A Food Freshness Technology Holdings company

Glossary of Terms

General Glossary


The uptake of liquid or gas into the fibres of a substance, material or membrane.

Climacteric fruit

Climacteric fruit continues to ripen after being harvested eg Apples, Pears, Nectarines, Peaches, Plums.

Controlled Atmosphere (CA)

A controlled atmosphere is an agricultural storage method in which the concentrations of oxygen, carbon dioxide and nitrogen, as well as the temperature and humidity of a storage room are regulated. Both dry commodities and fresh fruit and vegetables can be stored in controlled atmospheres.

e+ô active

This is the name of the active ingredient in the Itís Fresh! filters. It is made from a proprietary blend of clay and minerals.

The combination of the porous nature of the clay and the formulation of the minerals means e+ô only adsorbs certain molecules. It is therefore highly selective and significantly attracts ethylene. It therefore has no effect on larger desirable molecules such as flavour and aroma compounds, which leaves them present in and around the fruit for consumers to enjoy.


Ethylene gas (C2H2) is an odorless, colorless gas that exists in nature and is also created by man-made sources. As fruits, vegetables and floral products mature, ethylene gas is released into their packaged environment. Ethylene is responsible for the changes in texture, softening, colour, and other processes involved in ripening.

In many cases, perishable products (such as fruits, vegetables and flowers) are sensitive to ethylene gas and can ripen or mature quicker when exposed to ethylene gas. In addition, certain fruits and vegetables are high producers of ethylene gas thereby creating the need to separate, ship, or store produce based on their ethylene profile.

Ethylene management

Itís Fresh ethylene filters and films allow growers and retailers of ethylene producing and ethylene sensitive goods to transport and store product without the fear of premature ripening. By removing ethylene from the storage, transportation and retail environment, quality can be maintained and spoilage reduced.

Ethylene removal filter

Ethylene removal filters and sheets and can extend the shelf life of fruits, vegetables and flowers in a packaged or bulk environment. These products remove unwanted ethylene gas through the, thereby ensuring the quality of freshness of the product while in transit or in storage.

Farm to fork

A commonly used phrase that indicates the lifecycle journey of produce from its point of harvest (on the farm) to end-user consumption (on the pate).

Food security

Food security is a condition related to the supply of food, and individuals' access to it. The report of the 1996 World Food Summit states that food security "exists when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life".

Food insecurity, is a situation of "limited or uncertain availability of nutritionally adequate and safe foods or limited or uncertain ability to acquire acceptable foods in socially acceptable ways", according to the United States Department of Agriculture (USDA).

Food waste

Food waste or food loss is food that is discarded or lost uneaten. The causes of food waste or loss are numerous, and occur at the stages of production, processing, retailing and consumption.

Current estimates put global food loss and waste between one-third and one-half of all food produced. Loss and wastage occurs at all stages of the food supply chain or value chain. In low-income countries, most loss occurs during production, while in developed countries much food is wasted at the consumption stage.


The creation of a protective atmosphere around produce that removes harmful and unwanted materials and provides extended quality, freshness and flavour.

Fruit respiration

Respiration is the process by which plants take in oxygen and give out carbon dioxide. As oxygen from the air breaks down carbohydrates in the plant into carbon dioxide and water. This reaction produces energy in the form of heat.

Respiration is a basic reaction of all plant material, both in the field and after harvest. It is a continuing process in the growing plant as long as the leaves continue to make carbohydrates, and cannot be stopped without damage to the growing plant or harvested produce.

Fresh produce cannot replace carbohydrates or water after harvest. Respiration uses stored starch or sugar and will stop when reserves of these are exhausted; ageing follows and the produce dies and decays.

Fruit ripeness

What exactly does it mean for fruit to be ripe? The ripening process of fruit is the conversion of starch to sugar. When fruit is early in the ripening process, it is very starchy, which causes it to be hard and odourless. As fruit ripens, more sugar develops, which causes it to soften, change colour, and put off a sweet aroma.

The ripeness of a fruit can be judged based on; colour, texture, aroma and weight. The ripeness of fruit allows farmers and processors to minimize losses and maximize quality through accurate categorization of produce quality.

Gas exchange

The transfer of gases between an organism and its environment, e.g. the process by which oxygen enters the fruit or pack and carbon dioxide is expelled from it.

Itís Fresh! berry pad

Itís Fresh! pads are provided to growers and pickers as a filter integrated into a berry pad, pre-inserted into punnets and clam shells.

Itís Fresh! Filter

Our filters are packed conveniently in easily handled cartons. They are ready for hand insertion into retail or food service packs anywhere along the supply chain, from picking to packing and from lidding to ripening.

Itís Fresh! Label

The Itís Fresh! label provides an automated, integrated packaging solution with the unique Itís Fresh! active material printed onto a normal pack label and can be flexibly used for any kind of pack utilising a normal labelling line. The label was developed for use on top sealing or flow-wrapping packing lines.

Itís Fresh! transit sheet

Produced in, small and large sizes for use in transit cases RPCs and other larger rigid or flexible packages of loose fruit.

Modified Atmosphere Packaging (MAP)

MAP or modified atmosphere packaging is the process of packaging fresh food by regulating the oxygen and carbon dioxide content inside the package to improve the foodís shelf life.

Non-Climacteric fruit

Non-climacteric fruit ceases to ripen after it has been harvested eg Oranges, Grapes, Pomegranate

Plant hormone

Ethylene is thought of as the Ďaging hormoneí in plants. In addition to causing fruit to ripen, it can cause plants to die. It can be produced when plants are injured, either mechanically or by disease.

Post-harvest technology

In agriculture, postharvest handling is the stage of crop production immediately following harvest, including cooling, cleaning, sorting and packing. The instant a crop is removed from the ground, or separated from its parent plant, it begins to deteriorate. Postharvest technology treatment largely determines final quality, whether a crop is sold for fresh consumption, or used as an ingredient in a processed food product.


Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In some countries, an advisory Ďbest beforeí, mandatory Ďuse byí, or freshness date is required on packaged perishable foods.

Supply chain

A supply chain is a network between a company and its suppliers to produce and distribute a specific product, and the supply chain represents the steps it takes to get the product or service to the customer. Supply chain management is a crucial process, because an optimized supply chain results in lower costs and a faster production cycle.


Sustainability is based on a simple principle: Everything that we need for our survival and well-being depends, either directly or indirectly, on our natural environment. To pursue sustainability is to create and maintain the conditions under which humans and nature can exist in productive harmony to support present and future generations.

Sustainable packaging

Sustainable packaging is the development and use of packaging which results in improved sustainability. This involves increased use of life cycle inventory (LCI) and life cycle assessment (LCA) to help guide the use of packaging which reduces the environmental impact and ecological footprint.

Companies have long been reusing and recycling packaging when economically viable. Using minimal packaging has also been a common goal to help reduce costs. Recent years have accelerated these efforts based on social movements, consumer pressure, and regulation. All phases of packaging, distribution, and logistics are included.

Technical Glossary


directed away from the stem of a plant; pertaining to the lower surface of a leaf (see adaxial)


pertaining to the absence of life, as diseases not caused by living organisms


to separate from a plant, as leaves, flowers, and fruits do when they fall


the shedding of leaves or other plant parts as the result of physical weakness in a specialized layer of cells (the abscission layer) that develops at the base of the structure

Acceptable daily intake (adi)

a measure of the level of a chemical, i.e. a pesticide residue, that is believed to be able to be consumed on a daily basis over a lifetime without harm; used by the u.s. government to establish safe levels of potentially hazardous substances in food

Acervulus (pl. Acervuli)

erumpent, cushionlike fruiting body bearing conidiophores, conidia, and sometimes setae


having a ph of less than 7

Acid precipitation

precipitation (fog, rain, snow) with a low ph, due to the presence of nitric and sulfuric acid formed by the reaction of air pollutants (n0x and s02) with water

Acid rain

precipitation with a low ph, due to the presence of nitric and sulfuric acid formed by the combination of air pollutants (n0x and s02) with water


upward from the base to the apex of a shoot of a plant; in fungi, the production of spores in succession in the direction of the apex so that the apical spore is the youngest (see basipetal)


a group of microorganisms similar to bacteria that produce long filaments


pertaining to symptoms that develop suddenly(see chronic)

Acute toxicity

ability of a single dose of a compound to poison (see chronic toxicity)


directed toward the stem of a plant; pertaining to the upper surface of a leaf (see abaxial)

Adpressed (syn. Appressed)

closely flattened down or pressed against a surface


arising from other than the usual place, as roots from a stem rather than as branches of a root


dikaryotic spore of a rust fungus produced in an aecium; in heteroecious rusts, a spore stage that infects the alternate host

Aecium (pl. Aecia; adj. Aecial)

the fruiting body of a rust fungus in which the first dikaryotic spores (aeciospores) are produced


occurring in the air


the act of infusing or forcing air into, for example, soil


living only in the presence of oxygen


chemical byproduct from aspergillus flavus and a. Parasiticus harmful to humans and other animals


jellylike material derived from algae and used to solidify liquid culture media; term also applied to the medium itself


relative ability of a plant pathogen to colonize and cause damage to plants (see virulence)

Air pollution

any air contaminant that causes undesirable effects on living organisms or materials


winged (see apterous)

Albino (n. Albinism)

white or light-colored; having a marked deficiency in pigmentation


having basic (nonacidic) properties; ph greater than 7


nitrogen-containing ring compounds produced by plants that cause physiological effects in animals


any of one or more alternative forms of a gene

Allelopathy (adj. Allelopathic)

ability of one species to inhibit or prevent the growth of another species through the production of toxic substance(s)

Alternate host

one of two kinds of plant on which a parasitic fungus (e.g. rust) must develop to complete its life cycle

Alternative host

a plant other than the main host that a parasite can colonize; alternative hosts are not required for completion of the developmental cycle of the parasite

Alternation of generations

a reproductive cycle in which a haploid phase alternates with a diploid phase

Amino acid

organic nitrogenous acids from which protein molecules are constructed


a chemosensory organ located in the anterior region of a nematode


having an antheridium through which the oogonium grows, as in many phytophthora species (see paragynous)


copulation of two unrelated cells and nuclei, e.g., egg and sperm; reproduction by a sexual process


able to move both upward and downward in phloem, as do some pesticides


living in the absence of oxygen

Anamorph (adj. Anamorphic; syn. Imperfect state)

the asexual form in the life cycle of a fungus, when asexual spores (such as conidia) or no spores are produced (see holomorph and teleomorph)

Anastomosis (pl. Anastomoses)

fusion between branches of the same or different structures (e.g. hyphae) to make a network


a plant that completes its life cycle and dies within one year (see biennial, perennial)

Annual ring

single-year growth of xylem in a woody stem


grooved bands in the cuticle of some nematodes


a general term for interference between organisms that may include antibiosis or competition for nutrients or space; action of two or more pesticides that reduces the effectiveness of one or all (see synergism)


an organism or substance that limits or counteracts the action of another


toward the front or head (see posterior)


pollen-bearing portion of a flower

Antheridium (pl. Antheridia)

male sexual organ (male gametangium) found in some fungi


the period of the opening of a flower during which pollination can occur


disease caused by acervuli-forming fungi (order melanconiales) and characterized by sunken lesions and necrosis


an association between organisms, or between an organism and a metabolic product of another organism, that is harmful to one of them


a chemical compound produced by one microorganism that inhibits growth or kills other living organisms


a specific protein formed in the blood of warm-blooded animals in response to the presence of an antigen


any foreign chemical (normally a protein) that induces antibody formation in warm-blooded animals

Antiserum (pl. Antisera)

blood serum containing antibodies

Apex (pl. Apices; adj. Apical)

tip of a root or shoot, containing the apical meristem


small, sucking insect of the family aphididae (order homoptera) that produces honeydew and injures plants when in large populations

Apothecium (pl. Apothecia)

open, cuplike or saucerlike, ascus-bearing fungal fruiting body (ascocarp), often supported on a stalk

Appressed (syn. Adpressed)

closely flattened down or pressed against a surface

Appressorium (pl. Appressoria)

swollen, flattened portion of a fungal filament that adheres to the surface of a higher plant, providing anchorage for invasion by a fungus


wingless (see alate)


able to be cultivated for agriculture

Arbuscular mycorrhiza (abbr. Am; syn. Endomycorrhiza)

symbiotic association between a nonpathogenic or weakly pathogenic fungus and the roots of plants in which fungal hyphae invade cortical cells of the root and produce vesicles and arbuscles (see ectomycorrhiza)

Arbuscule (adj. Arbuscular)

branched haustorial structure of certain endomycorrhizal fungi that forms within living cells of the root


member of the phylum arthropoda, which consists of animals with articulated bodies and limbs and which includes insects, arachnids, and crustaceans

Ascocarp (syn. Ascoma)

sexual fruiting body of an ascomycetous fungus that produces asci and ascospores; e.g. apothecium, ascostroma, cleistothecium, perithecium, pseudothecium


pertaining to ascus-producing hyphae

Ascogonium (pl. Ascogonia)

a specialized cell that gives rise to the hyphae that produce asci

Ascoma (pl. Ascomata; syn. Ascocarp)

sexual fruiting body of an ascomycetous fungus that produces asci and ascospores; e.g. apothecium, ascostroma, cleistothecium, perithecium, pseudothecium

Ascomycetes (adj. Ascomycetous)

a group of fungi, also called the ascomycota, that produces sexual spores (ascospores) within a saclike structure called an ascus


sexual spore borne in an ascus

Ascostroma (pl. Ascostromata)

a fruiting body containing bitunicate (double-walled) asci in locules (cavities); usually dark with multiple locules, but sometimes single (see pseudothecium)

Ascus (pl. Asci)

saclike structure containing ascospores (typically eight) and usually borne in a fungal fruiting body


having no cross walls; lacking septa; nonseptate; coenocytic


vegetative; without sex organs, gametes, or sexual spores; the imperfect or anamorphic stage of a fungus

Asexual reproduction

any type of reproduction not involving the union of gametes and meiosis

Audpc (abbr. For area under disease progress curve)

a measure of the total amount of disease over a period of time, determined from graphs of disease vs. Time, which can be used to compare epidemics quantitatively


in reference to rust fungi, producing all spore forms on one species of host plant (see heteroecious)


an organism that synthesizes its nutritive substances from inorganic molecules; e.g. plants capable of photosynthesis (see heterotroph)


plant hormone (growth regulator) influencing growth through cell elongation

Avirulence (avr) gene

gene in a pathogen that usually causes a hypersensitive reaction, is associated with active plant defense reactions in a resistant plant, and causes disease in a susceptible plant

Avirulent (syn. Nonpathogenic)

unable to cause disease (see virulent)


principle of plant disease control in which plants are grown at times or locations where the pathogen is inactive or not present


bristlelike structure at the apex of the outer bract of some cereal and grass flowers


culture in the absence of living bacteria or other organisms; pure culture


the angle formed by the leaf petiole and the stem


pertaining to or placed within an axil

Axillary bud (syn. Lateral bud)

bud that develops in the axil of a leaf


shaped like short rods with rounded ends


to cross (mate) an offspring with one of its parents

Bacterial streaming

large populations of bacteria that exude from the cut surface of infected plant tissue when observed with a microscope


a chemical or physical agent that kills bacteria


a protein antibiotic, one or more types of which can be produced and excreted by certain strains of bacteria


a virus that infects a bacterium

Bacterium (pl. Bacteria)

a prokaryotic, microscopic, single-celled organism with a cell wall that increases by binary fission


all tissues outside the vascular cambium of a woody plant, generally including the cork layers, cork cambium (phellogen), and phloem

Basal knob (syn. Stylet knob)

structure at the base of a nematode stylet


having a ph of greater than 7

Basidiocarp (syn. Basidioma)

sexual fruiting body of a basidiomycetous fungus

Basidioma (pl. Basidiomata; syn. Basidiocarp)

sexual fruiting body of a basidiomycetous fungus

Basidiomycetes (adj. Basidiomycetous)

a fungus group, also called the basidiomycota, characterized by the formation of external basidiospores on basidia


haploid (1n) sexual spore produced on a basidium

Basidium (pl. Basidia; adj. Basidial)

specialized cell or organ, often club-shaped, in which karyogamy and meiosis occur, followed by production of externally-borne basidiospores (generally four) that are haploid. There are several types of basidia.


downward from the apex toward the base of a shoot; referring to development in the direction of the base so that the apical part is oldest (see acropetal)


any insect of the order coleoptera characterized by elytra (thickened outer wings), chewing mouth parts, and complete metamorphosis




a plant that produces seed and dies at the end of its second year of growth (see annual, perennial)


having two flagella

Binary fission

a type of asexual reproduction in which two cells, usually of similar size and shape, are formed by the growth and division of one cell

Binomial, latin

the scientific name of an organism, composed of two names, the first designating the genus and second the specific epithet, together making the species name


having two nuclei


any test (assay) using a living organism


a compound toxic to all forms of life

Biocontrol (syn. Biological control)

use by humans of one species of organism to eliminate or control another species of organism

Biocontrol (syn. Biological control)

exploitation by humans of the natural competition, parasitism and/or antagonism of organisms for management of pests and pathogens

Biolistic transformation (see gene gun)

a method used for genetic engineering in which plant cells are bombarded with metal particles coated with foreign genes using a "gene gun"

Biological control (syn. Biocontrol)

exploitation by humans of the natural competition, parasitism and/or antagonism of organisms for management of pests and pathogens


the development of genetically modified organisms through the use of modern technology and processes, including genetic engineering


relating to life, as disease caused by living organisms

Biotroph (syn. Obligate parasite)

an organism that can live and multiply only on another living organism (see necrotroph)


a subdivision of a species, subspecies, or race based on some identifiable physiological trait such as a specific virulence pattern


having a double ascus wall (see unitunicate)


a symptom of plant disease characterized by shedding of unopened buds; classically, the failure to produce fruit or seed


sap flow from a wound


sudden, severe, and extensive spotting, discoloration, wilting, or destruction of leaves, flowers, stems, or entire plants


necrotic area of tissue irregular in form


insect or insect larva that forms tunnels or cavities in the bark or within the wood of trees

Boundary layer

the calm layer of air on surfaces below the layer of more turbulent air


a reduced leaf associated with a flower or inflorescence; modified leaf from the axil of which a flower arises


disease symptom, usually caused by a virus, involving addition or loss of flower color to create a variegated pattern. (see flower break)

Breeding line

plant strain used in a plant breeding program and usually containing one or more desirable agronomic or breeding characteristics

Broadcast application

application by spreading or scattering on the soil surface


profuse branching of woody stems from single stem position

Brown rot (of wood)

wood decay resulting from selective removal of cellulose and hemicellulose, leaving a brown amorphous residue that usually cracks into cubical blocks and consists largely of slightly modified lignin


a terminal or axillary structure on a stem consisting of a small mass of meristematic tissue, generally covered wholly or in part by modified scale leaves


a special type of plant grafting using a single bud on the rootstock of another plant; method of asexual reproduction in fungi, such as yeasts

Bud scale

a specialized protective leaf of a bud

Bud wood

wood consisting of strong, young shoots bearing buds suitable for use in budding


any insect of the order hemiptera characterized in part by piercing-sucking mouth parts, a triangular scutellum, two pairs of wings, and gradual metamorphosis


a short, flattened, usually globose or disc-shaped, underground, perennial, storage organ composed of concentric layers of overlapping fleshy scale leaves attached to a stem plate at the base; essentially a subterranean bud

Bunt ball

smut sorus filled, with teliospores, that replaces a cereal or grass kernel but is covered by plant tissue at maturity

Burr knot

a rough outgrowth, often present on the trunks or roots of certain trees


extension or flap of cuticle at the side of the male nematode sex organ, used for orienting during mating


plant with determinate growth


amorphous, hardened carbohydrate constituent of plant cell walls, commonly developing upon injury


specialized tissues that form over a wound or cut in a plant; cork cambium may form and the cells produced will gradually seal the wound


outermost flower whorl; sepals, collectively


a plant disease characterized (in woody plants) by the death of cambium tissue and loss and/or malformation of bark, or (in non-woody plants) by the formation of sharply delineated, dry, necrotic, localized lesions on the stem; "canker" may also be used to refer to the lesion itself, particularly in woody plants


the expanded leafy top of a plant or plants

Capsid (syn. Coat protein)

the protective layer of protein surrounding the nucleic acid core of a virus; the protein molecules which make up this layer


gel-like material surrounding a bacterial cell


any of various chemical compounds composed of carbon, hydrogen, and oxygen, such as sugars, starches, and cellulose

Carbon cycle

the continuous circulation of carbon atoms from inorganic carbon dioxide (co2) to organic molecules and back to co2


a substance or agent that causes cancer


the ovule-bearing structure of a flower in angiosperms


premature loss of abscised leaves or twigs


conelike cluster of male or female flowers; conelike fruit of angiosperms

Causal agent

organism or agent that incites and governs disease or injury

Cell membrane

structure that bounds a cell and helps control the movement of substances into and out of the cell

Cell wall

protective, resistant, but permeable structure secreted externally to the cell membrane in plants, bacteria, fungi, and certain other organisms


carbohydrate polysaccharide composed of glucose units; major component of plant primary cell wall

Center of origin

geographical area where a plant originated


the constricted portion of a chromosome to which, in mitosis, the chromosomal fiber is attached


seeds, propagative plant material, or nursery stock produced and sold under inspection to maintain genetic identity and purity, freedom from harmful pathogens, insect pests, and weed seeds. It is approved and certified by an official certifying agency.

Cfu (abbr. For colony forming unit)

the number of colonies formed per unit of volume or weight of a cell or spore suspension

Chemotaxis (syn. Chemotropism)

movement or growth of an organism in response to changing concentration of a chemical stimulus, often in relation to food or for mating


treatment of plant disease with chemicals (e.g. antibiotics or fungicides) absorbed and translocated internally

Chimera (or chimaera)

plant or organ consisting of two or more genetically different tissues


complex polysaccharide carbohydrate in fungal cell walls, animal exoskeletons, and nematode egg shells


thick-walled or double-walled asexual resting spore formed from hyphal cells (terminal or intercalary) or by transformation of conidial cells that can function as an overwintering stage

Chlorophyll (adj. Chlorophyllous)

one of a group of green pigments found in chloroplasts and important in photosynthesis


disklike structure containing chlorophyll in which photosynthesis occurs in green plants

Chlorosis (adj. Chlorotic)

failure of chlorophyll development, caused by disease or a nutritional disturbance; fading of green plant color to light green, yellow, or white


the structure that contains the genes of an organism; in eukaryotes, chromosomes are in the nucleus and can be visualized with an optical microscope as threads or rods during meiosis and mitosis; in bacteria, the chromosome is usually a single circle of dna that cannot be visualized with an optical microscope


pertaining to slow-developing, persistent, or recurring symptoms (see acute)

Chronic toxicity

poisoning due to low levels of exposure to a compound over a period of time (see acute toxicity)


a fungus group, also called the chytridiomycota, characterized by the production of motile zoospores and resting sporangia; the plant-pathogenic species are all biotrophs that are restricted to the cells of their host.

Circulative-propagative transmission(syn. Propagative transmission)

pathogen transmission characterized by a long period of acquisition of the pathogen (usually a mollicute, e.g. phytoplasma or spiroplasma, and sometimes a virus) by a vector (typically an insect), a latent period before the vector is able to transmit the pathogen, and retention of the pathogen by the vector for a long period because the pathogen reproduces or replicates in the vector

Circulative transmission (syn. Persistent transmission)

virus transmission characterized by a long period of acquisition of the virus by a vector (typically an insect), a latent period of several hours before the vector is able to transmit the virus, and retention of the virus by the vector for a long period, usually several days; the virus circulates in the body of the vector

Cirrhus (pl. Cirrhi)

a curled, tendril-like mass of exuded spores, held together by a slimy matrix

Clamp connection

a bridge- or buckle-hyphal protrusion in basidiomycetous fungi, formed at cell division and connecting the newly divided cells

Clavate (or claviform)


Cleistothecium (pl. Cleistothecia)

a spherical ascocarp that is closed at maturity


n. A population of cells or organisms of identical genotype; population of recombinant dna molecules all carrying the same inserted sequence;

v. The vegetative propagation of an organism to produce a population of identical individuals; the use of in vitro recombination techniques to insert a particular dna sequence into a vector


grow together into one body or spot

Coat protein (syn. Capsid)

the protective layer of protein surrounding the nucleic acid core of a virus; the protein molecules which make up this layer

Coccus (pl. Cocci)

a spherical (or near-spherical) bacterial cell


a particular sequence of three nucleotides in a nucleic acid that codes for a specific amino acid or termination of a polypeptide chain (see triplet codon)


a group of fungi in the deuteromycetes (imperfect fungi) that produce pycnidia or acervuli (see hyphomycetes)


having multiple nuclei embedded in cytoplasm without cross walls; nonseptate


the portion of the seedling or plant near the surface of the soil; in grafted woody plants, the scion portion of the plant near the soil surface


supporting tissue in soft stems and other plant parts, composed of elongated living parenchyma cells with unevenly thickened primary walls, often bordering veins in dicot leaves; the "strings" in celery


establishment and ramification of a pathogen within a host plant


to infect and ramify through plant tissue with the growth of a pathogen


growth of a microorganism in mass, especially as a pure culture

Colony forming unit (abbr. Cfu)

the number of colonies formed per unit of volume or weight of a cell or spore suspension

Companion cell

specialized cell adjacent to sieve tubes in phloem


isolation of a specific tissue area by host barrier tissues

Complete resistance

a resistant reaction in which some aspect of disease development, usually symptom expression or pathogen reproduction, is completely stopped (see partial resistance)


a mixture of organic residues and soil that is allowed to decompose biologically


one circle within another with a common center


the formation of asexual spores (conidia)


producing and bearing conidia

Conidioma (pl. Conidiomata)

specialized conidia-bearing structure, e.g. acervulus, pycnidium, sporodochium, synnema


simple or branched hypha on which conidia are produced

Conidium (pl. Conidia)

an asexual, nonmotile fungal spore that develops externally or is liberated from the cell that formed it


the temporary contact of bacterial cells during which genetic material is transferred


a shelf-like, typically hardened basidiocarp of a wood decaying fungus, usually a polypore


present or produced under all conditions (see induced)

Contact fungicide (syn. Protectant fungicide)

a fungicide that remains on the surface where it is applied; no after-infection activity (see systemic fungicide)

Continuous cropping

growing the same crop in the same location repeatedly


regrowth of woody plants by sprouts from stumps or roots

Coremium (pl. Coremia; syn. Synnema)

compact or fused, generally upright conidiophores, with branches and spores forming a headlike cluster


external protective tissue of a stem or root, impermeable to water and gasses; the primary component of bark


petals, collectively

Cortex (adj. Cortical)

region of parenchyma tissue between the epidermis and the phloem in stems and roots; region beneath the rind of a sclerotium


seed leaf, one in moncots and two in dicots; primary embryonic leaf within the seed in which nutrients for the new plant are stored

Crop rotation

the successive planting of different crop species; often used to improve soil fertility or to reduce disease and pest problems


a process in which sexual reproduction occurs as a result of the fusion of sex cells from different individuals (see self-fertilization)


transfer of pollen from the anthers to the stigma of another flower (see self-pollination)


the process whereby a normally susceptible host is infected with a less virulent pathogen (usually a virus) and thereby becomes resistant to infection by a second, usually related, more virulent pathogen


upper dome of tree, bearing leaves, flowers, and fruits; junction of root and stem of a plant, usually at the soil line; in grafted woody plants, the rootstock portion of the plant near the soil surface


the hook of an ascogenous hypha before ascus development; the curved apical portion of a blighted stem

Cryptobiosis (hidden life):

the ability to enter a state of suspended metabolic activity during unfavorable environmental conditions (drying, cold); survival strategy of some plant pathogenic nematodes


stem of grasses, cereals and bamboos


distoration, puffing, and crinkling of a leaf resulting from unequal growth

Cultivar (abbr. Cv.; syn. Variety)

a plant type within a species, resulting from deliberate genetic manipulation, which has recognizable characteristics (color, shape of flowers, fruits, seeds and height or form)

Cultural practices

the manner in which plants are grown, such as: application of nutrients, irrigation practices, type of cultivation; may be used for disease management


growth and propagation of microorganisms on nutrient media; growth and propagation of living plants

Cuticle (adj. Cuticular)

noncellular outer layer of an insect or a nematode; water-repellent, waxy layer of epidermal cells of plant parts, such as leaves, stems and fruit

Cv. (abbr. For cultivar; syn. Variety)

a plant type within a species, resulting from deliberate manipulation, which has recognizable characteristics (color, shape of flowers, fruits, seeds and height or form)


in fungi, a resting structure in a protective membrane or shell-like enclosure;

in nematode females, the egg-laden carcass of a female nematode;

in bacteria, a specialized type of bacterial cell enclosed in a thick wall, often dormant and resistant to environmental conditions


plant hormones (growth regulators) that control cell division and are important for shoot stimulation of callus in tissue culture


the study of changes induced by disease at the cellular level


living protoplasm in a cell, except the nucleus

Cytoplasmic inheritance (also extrachromosomal or maternal inheritance)

inheritance of genes not located in the nucleus, i.e. those in mitochondria and chloroplasts


death of a seedling before or shortly after emergence due to decomposition of the root and/or lower stem; it is common to distinguish between preemergence damping-off and postemergence damping-off

Days to harvest

term for the prescribed minimum number of days required by u.s. government regulations between a pesticide application and the harvest of the crop


the gradual decomposition of organic matter


describing a tree that sheds its leaves completely at the end of its annual growth period

Decoy crop

crop that stimulates germination of seeds of a parasitic plant such as witchweed (striga spp.), but is not susceptible to infection by the parasitic plant; helps reduce seed populations of the parasite in soil so a susceptible crop can be planted


loss of leaves from a plant, whether normal or premature


the departure of the average daily temperature from a defined base (e.g. the minimum recognized temperature for the growth of a plant species). The number of degree-days may be totaled to assess the accumulated warmth of a particular year's growing season.


opening by breaking into parts


a rust fungus that lacks the urediniospore (repeating) stage (e.g. many species of gymnosporangium) (see macrocyclic, microcyclic)



Deoxyribonucleicacid (abbr. Dna)

the double-stranded, helical molecule that contains genetic code information; each repeating unit, or nucleotide, is composed of deoxyribose (a sugar), a phosphate group, and a purine (adenine or guanine) or a pyrimidine (thymine or cytosine) base


to dry out


ceasing vegetative growth when the first flower or reproductive structure forms

Deuteromycetes (syn. Fungi imperfecti)

group of fungi without a sexual stage; the asexual stage of ascomycetes and basidiomycetes

Diagnostic (n. Diagnosis)

a distinguishing characteristic important for the identification of a disease or other condition


a period of spontaneous dormancy, independent of environmental conditions, interrupting developmental activity in an embryo, larva or pupa


branching, often successively, into two more or less equal arms

Dicot (syn. Dicotyledon)

plant with two cotyledons or seed leaves (see monocot)

Dieback (v. Die back)

progressive death of shoots, leaves, or roots, beginning at the tips

Differential host (syn. Differential cultivar)

a plant host that on the basis of disease symptoms serves to distinguish between various strains or races of a given plant pathogen

Differential medium

culture medium that is used to distinguish between organisms that can grow on it


the physiological and morphological changes that occur in a cell, tissue, or organ during development from a juvenile state to a mature state


having lobes radiating from a common center

Dikaryon (adj. Dikaryotic)

having two sexually compatible haploid nuclei per cell, that divide simultaneously; this phase is called the dikaryophase

Dilution plating

a method to obtain pure colonies of bacteria and fungi in which infected plant material or infested soil is diluted in sterilized water. Small samples of the water are spread on the medium surface of several petri plates to find which dilution will produce pure colonies.

Dilution streaking

repeated streaking of bacteria on the surface of a nutrient medium with a sterile metal loop to allow pure colonies to grow


having two distinct shapes or forms


having male and female reproduction structures on separate individuals (see monoecious)


having two complete sets of chromosomes (2n chromosomes) (see haploid, polyploid)

Direct penetration

penetration of plant tissues by a pathogen through barriers such as leaf cuticle by chemical and physical means (e.g. penetration peg)


a group of the ascomycetes in which the hymenium is exposed at maturity; one in which the fruiting body is an apothecium or discocarp


abnormal functioning of an organism

Disease cycle

succession of all of events and interactions among the host, parasite and environment that occur in a disease, from initial infection of the plant by a causal agent, through pathogenesis, to over-seasoning, until another infection occurs

Disease incidence

number of plants affected by a disease within a population

Disease progress curve

graph of some measure of disease (i.e. severity) over time

Disease pyramid

a memory aid similar to the disease triangle but including, in addition, the factor of time in the development of a disease

Disease severity

the measure of damage done by a disease

Disease triangle

a memory aid that diagrams the three important components necessary for disease: susceptible plant, virulent pathogen and favorable environment


to eliminate a pathogen from infected plant tissues


to kill pathogens that have not yet initiated disease, or other contaminating microoganisms, that occur in or on inanimate objects as such soil or tools, or that occur on the surface of plant parts such as seed

Dispersal (syn. Dissemination)

spread of infectious material (inoculum) from diseased to healthy plants

Dissemination (syn. Dispersal)

spread of infectious material (inoculum) from diseased plants to healthy plants


far from the point of attachment or origin; in a direction away from main body (see proximal)

Dna (abbr. For deoxyribonucleic acid)

the double-stranded, helical molecule that contains genetic code information; each repeating unit, or nucleotide, is composed of deoxyribose (a sugar), a phosphate group, and a purine (adenine or guanine) or a pyrimidine (thymine or cytosine) base


parasitic seed plant (cuscuta spp.) Without leaves; a yellow filamentous vine

Dolipore septum

cross wall found in basidiomycetes and characterized by special swellings and membranes in association with the septal pore


describes a phenotypic trait that is expressed in hybrid progeny of diploid organisms even when contributed by only one of the parents (see recessive)

Dormancy (adj. Dormant)

a condition of suspended growth and reduced metabolism of an organism, generally induced by internal factors or environmental conditions as a mechanism of survival

Downy mildew

a plant disease in which the fungus appears as a downy growth on the host surface; caused by a member of the oomycetes

Drift (of pesticides)

movement of airborne particles of a spray, dust, or vapor away from the target area during or shortly after an application


insufficient soil water for normal plant growth

Durable resistance

resistance that remains effective during prolonged and widespread use in an environment favorable to disease


underdevelopment of a plant or plant organs, which may be caused by disease, inadequate nutrition, or unfavorable environmental conditions


having small spines projecting from cell walls


the study of the interactions that occur between individual organisms, groups of organisms and organisms and their environment

Economic threshold

the pathogen density at or above which the value of crop losses (in the absence of management efforts) would exceed the cost of management practices


community of living things and their environment

Ectomycorrhiza (pl. Ectomycorrhizae)

symbiotic association between a nonpathogenic or weakly pathogenic fungus and the roots of plants with fungal hyphae between and external to root cells (see arbuscular mycorrhiza)


parasite that feeds from the exterior of its host (see endoparasite)


fungal development primarily over the root surface

Edema (also oedema; syn. Intumescence)

blisters produced on leaves and other plant parts under conditions of high moisture and restricted transpiration

Egg mass

group of eggs held together by a gelatinous matrix

Electron microscope

microscope that uses a focused beam of electrons to produce a greatly enlarged image of minute objects, such as a virus, in the same way that light is used in a compound microscope


a molecule produced by the host (or pathogen) that induces a response by the pathogen (or host)

Elisa (acronym for enzyme-linked immunosorbent assay)

a serological test in which the sensitivity of the reaction is increased by attaching an enzyme that produces a colored product to one of the reactants


an organism in the early stages of development, such as a young plant in the seed, or a nematode before hatching from the egg


growth of the seedling shoot through the surface of the soil


abnormal outgrowth from the surface of a stem or leaf


to cover virus nucleic acid with a protein coat


to form a cyst or protective covering


native to a particular place; pertaining to a low and steady level of natural disease occurrence


inner layer of a fruit wall

Endoconidium (pl. Endoconidia)

a conidium produced inside a hypha or conidiophore


layer of cells within the root, between the vascular tissue and the cortex


arising from the inside (see exogenous)

Endomycorrhiza (pl. Endomycorrhizae; syn. Arbuscular mycorrhiza)

symbiotic association between a nonpathogenic or weakly pathogenic fungus and the roots of plants in which fungal hyphae invade cortical cells of the root (see ectomycorrhiza)


parasitic organism that lives and feeds from inside its host (see ectoparasite)


plant developing inside another organism; also used for endoparasitic fungi found in grass species

Endoplasmic reticulum

system of interconnected cytoplasmic membranes that transports materials within the cell


nutritive tissue formed within the embryo sac of seed plants


resistant, thick-walled asexual spore formed within a bacterial or fungal cell


protein that catalyzes a specific biochemical reaction

Enzyme-linked immunosorbent assay (acronym elisa)

a serological test in which the sensitivity of the reaction is increased by attaching an enzyme that produces a colored product to one of the reactants

Epa (acronym for environmental protection agency)

the federal agency responsible for controlling the various aspects of air, water, and soil pollution, including pesticide regulations


portion of the stem of a plant embryo or seedling above the node where the cotyledons are attached (see hypocotyl)


an increase of disease in a population; a general and serious outbreak of disease (see epiphytotic)

Epidemiology (adj. Epidemiologic)

the study of factors influencing the initiation, development, and spread of infectious disease; the study of disease in populations of plants

Epidermis (adj. Epidermal)

surface layer of cells of leaves and other plant parts


abnormal, downward curling of a leaf, leaf part, or stem


living on the surface of plants, but not as a parasite


an epidemic in a plant population


on the upper surface of a leaf


organism growing on a plant surface, but not as a parasite


an amino acid (or other) sequence that effects formation of an antibody

Eps (extracellular polysaccharides)

sugar polymers that contribute to the slimy appearance of bacteria probably promote colonization of plant tissues and disease development in bacteria


control of plant disease by eliminating the pathogen after it is established or by eliminating the plants that carry the pathogen


a disease of certain grasses and cereals, especially rye, caused by claviceps spp.;


a sclerotium, or resting structure, produced by claviceps species and other closely related fungi in infected flowers of parasitized grain plants


a disease caused by ingestion of grain contaminated with alkaloids of ergot fungi, often called the holy fire or st. Anthony's fire in the middle ages


bursting or erupting through the substrate surface


failure of inherently susceptible plants to become diseased, even though disease is prevalent


a plant hormone influencing various aspects of vegetative growth, fruit ripening, abscission of plant parts, and the senescence of flowers


elongation of stems caused by reduced light intensities


the study of the causes of diseases


an organism containing a membrane-bound nucleus and other organelles, i.e. all higher plants, animals, fungi, and protists (see prokaryote)


control of disease by excluding the pathogen or infected plant material from crop production areas (e.g. by quarantines and embargoes)


originating from the outside (see endogenous)

Extracellular polysaccharides (eps)

outside a cell

Extrachromosomal inheritance(also cytoplasmic or maternal inheritance)

sugar polymers that aid in movement, help prevent desiccation, and contribute to the slimy appearance of bacteria, fungi, and nematodes; and probably promote colonization of plant tissues and disease development in bacteria


inheritance of genes not located in the nucleus, i.e. those in mitochondria and chloroplasts

F. Sp. (abbr. For forma specialis)

liquid excreted or discharged from diseased tissues, from roots and leaves, or by fungi


a taxonomic group within a pathogenic species defined in terms of host range, i.e. members of different formae speciales infect different groups of plants

Facultative parasite

capable of changing life-style, e.g. from saprophytic to parasitic or the reverse

Facultative saprophyte

organism that is normally saprophytic but is capable of being parasitic


organism that is normally parasitic but is capable of being saprophytic


cultivated land kept free from a crop or weeds during the normal growing season

Fascicle (adj. Fasciculate)

malformation in shoots or floral organs manifested as enlargements and flattening as if several parts were fused


small group, bundle, or cluster

Feeder root

in reference to prokaryotic organisms, having special growth and nutritional requirements


fine root that absorbs water and dissolved nutrients

Ffdca (acronym for federal food, drug, and cosmetic act)

oxidation of certain organic substances in the absence of molecular oxygen


the federal law which sets legal tolerances of pesticides on food products at harvest

Fifra (acronym for federal insecticide, fungicide, and rodenticide act)

elongated plant cell with thick walls (in xylem and phloem), dead at maturity

Filamentous(syn. Filiform)

the federal law which legislates the conditions for use of pesticides




form of cell division in prokaryotes; the ability of an organism to survive and reproduce; the ability of an organism to pass its genes to the next generation


wilted, lacking turgor


isolated, wilted or necrotic branch with dead leaves attached

Flagellum (pl. Flagella)

hairlike, whiplike, or tinsel-like appendage of a motile cell, bacterium or zoospore that provides locomotion


minute, discolored spot in green tissue


having turns or windings; capable of bending

Flower break

break or stripe in flower color (see breaking)

Focus (pl. Foci)

small area of diseased plants within a population


pertaining to leaves

Forest decline

combination of biotic factors (e.g. insect pests, pathogens) and abiotic factors (e.g. drought, air pollution) that contributes to poor growth and death of populations of trees

Form genus

a genus based on morphology and not on evolutionary relationships, such as used for imperfect fungi

Forma specialis (abbr. F.sp.; pl. Formae speciales)

a taxonomic group within a pathogenic species defined in terms of host range, i.e. members of different formae speciales infect different groups of plants

Fqpa (acronym for food quality protection act)

the federal law which sets a health-based standard governing pesticide tolerance levels in food

Free water

unbound water; often used to describe a film of water on a plant surface


general term for spore-bearing organs in both macro- and microfungi

Fruiting body

any of various complex, spore-bearing fungal structures

Fumigant (v. Fumigate)

a gas or volatile substance used to kill or inhibit the growth of microorganisms or other pests

Fungi imperfecti (syn. Deuteromycetes)

group of fungi without a sexual stage; also, the asexual stage of ascomycetes and basidiomycetes

Fungicide (adj. Fungicidal)

chemical or physical agent that kills or inhibits the growth of fungi

Fungus (pl. Fungi)

a eukaryotic organism that is usually filamentous (forming a mycelium) and heterotrophic, has cell walls composed of chitin, and reproduces by sexual and/or asexual spores

Fungistat (adj. Fungistatic)

a chemical or physical agent that inhibits fungal growth, sporulation, or spore geminiation, but does not cause death


inhibition of fungal growth, sporulation, or spore germination but not death; used to describe the nonspecific phenomenon in natural soils where spore germination is inhibited and often overcome by rhizosphere nutrients


spindle-shaped; tapering at each end

Gall (syn. Tumor)

abnormal swelling or localized outgrowth, often roughly spherical, produced by a plant as a result of attack by a fungus, bacterium, nematode, insect, or other organism


insect tunnel in bark and wood

Gametangium (pl. Gametangia)

cell containing gametes or nuclei that act as gametes


sex cell


the haploid stage of a plant (see sporophyte)


unit within an organism controlling heritable characteristics; genes are organized on chromosomes

Gene gun (see biolistic transformation)

a device used to bombard plant cells with metal particles coated with foreign genes to accomplish genetic engineering

Gene-for-gene hypothesis

the hypothesis that corresponding genes for resistance and virulence exist in the host and pathogen, respectively

General resistance (syn. Horizontal resistance, race non-specific resistance)

resistance that is effective against all biotypes of the pathogen (see durable resistance, specific resistance, vertical resistance)


relating to heredity; referring to heritable characteristics

Genetic code

the system of triplet codons composed of nucleotides of dna or rna that determine the amino acid sequence of a protein

Genetic engineering

the transfer of specific genes between organisms using enzymes and laboratory techniques rather than biological hybridization

Genetically modified organism; (gmo) (syn. Transgenic)

organism possessing a gene from another species; used to describe the organisms that have been the subject of genetic engineering


the complete genetic information of an organism or virus


genetic constitution of an individual or group; class or group of individuals sharing a specific genetic makeup (see phenotype)

Genus (pl. Genera)

a taxonomic category that includes a group of closely related (structurally or phylogenetically) species; the genus or generic name is the first name in a latin binomial


fruit that ripens beneath the ground (e.g. peanut pod)

Germ theory

the theory that infectious or contagious diseases are caused by microorganisms (germs)

Germ tube

hypha resulting from an outgrowth of the spore wall and cytoplasm after germination

Germinate (n. Germination)

begin growth (as of a seed, spore, sclerotium, or other reproductive body)


bearer of heredity material, often loosely applied to cultivars and breeding lines

Giant cell

enlarged, multinucleate cell formed in roots by repeated nuclear division without cell division induced by secretions of certain sedentary plant-parasitic nematodes


plant hormones (growth regulators) that affect stem elongation


thin, radial membrane producing basidiospores in the cap of certain basidiomycetous fungi (e.g. mushrooms)


to circle and cut through a stem or the bark and outer few rings of wood, disrupting the phloem and xylem


smooth; without hairs


a substance that, on decomposition, yields glucose and certain other compounds; some glucosides are defense compounds produced by plants, e.g. cyanogenic or phenolic glucosides


sexual structure in animals that produces gametes


transfer of aerial parts of one plant (e.g. buds or twigs - the scion) into close cambial contact with the root or trunk (the rootstock) of a different plant; a method of plant propagation; the joining of cut surfaces or growing roots of two plants to form a living union

Graft transmission

transmission of a pathogen from one host plant to another through fusion of living tissue from the diseased host with living tissue of a healthy host


bacteria staining red or pink in the gram staining procedure after treatment with gram's stain


bacteria staining violet or purple in the gram staining procedure after treatment with gram's stain

Gram stain

procedure used for identification of bacteria in which crystal violet stain, gram's iodine, ethyl alcohol and safranin stain are applied in succession to cells of the bacteria


containing an egg or eggs; capable of depositing eggs

Green manure

a crop plowed under while still green and growing to improve the soil; sometimes used to enhance populations of antagonistic microorganisms for biological control

Growth regulator (syn. Hormone)

a chemical substance produced in one part of an organism and transported in minute quantities to induce a growth response in another part, e.g. in plants, auxins, cytokinins, and gibberellins

Guard cells

paired, specialized, epidermal cells that contain chloroplasts and surround a stoma


gelatinous, sugary aggregate that is synthesized and exuded by plant tissues

Gummosis (pl. Gummoses)

pathologic condition characterized by excessive formation of gums; the products of cell degeneration


exudation of watery, sticky liquid from hydathodes, especially along leaf margins


a place with a particular kind of environment suitable for the growth of an organism


having a single complete set of chromosomes (see diploid, polyploid)


ability to withstand stress


stem or stalks collectively

Haustorium (pl. Haustoria)

specialized branch of a parasite formed inside host cells to absorb nutrients


in plants, a type of inflorescence in which numerous small flowers are densely crowded on a disk or around a central stalk


central cylinder of nonfunctional xylem in a woody stem (see sapwood)


parasitic flowering plant that contains chlorophyll when mature (photosynthetic) and obtains water with dissolved nutrients by connecting to the host xylem via the haustorium, e.g. true mistletoe (phoradendron spp. Or viscum spp.) Or witchweed (striga spp.)


describing primary, soft, nonwoody tissue, as a plant or plant part; having the characteristics of an herb


a chemical used for killing plants or inhibiting plant growth, e.g. a weed or grass killer


a measure of the ability of a characteristic to be passed from one generation to the next

Hermaphrodite (adj. Hermaphroditic)

having both male and female reproductive organs


pertaining to a rust fungus requiring two unrelated host plants for completion of its life cycle (see autoecious)

Heterokaryon (adj. Heterokaryotic)

cell with genetically different nuclei

Heterosis (syn. Hybrid vigor)

increased vigor of hybrid offspring when compared to either parent

Heterothallism (adj. Heterothallic)

condition in which sexual reproduction can occur only in the presence of genetically different mycelia (see homothallism)


an organism that obtains nourishment from outside sources and must obtain its carbon from organic carbon compounds (see autotroph)


having alternate forms (allele) of a gene on homologous chromosomes (see homozygous)


the whole fungus in all its states (see anamorph, teleomorph)


parasitic flowering plant that lacks chlorophyll (nonphotosynthetic) and must rely totally on the contents of the xylem and the phloem of the host plant, e.g. broomrape (orobanche spp.)

Homothallism (adj. Homothallic)

condition in which sexual reproduction occurs with a single thallus; self-fertile (see heterothallism)


having the same form (allele) of a gene on homologous chromosomes (see heterozygous)


sugary ooze or exudate, often from aphids, and a characteristic symptom of ergot

Horizontal resistance (syn. General resistance, race non-specific resistance)

resistance which is effective against all biotypes of the pathogen (see durable resistance, specific resistance, vertical resistance)

Hormone (syn. Growth regulator)

a chemical substance produced in one part of a an organism and transported in minute quantities to induce a growth response in another part, e.g. in plants, auxins, cytokinins, and gibberellins

Host plant

living plant attacked by or harboring a parasite or pathogen and from which the invader obtains part or all of its nourishment

Host range

the range of plants on which an organism, particularly a parasite, feeds


transparent or nearly so; translucent; often used in the sense of colorless

Hybrid (v. Hybridize)

offspring of two individuals of different genotypes

Hybrid vigor (syn. Heterosis)

increased vigor of hybrid offspring when compared to either parent


a cell produced by the fusion of an antibody-producing cell and a lymphoma (cancer) cell for production of monoclonal antibodies


epidermal leaf structure specialized for secretion or exudation of water; leaf opening at terminus of vein

Hydrogen fluoride (hf)

a common pollutant from volcanoes and several industries such as brick factories, aluminum smelters, and phosphate fertilizer factories.


continuous, spore-bearing layer of a fungus fruiting body


organism that is parasitic upon another parasite

Hyperplasia (adj. Hyperplastic)

abnormal increase in the number of cells, often resulting in the formation of galls or tumors


extremely or excessively sensitive; often refers to an extreme reaction to a pathogen

Hypersensitive reaction and pathogenicity (hrp) gene

gene required for elicitation of the hypersensitive (hr) response in resistant plants and causation of disease in susceptible plants; a type of avirulence gene

Hypersensitive response (hr)

rapid and localized cell death at the site of infection in resistant interactions between plants and pathogens

Hypertrophy (adj. Hypertrophic)

abnormal increase in the size of cells in a tissue or organ, often resulting in the formation of galls or tumors

Hypha (pl. Hyphae; adj. Hyphal)

single, tubular filament of a fungal thallus or mycelium; the basic structural unit of a fungus

Hyphal sheath (syn. Mantle)

dense hyphal mass of ectomycorrhizal fungus enclosing the short feeder roots of plants


imperfect fungi that produce conidia freely or on a sporodochium or synnema (see coelomycetes)


stalked, thick-walled, lobed cells that stick to plant surfaces; sometimes used to describe the infection structures produced by ectotrophic hyphae of certain root-infecting fungi such as gaeumannomyces (take-all pathogen)


portion of the stem below the cotyledons and above the root (see epicotyl)


reduced ability to cause disease

Icosahedral (n. Icosahedron)

having 20 faces, as a polyhedral-shaped virus particle (see isometric)


cannot be infected by a given pathogen


a detection method based on antibodies specifically selected to react with the substance to be detected (the antigen)


chemical or activity that suppresses the natural immune responses in animals, including humans

Imperfect fungi (syn. Fungi imperfecti, deuteromycetes)

group of fungi without a sexual stage; also, the asexual stage of ascomycetes and basidiomycetes

Imperfect state (syn. Anamorph)

the asexual form in the life cycle of a fungus, when asexual spores (such as conidia) or no spores are produced

In planta

in a plant

In situ

in its original place or environment

In vitro

in glass, on artificial media, or in an artificial environment; outside the host

In vivo

within a living organism

Inclusion body

structure developed within a plant cell as a result of infection by a virus, often useful in identifying the virus

Incomplete dominance

the interaction of alleles of a gene that produces an intermediate phenotype, as in the production of pink flowers when red and white alleles are present in a heterozygous individual

Incubation period

the time between penetration of a host by a pathogen and the first appearance of disease symptoms; the time during which microorganisms inoculated onto a medium are allowed to grow


pertaining to fruit that does not split open at maturity


continuing to grow vegetatively while producing flowers or reproductive structures


testing of a plant for infection, often by mechanical transmission or by grafting tissue from it to an indicator plant

Indicator plant

plant that reacts to a pathogen or an environmental factor with specific symptoms, used to detect or identify the pathogen or determine the effects of the environmental factor

Indirect penetration

penetration of plant tissues by a pathogen through natural openings (e.g. stomata) or wounds


produced in response to a stimulus (see constitutive)

Induced systemic resistance (isr)

reduced disease symptoms on a portion of a plant distant from the area where the inducing agent is active, caused by the triggering of active plant defenses against a variety of pathogens; used to describe increased resistance in plants induced by certain rhizobacteria (see systemic acquired resistance- sar)


process in which an organism enters, invades, or penetrates and establishes a parasitic relationship with a host plant

Infection court

site in or on a host plant where infection can occur

Infection cushion

organized mass of hyphae formed on the surface of a plant from which numerous infective hyphae develop

Infection focus

initial site of infection, generally with reference to a population of plants

Infection peg (syn. Penetration peg)

the specialized, narrow, hyphal strand on the underside of an appressorium that penetrates host cells

Infection period

the time required for infection to occur under conducive environmental conditions, usually hours of leaf wetness and temperature


pertaining to disease, capable of spreading from plant to plant


referring to an organism able to attack a host and cause infection; referring to a vector carrying or containing a pathogen and able to transfer it to a host plant

Infest (n. Infestation)

to attack as a pest (used especially of insects and nematodes); to contaminate, as with microorganisms; to be present in large numbers


flower or flower cluster

Initial inoculum (syn. Primary inoculum)

inoculum, usually from an overwintering source, that initiates disease in the field, as opposed to inoculum that spreads disease during the season


damage caused by transitory interaction with an agent such as an insect, chemical, or unfavorable environmental condition

Inner bark

interior, living portion of the bark; secondary phloem

Inoculate (n. Inoculation)

to place inoculum in an infection court; to insert a pathogen into healthy tissue

Inoculum (pl. Inocula)

pathogen or its parts, capable of causing infection when transferred to a favorable location

Inoculum density

a measure of the number of propagules of a pathogenic organism per unit area or volume


member of the class hexapoda (phylum arthropoda) possessing three sets of limbs attached to a central body segment


one of the stages of growth between molts, in the life history of certain insects

Integrated pest management (abbr. Ipm)

a combination of strategies to reduce losses due to pests and pathogens based on environmental and economic considerations


between or among cells


to grow two or more crops simultaneously on the same area of land

Internode (adj. Internodal)

the portion of a stem between two successive nodes

Internal transcribed spacers

regions of a dna sequence that separate genes for certain ribosomal rnas (rrnas). These genes appear to be nearly identical among a wide variety of species, but the dna spacers between them are quite variable and may be species-specific. This makes them good potential targets for "primers" for polymerase chain reaction (pcr) amplification that is used to identify a wide variety of organisms.


between (leaf) veins


through or within cells

Intumescence (syn. Edema or oedema)

blisters produced on leaves and other plant parts under conditions of high moisture and restricted transpiration

Ipm (abbr. For integrated pest management)

a combination of strategies to reduce losses due to pests and pathogens based on environmental and economic considerations


(n.) A culture or subpopulation of a microorganism separated from its parent population and maintained in some sort of controlled circumstance;


(v.) To remove from soil or host material and grow in pure culture

Its (acronym for internal transcribed spacers)

usually used for virus particles to describe those that are icosahedral in structure and appear approximately round


regions of a dna sequence that separate genes for certain ribosomal rnas (rrnas). These genes appear to be nearly identical among a wide variety of species, but the dna spacers between them are quite variable and may be species-specific. This makes them good potential targets for "primers" for polymerase chain reaction (pcr) amplification that is used to identify a wide variety of organisms


an immature form that appears similar to but usually smaller than the adult and is not sexually mature (e.g. insects with gradual metamorphosis, nematodes)

Koch's postulates

the fusion of nuclei


the procedure used to prove the pathogenicity of an organism, i.e. its role as the causal agent of a disease


gall; localized abnormal swelling

Land race

expanded part of a leaf (see petiole)

Larva (pl. Larvae)

plant stocks selected by farmers on a local basis over many years


immature stage of certain animals (especially insects) that undergo complete metamorphosis; the wormlike or caterpillar stage of the life cycle of such insects

Latent infection

present but not manifested or visible, as a symptomless infection by a pathogen

Latent period

infection unaccompanied by visible symptoms

Lateral bud (syn. Axillary bud)

the time between infection and the production of new inoculum; the time after a vector has acquired a pathogen and before it can be transmitted

Ld50 (abbr. For lethal dose 50%)

bud that develops in the axil of a leaf

Leaf dip

a measure of relative acute toxicity; the lethal dose of a compound that causes death in 50% of the test animals treated

Leaf sheath

inspection of a sample of sap from a suspected virus-infected leaf using an electron microscope

Leaf spot

lower, tubular part of a grass leaf that clasps the culm


a plant disease lesion typically restricted in development in the leaf after reaching a characteristic size


mobile insects with sucking mouthparts (order homoptera)


one of the separate blades or divisions of a compound leaf


disease symptom in which the edges of the leaf roll or turn up; often a symptom of virus infection

a plant of the family fabaceae (formerly leguminosae)

simple, dry, dehiscent fruit developed from a simple pistil and splitting at maturity along two seams;


a natural opening in the surface of a stem or tuber, fruit or root for gas exchange


localized diseased area or wound

Life cycle

the cyclical stages in the growth and development of an organism


hardening of tissue through the deposition of lignin in the cell wall


complex organic substance or group of substances that impregnate the cell walls of xylem vessels and certain other plant cells; constitutes wood

Local lesion

small, restricted lesion, often the characteristic reaction of differential cultivars to specific pathogens, especially in response to mechanical inoculation with a virus


to fall over

Lumen (pl. Lumina)

central cavity of a cell or other structure


to cause disintegration of tissues by separation of cells; to soften by soaking

Macroconidium (pl. Macroconidia)

the larger of two kinds of conidia formed by certain fungi (see microconidium)


a rust fungus that typically exhibits all five stages of the rust life cycle (see demicyclic, microcyclic)


an element needed in relatively large quantities for plant growth, e.g. nitrogen (n), phosphorus (p), and potassium (k); (see micronutrient)

Mantle (syn. Hyphal sheath)

dense hyphal mass of ectomycorrhizal fungus enclosing the short feeder roots of plants

Marker-assisted selection

a procedure used in plant breeding in which genetic markers that are (a) easy to identify and (b) linked to desirable genetic traits that are difficult to identify (such as disease resistance) are used to aid in selection from a population

Maternal inheritance (also cytoplasmic or extrachromosomal inheritance)

inheritance of non-nuclear genes, i.e. those in mitochondria and chloroplasts

Mating types

compatible strains, usually designated + and - or a and b, necessary for sexual reproduction in heterothallic fungi

Mechanical injury

injury of a plant part by abrasion, mutilation, or wounding

Mechanical transmission

spread r introduction of inoculum to an infection court (wounding) by human manipulation, accompanied by physical disruption of host tissues

Medium (pl. Media)

a mixture of organic and/or inorganic chemical compounds and water that provides the nutrients needed for the growth of a microorganism in vitro; for higher plants, a mixture of fertilizers and other components in which a plant is growing


process of nuclear division in which the number of chromosomes per nucleus is halved, i.e. converting the diploid state to the haploid state (see mitosis)


brown-black pigment; common in sclerotia and other survival structures

Meristem (adj. Meristematic)

plant tissue characterized by frequent cell division, producing cells that become differentiated into specialized tissues

Meristem culture

aseptic in vitro culture of a plant or plant part from a portion of the meristem; a method used to produce pathogen-free plants

Messenger rna (abbr. Mrna)

a form of rna that carries information to direct the synthesis of protein


any chemical participating in metabolism; a nutrient


pertaining to or relating to microbes, or microorganisms


weather conditions on a small scale, e.g. at the surface of the plant or within a crop

Microconidium (pl. Microconidia)

the smaller of two kinds of conidia formed by certain fungi (see macroconidium)


describing a rust fungus that produces only teliospores and basidiospores (see demicyclic, macrocyclic)


the combination of all microorganisms in a particular environment

Micron (syn. Micrometer)

one millionth of a meter


an essential element needed by plants for growth and required in very small amounts (see macronutrient)

Microorganism (syn. Microbe)

an organism of such small size that it can only be seen as an individual organism with the aid of microscope


microscopic, dense aggregate of darkly pigmented, thick-walled hyphal cells

Middle lamella

the layer, consisting largely of pectic substances, between the walls of adjacent plant cells


central, thickened vein of a leaf


migrating from place to place on a plant or from plant to plant when feeding (see sedentary)


thin coating of mycelial growth and spores on the surfaces of infected plant parts

Mitochondrion (pl. Mitochondria)

cellular organelle outside the nucleus that functions in respiration


nuclear division in which the chromosome number remains the same (see meiosis)

Mlo (syn. Mycoplasmalike organsim)

archaic term for phytoplasma; plant-parasitic pleomorphic mollicute (prokaryote with no cell wall) found in phloem tissue; cannot yet be grown on artificial nutrient media


any microfungus with conspicuous, profuse, or woolly superficial growth (mycelium and/or spore masses) on various substrates; especially an economically important saprobe; molds commonly grow on damp or decaying matter and on the surface of plant tissues


one of a group of prokaryotic organisms bounded by flexuous membranes and lacking cell walls (see phytoplasma and spiroplasma)


to shed a cuticle or body encasement during a phase of growth

Monoclonal antibody

antibody produced from clones of a single antibody-producing cell (see polyclonal antibody)

Monocot (syn. Monocotyledon)

plant with one cotyledon, such as grasses, grain crops, corn (see dicot)


the growth of the same plant species in close proximity, with few or no other types of plant present


having one disease or life cycle per growing season (see polycyclic)


having male and female reproductive organs on a single individual (see dioecious)


determined by a single gene (see polygenic)

Monogenic resistance (syn. Single gene resistance)

resistance conferred by a single gene (see oligogenic resistance, multigenic resistance, polygenic resistance)

Monoxenic culture

a culture containing one species of organism growing in the presence of one other species of organism

Morphology (adj. Morphologic)

the study of the form of organisms; form and structure of organisms


disease symptom characterized by non-uniform coloration, with intermingled normal, light green and yellowish patches, usually caused by a virus; often used interchangeably with mottle


capable of self-propulsion by means of flagella, cilia, or amoeboid movement


disease symptom comprising light and dark areas in an irregular pattern, usually caused by a virus; often used interchangeably with mosaic

Movement protein

for viruses, a protein encoded by the pathogen that is required for spread within an infected plant

Mrna (abbr. For messenger rna)

a form of rna that carries information to direct the synthesis of protein


viscous, slimy


layer of material, such as organic matter or plastic, applied to the surface of the soil for purposes such as retention of water and inhibition of weeds


composed of many cells (see unicellular)

Multigenic resistance (syn. Polygenic resistance)

resistance conferred by several genes (see monogenic resistance, oligogenic resistance, single gene resistance)


mixture of cultivars that differ only in single, major genes for resistance to a pathogen, giving the opportunity to modify the mixture from year to year as needed


having more than one nucleus per cell (see uninucleate)

Multiparticulate virus

plant virus in which the genome is divided into more than one piece of nucleic acid, which are encapsidated in more than one particle

Multipartite virus

plant virus in which the genome is divided into more than one piece of nucleic acid


having many septa or crosswalls


a dried shriveled fruit; plant part or organ partially or completely replaced with fungal structures


a fleshy fruiting body of a fungus, especially of a basidiomycete of the family agaricaceae


a substance that causes a mutation

Mutation (n.mutant)

an abrupt heritable or genetic change in a gene or an individual as a result of an alternation in a gene or chromosome, or of an increase in chromosome number

Mycelia sterilia

a group in the fungi imperfecti that does not produce spores, but may produce chlamydospores or sclerotia, e.g. rhizoctonia and sclerotium; subsequent research has defined sexual reproduction for some species

Mycelium (pl. Mycelia, adj. Mycelial)

mass of hyphae constituting the body (thallus) of a fungus


the study of fungi


a fungus that attacks another fungus

Mycoplasmalike organism (syn. Mlo)

archaic term for phytoplasma; plant-parasitic pleomorphic mollicute (prokaryote with no cell wall) found in phloem tissue; cannot yet be grown on artificial nutrient media

Mycorrhiza (pl. Mycorrhizae; adj. Mycorrhizal)

symbiotic association between a nonpathogenic or weakly pathogenic fungus and the roots of plants (see ectomycorrhiza and endomycorrhiza)


poisonous compound produced by a fungus


a virus that infects fungi

Myxomycetes (syn. Slime molds)

saprophytic organisms that form vegetative amoeboid plasmodia and spores

Necrosis (adj. Necrotic)

death of cells or tissue, usually accompanied by black or brown darkening


a parasite that typically kills and obtains its energy from dead host cells (see biotroph)


a nectar-secreting gland in a flower

Needle cast (of conifers)

disease symptom caused by fungi resulting in premature drop of needles

Negative sense rna

ribonucleic acid complimentary to the positive or plus sense; not translated into protein (see positive sense rna)


agent, usually a chemical, that kills nematodes


nonsegmented roundworm (animal), parasitic on plants or animals, or free living in soil or water

Nitrogen cycle

the cycling of the element nitrogen from gaseous forms to various inorganic forms, such as ammonium, nitrates and nitrites, and organic forms, such as nucleic acids and proteins and back to elemental nitrogen

Nitrogen fixation

the conversion of gaseous n2 to a form available for plant uptake

Nitrogen oxides

primary air pollutants produced from internal combustion engines and other industrial processes

Node (adj. Nodal)

enlarged portion of a shoot at which leaves or buds arise

Nodule (v. Nodulation)

small knot or irregular, rounded lump; on leguminous plants, structures on roots that contain nitrogen-fixing bacteria


the scheme by which names are attached to objects, including organisms

Noninfectious disease

a disease that is caused by an abiotic agent that cannot be transmitted from one plant to another

Nonpathogenic (syn. Avirulent)

unable to cause disease

Nonpersistent transmission (syn. Stylet-borne transmission)

a type of virus transmission in which the virus is acquired and transmitted by the vector after short feeding times, and is retained by the vector for only a short period of time


without cross-walls; coenocytic


a cultural system most often used with annual crops, in which the new crop is seeded or planted directly in a field on which the preceding crop plants were cut down, had the tops harvested, or were destroyed by a nonselective herbicide (the old crop is not removed or incorporated into the soil as is common in preparing a plant bed)

Nucleic acid

genetic material of all living organisms, including dna (deoxyribonucleic acid) and rna (ribonucleic acid)


region in prokaryotes, chloroplasts, and mitochondria where the dna is concentrated. Unlike a nucleus, it is not bound by a membrane.


dense aggregation of proteinaceous matter and nucleic acid in cells, surrounded by a membrane; contains chromosomes and controls heredity


a subunit of a nucleic acid, either dna or rna

Obligate parasite (syn. Biotroph)

organism that can grow only as a parasite in association with its host plant and cannot be grown in artificial culture media


block or plug that stops flow of liquids (as in vessels)

Oedema (also edema; syn. Intumescence)

blisters produced on leaves and other plant parts under conditions of high moisture and restricted transpiration

Oligogenic resistance

resistance conferred by a few genes (see monogenic resistance, multigeneic resistance, polygenic resistance, single gene resistance)

Oogonium (pl. Oogonia)

female gametangium of oomycetes, containing one or more gametes

Oomycetes (adj. Oomycetous)

class of fungal-like organisms typically with nonseptate mycelium, asexual sporangia and zoospores, and sexual oospores


thick-walled, sexually-derived resting spore of oomycetes


mass of bacterial cells mixed with host fluids

Open reading frame

portion of a nucleic acid molecule that is translated into a protein


a membrane-bound structure within a cell having a specialized function, e.g. mitochondria and chloroplasts


describing a molecule containing carbon atoms; pertaining to living organisms

Ostiole (adj. Ostiolate)

pore; opening in the papilla or neck of a perithecium, pseudothecium, or pycnidium through which spores are released


exterior, nonliving portion of bark in woody plants


the female reproductive structure of organisms; in plants, enlarged basal portion of a pistil, containing the ovules and developing into the fruit


to survive or persist from one planting season to the next


to survive or persist through the winter period


to deposit or lay eggs with an ovipositor


enclosed structure that, after fertilization, becomes a seed; egg contained within an ovary


a secondary air pollutant that is a highly reactive form of oxygen (o3) formed when the exhaust of automobiles and other internal combustion engines is in the presence of sunlight

Ozone layer

a protective layer of ozone in the upper atmosphere that reduces ultraviolet radiation

Palisade parenchyma

tissue found beneath the upper epidermis of leaves, composed of elongate, tubular cells arranged upright in the manner of posts in a palisade fortification

Pan (abbr. For peroxyacetyl nitrates)

a secondary air pollutant formed when the exhaust of automobiles and other internal combustion engines is in the presence of sunlight


a widespread and destructive outbreak of disease simultaneously in several countries


nipple-like projection; used to describe the tip of some sporangia and the localized wall thickenings on the inner surface of plant cell walls at sites penetrated by fungi


having the antheridium contact the oogonium on the side, as in many pythium sp. (see amphigynous)


a type of recombination, found in certain heterokaryotic fungi, that is based on mitosis rather than meiosis. Genetically distinct haploid nuclei fuse in the heterokaryon. The resulting diploid nuclei multiply by mitotic division, with some crossing-over, and a diploid homokaryon develops. During repeated mitotic divisions, chromosomes may be shed by the diploid nucleus to produce a haploid nucleus.

Parasite (adj. Parasitic)

organism that lives in intimate association with another organism on which it depends for its nutrition; not necessarily a pathogen

Parenchyma (adj. Parenchymatous)

soft tissue of living plant cells with undifferentiated, thin, cellulose walls

Parthenogenesis (adj. Parthenogenetic)

reproduction by the development of an unfertilized egg

Partial resistance

resistance in which disease develops more slowly on the host or to a lesser extent, but the host does become diseased (see complete resistance)


to free a material, usually a liquid, of selected harmful microorganisms using heat

Pathogen (adj. Pathogenic)

a disease-producing organism or agent


production and development of disease

Pathogenesis-related (pr) proteins

proteins, such as antimicrobial proteins and hydrolytic enzymes, that are synthesized in the early events of the plant defense response


ability to cause disease


the study of diseases


a subdivision of a pathogen species characterized by its pattern of virulence or avirulence to a series of differential host varieties

Pathovar (abbr. Pv.)

A subdivision of a plant pathogenic bacterial species defined by host range; pathovar for bacteria is equivalent to forma specialis for fungi

Pcr (acronym for polymerase chain reaction)

a technique used to amplify the number of copies of a specific region of dna in order to produce enough of the dna for use in various applications such as identification and cloning


a methylated polymer of galacturonic acid found in the middle lamella and the primary cell wall of plants; jelly-forming substance found in fruit


small slender stalk; stalk bearing an individual flower, inflorescence, or spore


stalk or main stem of an inflorescence; part of an inflorescence, or a fructification


initial invasion of a host by a pathogen

Penetration peg (syn. Infection peg)

the specialized, narrow, hyphal strand on the underside of an appressorium that penetrates host cells


antibiotic produced by certain species of penicillium and effective against gram-positive bacteria


something that occurs year after year; plant that survives for several to many years (see annual, biennial)


sexual; capable of sexual reproduction (see teleomorph)

Perfect flower

flower possessing both stamens and pistils

Perfect state (syn. Teleomorph)

the sexual form in the life cycle of a fungus (see anamorph)


fruit wall


layer or layers of cells between the phloem and the endodermis of roots, giving rise to branch roots

Perithecium (pl. Perithecia)

flask-shaped or subglobose, thin-walled fungus fruiting body (ascocarp) containing asci and ascospores; spores are expelled or released through a pore (ostiole) at the apex


having hairs or flagella distributed over the whole surface

Peroxyacetal nitrates (pan)

a secondary air pollutant formed when the exhaust of automobiles and other internal combustion engines is in the presence of sunlight

Persistent transmission (syn. Circulative transmission)

a type of virus transmission in which the virus is acquired and transmitted by the vector after relatively long feeding times and remains transmissible for a prolonged period while in association with its vector


any organism that damages plants or plant products


a chemical used to control pests


stalk portion of a leaf (see lamina)


negative logarithm of the effective hydrogen ion concentration; a measure of acidity (ph 7 is neutral; values less than ph 7, acidic; greater than ph 7, alkaline)


cork; a protective tissue composed of nonliving cells with suberized walls produced by the phellogen and accumulating on the surface of stems and roots


tissue formed by and internal to the phellogen; resembles the cortical parenchyma in morphology


cork cambium; lateral meristem forming the periderm, a protective tissue in stems and roots; phellem (cork) is produced toward the surface, phelloderm toward the inside

Phenological synchrony

the coordinated development of parasites and their hosts based on degree-days and other environmental factors so that parasites can successfully infect their hosts, such as the production and release of ascospores of venturia inaequalis, the apple scab pathogen, from fallen leaves from the previous season, when new apple leaves are expanding.


external, visible physical characteristics of an organism determined by the interaction of its genotype with the environment (see genotype)


chemical substance that attracts members of the same species or one sex of that species, esp. Insects and nematodes


end cell of a conidiophore with one or more open ends through which a basipetal succession of conidia develops


food-conducting, food-storing tissue in the vascular system of roots, stems, and leaves

Phloem necrosis

death of phloem cells, often visible, caused by infection by systemic phloem pathogens such as phytoplasmas, spiroplasmas, and viruses


chemical reactions that require sunlight


product of photosynthesis


manufacture of carbohydrates from carbon dioxide and water in the presence of chlorophyll(s), using light energy and releasing oxygen


archaic term for a member of a group of fungi without cross walls (septa) in their mycelium


change of floral organs to leaflike structures


leaf surface


used to describe epiphytic microorganisms adapted to living on the leaf surface


arrangement of leaves on a stem in relation to one another


substance produced in higher plants in response to a number of chemical, physical, and biological stimuli that inhibits the growth of certain micro-organisms


able to cause disease in plants

Phytopathology (syn. Plant pathology)

the study of plant diseases

Phytoplasma (syn. Mycoplasmalike organism, mlo)

plant-parasitic pleomorphic mollicute (prokaryote with no cell wall) found in phloem tissue; cannot yet be grown on artificial nutrient media

Phytosanitary certificate

official document that indicates that plant material has been inspected and found to be free of certain pathogens


harmful to plants (usually used to describe chemicals)


a colored compound, such as chlorophyll, in the cells of plants or fungi


the ovule-bearing organ of the plant consisting of the ovary and its appendages (e.g. style, stigma)


parenchymatous tissue occupying the center of the stem

Plant pathology (syn. Phytopathology)

the study of plant diseases


a circular, self-replicating hereditary element that is not part of a chromosome; plasmids are used in recombinant dna experiments as acceptors and vectors of foreign dna

Plasmodesma (pl. Plasmodesmata)

cytoplasmic strands that connect living cells


a fungus-like group of organisms, sometimes called the plasmodiophoromycota or the endoparasitic slime molds, characterized by the production of zoospores and plasmodia that are restricted to the cells of their host.

Plasmodium (pl. Plasmodia)

naked multinucleate mass of protoplasm moving and feeding in amoeboid fashion


the fusion of two sex cells


shrinking of a protoplast due to water loss from the vacuole of a plant cell


able to assume various shapes (and perhaps sizes); occurrence of more than one distinct form in the life cycle of an organism


the number of (complete) sets of chromosomes in a cell, e.g. haploid, diploid, polyploid


at one end or pole of the cell


male sex cells produced by anthers of flowering plants or the cones of seed plants


transfer of pollen from anther to stigma or from a staminate cone to an ovulate cone

Polyclonal antibody

a preparation containing antibodies against more than one epitope of an antigen (see monoclonal antibody)


having several to many disease cycles in a growing season (see monocyclic)


requiring more than one year to complete one life or disease cycle


pertaining to, or governed by, many genes (see monogenic)

Polygenic resistance (syn. Multigenic resistance)

resistance conferred by several genes (see monogenic resistance, oligogenic resistance, single gene resistance)

Polymerase chain reaction (pcr)

a technique used to amplify the number of copies of a specific region of dna in order to produce enough of the dna for use in various applications uch as identification and cloning


having three or more complete sets of chromosomes (see haploid, diploid)


a protein translated from an entire viral genome which is then cleaved by proteases (protein-degrading enzymes) into the active protein products

Pome (syn. Pome fruit)

simple, fleshy, indehiscent fruit derived from several carpels, e.g. apple, pear, quince

Positive sense rna

rna that can serve directly as messenger rna (see negative sense rna)


toward the back or rear; (see anterior)

Powdery mildew

a white, powdery, superficial ascomycetous fungus that is an obligate parasite and generally is found only on one or a few closely related species of plants

Predispose (n. Predisposition)

to make prone to infection and disease

Primary inoculum (syn. Initial inoculum)

inoculum, usually from an overwintering source, that initiates disease in the field, as opposed to inoculum that spreads disease during the season

Primary leaf

first true leaf that emerges on a plant following the cotyledons

Primary pollutant

air pollutant that is released directly into the atmosphere and is harmful to plants, e.g. so2 or nox

Primary root

root that develops directly from the radicle of an embryo rather than from a crown or node


small fragment of nucleic acid with a free 3'-hydroxyl group necessary for initiation of dna, and, sometimes, rna synthesis; often specific fragments chosen for use in polymerase chain reaction (pcr) for rapid identification of pathogens


a plant defense compound that is already present before invasion by a pathogen


an organism without internal membrane-bound organelles, lacking a distinct nucleus, such as bacteria and mollicutes (see eukaryote)

Promycelium (pl. Promycelia)

in rust and smut fungi, a germ tube issuing from the teliospore and bearing the basidiospores

Propagative transmission (syn. Circulative propagative transmission)

pathogen transmission characterized by a long period of acquisition of the pathogen (usually a mollicute, e.g. phytoplasma or spiroplasma, and sometimes a virus) by a vector (typically an insect), a latent period before the vector is able to transmit the pathogen, and retention of the pathogen by the vector for a long period because the pathogen reproduces or replicates in the vector


any part of an organism capable of independent growth


agent, usually a chemical, applied to a plant surface in advance of a pathogen to prevent infection

Protectant fungicide (syn. Contact fungicide)

a fungicide that remains on the surface where it is applied; no after-infection activity (see systemic fungicide)


a principle of plant disease control in which a barrier is placed between the susceptible plant and pathogen (e.g. the use of protective chemical dusts or sprays)


a nitrogen-containing organic compound composed of units called amino acids


living contents of a cell


living cell exclusive of a wall


nearest to the point of attachment (see distal)

Pseudothecium (pl. Pseudothecia)

perithecium-like fruiting body containing asci and ascospores dispersed rather than in an organized hymenium; an ascostroma with a single locule or cavity and containing bitunicate asci

Puccinia pathway

the region through which rust urediniospores move from southern areas through all grain-producing areas of the united states to canada each season

Pupa (pl. Pupae; v. Pupate)

quiescent stage between the larva and the adult of certain insects


small blisterlike elevation of epidermis formed as spores emerge

Pv. (abbr. For pathovar)

a subdivision of a plant pathogenic bacterial species defined by host range; pathovar for bacteria is equivalent to forma specialis for fungi


spore (conidium) produced in a pycnidium

Pycnidium (pl. Pycnidia)

asexual, globose or flask-shaped fruiting body of certain imperfect fungi producing conidia

Pycniospore (syn. Spermatium)

haploid, sexually derived spore formed in a pycnium of rust fungi

Pycnium (pl. Pycnia; syn. Spermagonium)

globose or flask-shaped haploid fruiting body of rust fungi bearing receptive hyphae and pycniospores


the addition, through plant breeding or genetic engineering, of several resistance genes into a single plant cultivar

Qualitative resistance

resistance reactions that can be placed in distinct categories, usually conferred by one or a few genes. (see quantitative resistance)

Quantitative resistance

resistance reactions that have no distinct classes but vary continuously from resistant to susceptible, the result of few to many genes the individual effects of which may be small and difficult to detect. (see qualitative resistance)


legislative control of the transport of plants or plant parts to prevent the spread of pests or pathogens


dormant or inactive

Quorum sensing

the ability of bacteria to interact with each other through a variety of mechanisms; allows a population of bacteria to behave more like a multicellular organism


subgroup or biotype within a species or variety, distinguished from other races by virulence, symptom expression, or host range, but not by morphology


elongated main axis of an inflorescence


part of the plant embryo that develops into the primary root

Race non-specific resistance (syn. General resistance, horizontal resistance)

resistance which is effective against all biotypes of the pathogen. (see durable resistance, specific resistance, vertical resistance)


tissue that extends radially in the secondary xylem and phloem of a woody plant


the structure of a flower that bears the reproductive organs

Receptive hypha

the part of a rust fungus pycnium (spermogonium) that receives the nucleus of a pycniospore (spermatium)


a site that recognizes and binds an elicitor; any organ or molecular site that is sensitive to a distinct (specific) signal molecule


describes a phenotypic trait that is expressed in diploid organisms only if both parents contribute the trait to the progeny (see dominant)

Recombinant dna

dna molecules in which sequences, not normally contiguous, have been placed next to each other by in vitro methods




an enzyme involved in the replication (copying) of nucleic acid


the process by which a dna or rna molecule makes an exact copy of itself;

repetition of an experiment or procedure at the same time and place (one of several identical experiments, procedures, or samples);

the process by which a virus particle induces the host cell to reproduce the virus


sticky to brittle plant product derived from essential oils; often a defense compound of conifers


a disease symptom in which there is a copious flow of resin from a wound or infection site of a conifer

Resistant (n. Resistance)

possessing properties that prevent or impede disease development (see susceptible)


series of chemical reactions that make energy available through oxidation of carbohydrates and fat

Resting spore

spore, often thick-walled, that can remain alive in a dormant state for some time, later germinating and capable of initiating infection

Restriction endonuclease

enzyme that cleaves dna at a particular base sequence; sometimes informally referred to as a restriction enzyme


having netlike markings

Reverse transcriptase

enzyme used to make complementary dna from a piece of rna, such as a plant virus


genus of bacteria that lives symbiotically with roots of leguminous plants; during the symbiosis, atmospheric nitrogen gas is converted into a form useable by the plant

Rhizobium nodules

galls on roots caused by rhizobium spp.


macroscopic rope-like strand of compacted tissue formed by certain fungi


microenvironment in the soil, immediately around plant roots


used to describe microorganisms adapted to living in the rhizosphere of a plant

Ribonucleic acid (abbr. Rna)

several nucleic acids composed of repeating units of ribose (a sugar), a phosphate group, and a purine (adenine or guanine) or a pyrimidine (uracil or cytosine) base; transcribed from dna and involved in translation to proteins


a mostly horizontal, jointed, fleshy, often elongated, usually underground stem

Ribosomal rna (abbr. Rrna)

rna molecules forming part of the ribosomal structure


a subcellular protoplasmic particle, made up of one or more rna molecules and several proteins, involved in protein synthesis


disease symptom characterized by yellowish or necrotic rings enclosing green tissue, as in some plant diseases caused by viruses

Rna (abbr. For ribonucleic acid)

several nucleic acids composed of repeating units of ribose (a sugar), a phosphate group, and a purine (adenine or guanine) or a pyrimidine (uracil or cytosine) base; transcribed from dna and involved in translation to proteins


to remove and destroy individual plants that are diseased, infested by insects, or otherwise undesirable

Root cap

a group of cells on a root that protects the growing tip

Root exudates

the various compounds that leak from growing and expanding sections of roots as well as from broken cells at exit points of lateral roots

Root graft

the fusion of roots of two adjacent plants so that their water and food conducting (vascular) systems become joined

Root hair

threadlike, single-celled outgrowths from a root epidermal cell


portion of the stem (trunk) and associated root system into which a bud or scion is inserted in grafting; fleshy overwintering part of a herbaceous perennial plant with buds and eyes (see scion)


disease symptom characterized by short, bunchy growth habit due to shortened internodes and no comparable reduction in leaf size


softening, discoloration, and often disintegration of plant tissue as a result of fungal or bacterial infection


growth of different kinds of crops in succession in the same field



Rrna (abbr. For ribosomal rna)

rna molecules forming part of the ribosomal structure


wrinkled, roughened

Runner (syn. Stolon)

a slender horizontal stem that grows close to the soil surface

Runner plants

new plants produced asexually on a runner or stolon


brownish, roughened areas resulting from cork formation


a disease caused by a specialized group of basidiomycetes that often produces spores of a rusty color


destruction or removal of infected and infested plants or plant parts; decontamination of tools, equipment, containers, work space, hands, etc.

Sap transmission

transmission, usually of viruses, by rubbing sap from an infected plant onto a healthy plant to cause infection

Saprobe (syn. Saprophyte)

organism that obtains nourishment from non-living organic matter

Saprophyte (adj. Saprophytic; syn. Saprobe)

organism that obtains nourishment from non-living organic matter


physiologically active zone of wood contiguous to cambium (see heartwood)


roughened, crustlike diseased area on the surface of a plant organ


a necrotic condition in which tissue is usually bleached and has the appearance of having been exposed to high temperatures


portion of a shoot used for grafting onto the root stock (see rootstock)

Sclerenchyma (adj. Sclerenchymatous)

tissue made up of thick-walled plant cells

Sclerotium (pl. Sclerotia)

a vegetative resting body of a fungus, composed of a compact mass of hyphae with or without host tissue, usually with a darkened rind


any symptom that suggests the action of flame or fire on the affected part, often seen at the margins of leaves

Secondary infection

infection resulting from the spread of infectious material produced after a primary infection or from secondary infections without an intervening inactive period

Secondary inoculum

inoculum produced by infections that took place during the same growing season

Secondary metabolite

a compound produced in microbes (e.g., mycotoxins, syringomycins) or plants (e.g., caffeine or nicotine) that is not necessary for normal growth and development

Secondary organism

organism that multiplies in already diseased tissue but is not the primary pathogen

Secondary pollutant

air pollutant that must be chemically produced from other air pollutants, e.g. ozone (o3) that is a product of a photochemical reaction of exhaust products from combustion engines in the atmosphere

Secondary root

branch from a primary root


remaining in a fixed location (see migratory)


ripened ovule consisting of an embryo and stored food enclosed by a seed coat

Seed treatment

application of a biological agent, chemical substance, or physical treatment to seed, to protect the seed or plant from pathogens or to stimulate germination or plant growth


carried on or in a seed

Selective medium

a culture medium containing substances that specifically inhibit or prevent the growth of some species of microorganisms


a process in which sexual reproduction occurs as a result of the fusion of sex cells produced by the same individual (see cross-fertilization)

Senesce (adj. Senescent, n. Senescence)

to decline, as with maturation, age, or disease stress


one of the modified leaves comprising a calyx


with cross walls; having septa

Septum (pl. Septa; adj. Septate)

dividing wall; in fungi, cross wall

Serology (adj. Serologic)

a method using the specificity of the antigen-antibody reaction for the detection and identification of antigenic substances and the organisms that carry them


edges with teeth, like a saw


used in reference to a leaf, leaflet, flower, floret, fruit, ascocarp, basidiocarp, etc., without a stalk, petiole, pedicel, stipe or stem; (of nematodes) permanently attached; not capable of moving about

Seta (pl. Setae)

bristle or hair-like structure, usually deep yellow or brown and thick-walled

Severity values

a means to quantify accumulating opportunities for pathogen infection (e.g. infection periods) to a pre-determined threshold that requires a disease management activity (e.g. a fungicide application); used in disease prediction or forecasting

Sexual reproduction

reproduction involving fusion of two haploid nuclei (karyogamy) to form a diploid nucleus followed by meiosis (reduction division) back to haploid nuclei at some point in the life cycle, resulting in genetic recombination

Sexual spore

spore produced during the sexual cycle

Sexually compatible

able to be cross-mated or cross-fertile


symptom in which small lesions fall out of leaves, giving the leaf the appearance of being hit by buckshot

Sieve element (syn. Sieve tube element)

a tube-shaped living cell in the phloem functioning in the transport of dissolved organic substances in the plant


indication of disease from direct observation of a pathogen or its parts (see symptom)

Single gene resistance (syn. Monogenic resistance)

resistance conferred by a single gene

Slime molds (syn. Myxomycetes)

saprophytic organisms that form vegetative amoeboid plasmodia and spores


a disease caused by a smut fungus (ustilaginales) in the basidiomycota or the fungus itself; it is characterized by masses of dark brown or black, dusty to greasy masses of teliospores that generally accumulate in black, powdery sori

Soft rot

softening, discoloration, and often disintegration of plant tissue as a result of fungal or bacterial infection

Soil drench

application of a solution or suspension of a chemical to the soil, especially pesticides to control soilborne pathogens


carried on or beneath the soil surface

Soil inhabitant

an organism that maintains its population in soil over a period of time

Soil invader

an organism whose population in soil diminishes in several months to years

Soil pasteurization

process used to free soil of selected harmful microorganisms using heat

Soil sterilization

process used to free soil of all microorganisms


disease control practice in which soil is covered with polyethylene sheeting and exposed to sunlight, thereby heating the soil and controlling soilborne plant pathogens

Sooty mold

black, nonparasitic, superficial fungal growth on honeydew produced by aphids and other phloem-feeding insects

Sorus (pl. Sori)

compact fruiting compact fruiting structure, especially the erumpent spore mass in the rust fungi (uredinales) and smut fungi (ustilaginales); occasionally a group of fruiting bodies as in synchytriaceae; a cluster of sporangia on a fern sporophyte

Sp. (abbr. For species; pl. Spp.)

A genus name followed by sp. Means that the particular species is undetermined; spp. After a genus name means that several species are being referred to


any one kind of life subordinate to a genus but above a race; a group of closely related individuals of the same ancestry, resembling one another in certain inherited characteristics of structure and behavior and relative stability in nature; the individuals of a species ordinarily interbreed freely and maintain themselves and their characteristics in nature

Specific epithet

the second word in a latin binomial

Specific resistance (syn. Vertical resistance)

resistance which is effective against some biotypes or races of the pathogen, but not others, usually inherited monogenically and expressed qualitatively. (see general resistance, horizontal resistance, race-nonspecific resistance)

Spermagonium (pl. Spermagonia; syn. Pycnium for rust fungi)

structure in which male reproductive cells are produced; in rust fungi, globose or flask-shaped haploid fruiting body composed of receptive hyphae and spermatia (pycniospores)

Spermatium (pl. Spermatia; syn. Pycniospore for rust fungi)

a male sex cell; a nonmotile male gamete; a haploid male gamete


copulatory organ of male nematode


spike-like appendage comprised of one or more reduced flowers and associated bracts; unit of inflorescence in grasses; a small spike


spiral-shaped plant pathogenic mollicute (prokaryote without cell wall)

Spontaneous generation, theory of

the theory, now known to be invalid, that plants, animals and microorganisms arose suddenly from non-living materials under certain environmental conditions


sporangium-bearing body of a fungus


non-motile, asexual spore that is borne in a sporangium

Sporangium (pl. Sporangia)

saclike fungal structure in which the entire contents are converted into an indefinite number of asexual spores


reproductive structure of fungi and some other organisms, containing one or more cells; a bacterial cell modified to survive an adverse environment

Sporidium (pl.sporidia)

basidiospore of rust fungi, smut fungi, and other basidiomycota


spore-bearing fruiting body

Sporodochium (pl.sporodochia)

superficial, cushion-shaped asexual fruiting body consisting of a cluster of conidiophores


a spore-producing or spore-bearing structure such as a conidiophore, ascocarp or basidiocarp


the diploid stage of a plant (see gametophyte)


to produce spores


a symptom of disease characterized by a limited necrotic area, as on leaves, flowers, and stems


early part of the yearly xylem growth ring in woody plants consisting typically of cells that are larger than those formed later in the season (summerwood)

Stabilizing selection

the theorized competitive disadvantage of unnecessary virulence genes; races with excess genes would have decreased fitness relative to races with fewer virulence genes, so a "super-race" would be less likely to appear in multiline crops


defoliated, dead or dying major branches in the crown of a tree, usually resulting from inadequate water uptake or translocation

Stamen (adj. Staminal)

male structure of a flower, composed of a pollen-bearing anther and a filament, or stalk


central cylinder of vascular tissue (especially in roots)

Stem pitting

a viral disease symptom characterized by depressions on the stem

Sterigma (pl. Sterigmata)

small, usually pointed projection that supports a spore


unable to reproduce sexually;

Sterile fungus

to be free of living microorganisms

Sterilization (adj. Sterilized)

a fungus that is not known to produce any kind of spores


the total destruction of living organisms by various means, including heat, chemicals or irradiation


portion of a flower that receives pollen and on which the pollen germinates




series of small dots or speckles in which chlorophyll is absent

Stolon (syn. Runner)

small leaflike appendage at the base of a leaf petiole, usually occurring in pairs

Stoma (pl. Stomata; adj. Stomatal; also stomate)

a slender, horizontal stem that grows close to the soil surface; in fungi, a hypha that grows horizontally along the surface

Stone fruit

structure composed of two guard cells and the opening between them in the epidermis of a leaf or stem, functioning in gas exchange


fruit with a stony endocarp, e.g. cherry, peach, plum

Striate (n. Striations)

a distinct form of an organism or virus within a species, differing from other forms of the species biologically, physically, or chemically

Stroma (pl. Stromata)

marked with delicate lines, grooves, or ridges


compact mass of mycelium (with or without host tissue) that supports fruiting bodies or in which fruiting bodies are embedded


reduction in height of a vertical axis resulting from a progressive reduction in the length of successive internodes or a decrease in their number


slender part of many pistils located between the stigma and the ovary and through which the pollen tube grows

Stylet knob (syn. Basal knob)

stiff, slender, hollow feeding organ of plant-parasitic nematodes or sap-sucking insects, such as aphids or leafhoppers

Stylet-borne transmission (syn. Nonpersistent transmission)

structure at the base of a nematode stylet


a type of virus transmission in which the virus is acquired and transmitted by the vector after short feeding times, and is retained by the vector for only a short period of time

Subgenomic rna

to convert into cork tissue


a piece of viral rna, shorter than the entire genome of the virus, found in cells infected by the virus and sometimes encapsidated


a subpopulation of a species, defined on the basis of more than one character (morphologic for many organisms) that distinguishes the members of the subpopulation from other members of that species

Sulfur dioxide (so2)

the substance on which an organism lives or from which it obtains nutrients; chemical substance acted upon, often by an enzyme


a primary air pollutant produced in industrial processes and coal burning that causes interveinal necrosis on broadleaf plants and tip necrosis on conifers

Sunscald or sunburn

part of the yearly xylem growth ring in woody plants formed late in the growing season and consisting of cells smaller than those of springwood

Suppressive soil

injury of plant tissues burned or scorched by direct sun or or sunburn


soil in which various diseases are naturally at lower levels than expected due to biological factors in the soil; an example of natural biological control

Susceptible (n. Susceptibility)

an abbreviated term for a susceptible plant

Symbiosis (adj. Symbiotic; n. Symbiont)

prone to develop disease when infected by a pathogen (see resistance)


mutually beneficial association of two different kinds of organisms


pertaining to proliferation of axes, in which each successive spore or branch develops behind and to one side of the previous apex where growth has ceased

Symptomless carrier

indication of disease by reaction of the host, e.g. canker, leaf spot, wilt (see sign)

Syncytium (pl. Syncytia)

a plant that, although infected with a pathogen (usually a virus), produces no obvious symptoms

Synergism (adj. Synergistic)

a multinucleate structure in root tissue formed by dissolution of common cell walls induced by secretions of certain sedentary plant-parasitic nematodes, e.g. cyst nematodes

Synnema (pl. Synnemata; syn. Coremium)

greater than additive effect of interacting factors


compact or fused, generally upright conidiophores, with branches and spores forming a headlike cluster


the study of the kinds of organisms and the relationships between them

Systemic acquired resistance (sar)

pertaining to a disease in which the pathogen (or a single infection) spreads generally throughout the plant; pertaining to chemicals that spread internally through the plant

Systemic fungicide

reduced disease symptoms on a portion of a plant distant from the area where a hypersensitive response occurred or other stimulus was applied; a rapid and coordinated defense response against a variety of pathogens as a signal travels throughout the plant (see induced systemic resistance)


a fungicide that is absorbed into plant tissue and may offer some curative or after-infection activity; includes fungicides that are locally systemic, xylem-mobile (upward moving), and amphimobile (move in phloem upward as well as downward in the plant) (see contact or protectant fungicide)

Taxonomy (adj. Taxonomic)

primary root that grows vertically downward and from which smaller lateral roots branch

Teleomorph (syn. Perfect state)

the science dealing with naming and classifying organisms

Teliospore (sometimes called teleutospore, teleutosporodesm)

the sexual form in the life cycle of a fungus (see anamorph and holomorph)

Telium (pl. Telia)

thick-walled resting or overwintering spore produced by the rust fungi (uredinales) and smut fungi (ustilaginales) in which karyogamy occurs; it germinates to form a promycelium (basidium) in which meiosis occurs

Temporary wilt

fruiting body (sorus) of a rust fungus that produces teliospores


wilt due to insufficient soil water from which a plant can recover when water is supplied

Testa (pl.testae)

a chemical that causes malformations in the fetus


seed coat


vegetative body of a fungus


tightly intertwined layer of plant litter from accumulations of undecomposed or partially decomposed plant residues


use of heat to reduce or eliminate pathogens in plant tissue; often used on plants prior to meristem culture to produce pathogen-free plants


insect body part between the head and abdomen


the process of turning or stirring the soil


a lateral shoot, culm, or stalk arising from a crown bud; common in grasses

Tissue culture

group of cells, usually of similar structure, that perform the same or related functions


in vitro method of propagating healthy cells from plant tissues

Tolerance (adj. Tolerant)

concentration of a virus


ability of a plant to endure an infectious or noninfectious disease, adverse conditions, or chemical injury without serious damage or yield loss; (of pesticides) the amount of chemical reside legally permitted on an agricultural product entering commercial channels and usually measured in parts per million (ppm)


the concept that even specialized cells contain all of the genetic information for an organism and, therefore, any cell should be able to regenerate into any tissue or into an entire plant


capacity of a substance to interfere with the vital processes of an organism


poisonous substance of biological origin


elongated conducting cell of the xylem, with tapering or oblique end walls and pitted walls


the production of a complementary strand of rna from a segment of dna

Transfer rna (abbr. Trna)

the transfer of genes from one organism to another by viruses, especially in bacteria


the rna that moves amino acids to the ribosome to be placed in the order prescribed by the messenger rna

Transgenic (syn. Genetically modified organism; gmo)

the transfer of genetic materials from one organism to another by humans (genetic engineering); a means of genetic variation in bacteria by absorption and incorporation of dna from another bacterial cell


possessing a gene from another species; used to describe the organisms that have been the subject of genetic engineering


the assembling of amino acids into a protein using messenger rna, ribosomes and transfer rna


movement of water, nutrients, chemicals, or food materials within a plant

Transmit (n. Transmission)

so clear that light may pass through


to spread or transfer, as in spreading an infectious pathogen from plant to plant or from one plant generation to another

Trap crop

water loss by evaporation from leaf surfaces and through stomata


crop planted around a field to protect the inner crop from diseases transmitted by aerial vectors; host crop of a parasitic plant, such as witchweed (striga spp.), that is planted to stimulate seed germination, and later sacrified by plowing under before the parasitic plant produces new seeds


physical separation of soil in a vertical plane to sever grafted roots between trees


a female receptive hypha

Triplet codon

a plant epidermal hair, of which several types exist

Trna (abbr. For transfer rna)

a set of three nucleotide bases in dna or rna that code for an amino acid


the rna that moves amino acids to the ribosome to be placed in the order prescribed by the messenger rna


an underground stem adapted for storage, typically produced at the end of a stolon

Tumor (syn. Gall)

state of being rigid or swollen as a result of internal water pressure

Tylosis (pl. Tyloses)

abnormal swelling or localized outgrowth, often roughly spherical, produced by a plant as a result of attack by a fungus, bacterium, nematode, insect or other organism


balloonlike extrusions of parenchyma cells into lumina of contiguous vessels that partially or completely block them


the example on which the description of a scientific name is based, and which fixes the application of the name (the type genus of a family, or the type species of a genus)


submicroscopic structure of a macromolecule, cell, or tissue


one-celled (see multicellular)


having one flagellum


having a single ascus wall (see bitunicate)

Urediniospore (also urediospore, uredospore)

having one nucleus (see multinucleate)

Uredinium (also uredium; pl. Uredinia)

the asexual, dikaryotic, often rusty-colored spore of a rust fungus, produced in a structure called a uredinium; the "repeating stage" of a heteroecious rust fungus, i.e. capable of infecting the host plant on which it is produced


fruiting body (sorus) of rust fungi that produces urediniospores


generally spherical organelle within a plant cell bound by a membrane and containing dissolved materials such as metabolic precursors, storage materials, or waste products

Variety (syn. Cultivar; adj. Varietal)

pattern of two or more colors in a plant part, as in a green and white leaf


a plant type within a species, resulting from deliberate manipulation, which has recognizable characteristics (color, shape of flowers, fruits, seeds, height and form)

Vascular bundle

pertaining to fluid-conducting (xylem and phloem) tissues in plants

Vascular cylinder (syn. Stele)

strand of conductive tissue, usually composed of xylem and phloem (in leaves, small bundles are called veins)

Vascular wilt disease

the cylinder of vascular tissue in stems or roots


a xylem disease that disrupts normal uptake of water and minerals, resulting in wilting and yellowing of foliage

a living organism (e.g., insect, mite, bird, higher animal, nematode, parasitic plant, human) able to carry and transmit a pathogen and disseminate disease;

(in genetic engineering) a vector or cloning vehicle is a self-replicating dna molecule, such as a plasmid or virus, used to introduce a fragment of foreign dna into a host cell


referring to somatic or asexual parts of a plant, which are not involved in sexual reproduction

Vegetative propagation

asexual reproduction; in plants, the use of cuttings, bulbs, tubers, and other vegetative plant parts to grow new plants


small vascular bundle in a leaf

Vein banding

symptom of virus disease in which regions along veins are either darker green or distinctly more yellow than tissue between veins

Vein clearing

disappearance of green color in or around leaf veins



Vertical resistance (syn. Specific resistance)

resistance which is effective against some biotypes or races of the pathogen, but not others, usually inherited monogenically and expressed qualitatively (see general resistance, horizontal resistance, race non-specific resistance)

Vertifolia effect

a term used to describe the loss of general (horizontal, minor gene, multigenic, polygenic) resistance in a cultivar after several generations of selection during which a major gene confers resistance to the dominant race or biotype of the pathogen; first observed in the potato cultivar vertifolia with late blight resistance


thin sac in which zoospores are differentiated and released;

the bulbous head terminating the conidiophores of aspergillus;

structure formed by endomycorrhizal fungi within living cells of the root


water-conducting structure of xylem tissue with pit openings in end walls

Viable (n. Viability)

the state of being alive; able to germinate, as seeds, fungus spores, sclerotia, etc.; capable of growth


state or condition in which normally white or colored tissues (e.g. flower petals) become green


complete virus particle


an infectious, nonencapsidated (naked) circular, single-stranded rna


cellular inclusions that are sites of synthesis of viral components and the assembly of virus particles


degree or measure of pathogenicity; relative capacity to cause disease


highly pathogenic; having the capacity to cause severe disease (see avirulent)


virus-laden, usually applied to insects or nematodes as vectors


a submicroscopic,intracellular, obligate parasite consisting of a core of infectious nucleic acid (either rna or dna) usually surrounded by a protein coat


sticky substance produced on the seed coat of parasitic flowering plants in the viscaceae (mistletoes) that helps attach the seed to the host plant branch


self-set plant; plant seeded by chance


exterior opening of a mature female nematode's reproductive system


separation of diseased from healthy tissues by barrier tissues produced by a diseased plant


describing disease symptom of plants or lesions that appear wet, dark, and usually sunken and translucent

Water sprout

small, rapidly growing shoot or branch on a large stem, developed from adventitious tissues

White rot (of wood)

type of wood decay resulting from enzymatic action of fungi; it degrades all components of wood, including lignin, leaving the wood light-colored and spongy

White rust

common name usually used for diseases caused by oomycetes in the genus albugo


circular arrangement of like parts

Wild type

the phenotype characteristic of the majority of individuals of a species under natural conditions


drooping of leaves and stems from lack of water (inadequate water supply or excessive transpiration);

Back to Top