre.

A type of complete metamorphosis in insects in which the different larval instars represent two or more different types of larvae.

A parasite whose host is another parasite.

A malformation caused by an increased number of functional units of an organ (organelles, cells, tissues), excluding tumour formation, whereby the bulk of the organ is increased in response to increased functional demands.

Detachment of a tapeworm proglottid while still juvenile, before eggs are formed.

Type of metamorphic development in which different larval instars have markedly dissimilar body forms.

Condition in which an organism is a parasite of another parasite.

Usually used to characterise a host whose initial reactions to infection are so strong as to limit further development of the invading parasite.

Hypersensitive reaction
A rapid response of a host to a parasite in which death of a portion or all of the host ensues.

Excessive sensitivity of plant tissues to certain pathogens. Affected cells are killed quickly, blocking the advance of obligate parasites. Also an immune reaction, usually harmful to the animal, caused either by antigen-antibody reactions or cellular-immune processes.

Abnormal increase in size (weight) and functional capacity of an organ or tissue, without an increase in the number of structural units upon which their functions depend; hypertrophy is usually stimulated by increased functional demands.

Hypha (pl. hyphae)
One of the simplest branched filaments of the mycelium of a fungus that is composed of one or more cylindrical cells and that increases in length by growth at its tip. New hyphae arise as lateral branches.

A short mycelial branch.

A lowering of the cholesterol content of the blood.

The stem of the embryo or young seedling below the cotyledons.

The cellular layer beneath the cuticle of a nematode.

The lower region of a stratified lake, not subject to wind mixing during at least part of the year. Below the thermocline.

More rapid growth of the lower side of an organ (e.g. a petiole) than of the upper side.

Tongue-like lobe arising from floor of mouth in insects; variously modified for feeding in many groups.

A malformation caused by the underdevelopment of cells, tissues or organs. A hypoplastic organ or tissue is one that never reaches normal size; sometimes used to indicate an atrophy caused by the destruction of some of the elements (e.g. cells) rather than a general reduction in size.

Hypostatic gene
A gene whose properties are suppressed in the presence of another (epistatic) gene.

Portion of the mouthparts of acarines; composed of fused coxae of pedipalps.

Inner half wall of a diatom cell.

Underdevelopment of a tissue or plant due to abnormally reduced cell enlargement.

The phenomenon by which a strain of a pathogen is less virulent than normal. In some fungi infection with dsRNA is thought to be responsible.

Combination of the metapodosoma and opisthosoma of the body of a tick or mite.

An organism that for any given character possesses different genes inherited from the male and female parents. Heterozygous plants do not breed true.

A polygonal diagram resulting from plotting temperature means against rainfall.