General Glossary

Absorption

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+™ active

This is the name of the active ingredient in the It’s Fresh! filters. It is made from a proprietary blend of clay and minerals.</p><p>The combination of the porous nature of the clay and the formulation of the minerals means e+™ 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

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.</p><p>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

It’s 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”.</p><p>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.</p><p>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.

Freshasphere™

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.</p><p>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.</p><p>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.</p><p>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.

It’s Fresh! berry pad

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

It’s 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.

It’s Fresh! Label

The It’s Fresh! label provides an automated, integrated packaging solution with the unique It’s 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.

It’s 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 food’s 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 ‘aging hormone’ 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

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 ‘best before’, mandatory ‘use by’, 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

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.</p><p>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

Abaxial

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

Abiotic

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

Abscise

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

Abscission

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

Acid

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

Acropetal

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)

Actinomycete

a group of microorganisms similar to bacteria that produce long filaments

Acute

pertaining to symptoms that develop suddenly(see chronic)

Acute toxicity

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

Adaxial

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

Adventitious

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

Aeciospore

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

Aerial

occurring in the air

Aerification

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

Aerobic

living only in the presence of oxygen

Aflatoxin

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

Agar

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

Aggressiveness

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

Alate

winged (see apterous)

Albino (n. Albinism)

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

Alkaline

having basic (nonacidic) properties; ph greater than 7

Alkaloids

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

Allele

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

Amphid

a chemosensory organ located in the anterior region of a nematode

Amphigynous

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

Amphimixis

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

Amphimobile

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

Anaerobic

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

Annual

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

Annulations

grooved bands in the cuticle of some nematodes

Antagonism

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)

Antagonist

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

Anterior

toward the front or head (see posterior)

Anther

pollen-bearing portion of a flower

Antheridium (pl. Antheridia)

male sexual organ (male gametangium) found in some fungi

Anthesis

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

Anthracnose

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

Antibiosis

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

Antibiotic

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

Antibody

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

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

Aphid

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

Apterous

wingless (see alate)

Arable

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

Arthropod

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

Ascogenous

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

Ascospore

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

Aseptate

having no cross walls; lacking septa; nonseptate; coenocytic

Asexual

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

Autoecious

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

Autotroph

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

Auxin

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)

Avoidance

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

Awn

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

Axenic

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

Axil

the angle formed by the leaf petiole and the stem

Axillary

pertaining to or placed within an axil

Axillary bud (syn. Lateral bud)

bud that develops in the axil of a leaf

Bacilliform

shaped like short rods with rounded ends

Backcross

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

Bactericide

a chemical or physical agent that kills bacteria

Bacteriocin

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

Bacteriophage

a virus that infects a bacterium

Bacterium (pl. Bacteria)

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

Bark

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

Base

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

Basidiospore

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.

Basipetal

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)

Beetle

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

Bicellular

two-celled

Biennial

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

Biflagellate

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

Binucleate

having two nuclei

Bioassay

any test (assay) using a living organism

Biocide

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

Biotechnology

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

Biotic

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)

Biotype

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

Bitunicate

having a double ascus wall (see unitunicate)

Blasting

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

Bleeding

sap flow from a wound

Blight

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

Blotch

necrotic area of tissue irregular in form

Borer

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

Bract

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

Breaking

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

Brooming

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

Bud

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

Budding

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

Bug

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

Bulb

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

Bursa

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

Bush-type

plant with determinate growth

Callose

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

Callus

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

Calyx

outermost flower whorl; sepals, collectively

Canker

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

Canopy

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

Capsule

gel-like material surrounding a bacterial cell

Carbohydrate

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

Carcinogen

a substance or agent that causes cancer

Carpel

the ovule-bearing structure of a flower in angiosperms

Casting

premature loss of abscised leaves or twigs

Catkin

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

Cellulose

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

Center of origin

geographical area where a plant originated

Centromere

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

Certification

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

Chemotherapy

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

Chitin

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

Chlamydospore

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

Chloroplast

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

Chromosome

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

Chronic

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)

Chytridiomycetes

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)

club-shaped

Cleistothecium (pl. Cleistothecia)

a spherical ascocarp that is closed at maturity

Clone

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

Coalesce

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

Codon

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)

Coelomycetes

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

Coenocytic

having multiple nuclei embedded in cytoplasm without cross walls; nonseptate

Collar

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

Collenchyma

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

Colonization

establishment and ramification of a pathogen within a host plant

Colonize

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

Colony

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

Compartmentalization

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)

Compost

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

Concentric

one circle within another with a common center

Conidiogenesis

the formation of asexual spores (conidia)

Conidiogenous

producing and bearing conidia

Conidioma (pl. Conidiomata)

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

Conidiophore

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

Conjugation

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

Conk

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

Constitutive

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

Coppice

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

Cork

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

Corolla

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

Cotyledon

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

Cross-fertilization

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

Cross-pollination

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

Cross-protection

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

Crown

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

Crozier

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

Culm

stem of grasses, cereals and bamboos

Curl

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

Culture

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)

Cyst

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

Cytokinins

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

Cytopathology

the study of changes induced by disease at the cellular level

Cytoplasm

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

Damping-off

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

Decay

the gradual decomposition of organic matter

Deciduous

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

Defoliation

loss of leaves from a plant, whether normal or premature

Degree-day

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.

Dehiscent

opening by breaking into parts

Demicyclic

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

Dentate

toothed

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

Desiccate

to dry out

Determinate

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

Diapause

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

Dichotomous

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

Differentiation

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

Digitate

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

Dimorphic

having two distinct shapes or forms

Dioecious

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

Diploid

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)

Discomycetes

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

Disease

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

Disinfect

to eliminate a pathogen from infected plant tissues

Disinfest

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

Distal

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

Dodder

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

Dominant

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

Drought

insufficient soil water for normal plant growth

Durable resistance

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

Dwarfing

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

Echinulate

having small spines projecting from cell walls

Ecology

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

Ecosystem

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)

Ectoparasite

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

Ectotrophic

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

Elicitor

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

Embryo

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

Emergence

growth of the seedling shoot through the surface of the soil

Enation

abnormal outgrowth from the surface of a stem or leaf

Encapsidate

to cover virus nucleic acid with a protein coat

Encyst

to form a cyst or protective covering

Endemic

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

Endocarp

inner layer of a fruit wall

Endoconidium (pl. Endoconidia)

a conidium produced inside a hypha or conidiophore

Endodermis

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

Endogenous

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)

Endoparasite

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

Endophyte

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

Endosperm

nutritive tissue formed within the embryo sac of seed plants

Endospore

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

Enzyme

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

Epicotyl

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

Epidemic

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

Epinasty

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

Epiphytic

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

Epiphytotic

an epidemic in a plant population

Epiphyllous

on the upper surface of a leaf

Epiphyte

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

Epitope

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

Eradication

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

Ergot

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

Ergotism

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

Erumpent

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

Escape

bursting or erupting through the substrate surface

Ethylene

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

Etiolation

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

Etiology

elongation of stems caused by reduced light intensities

Eukaryote

the study of the causes of diseases

Exclusion

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

Exogenous

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

Extracellular

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

Exudate

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

Facultative

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

Fallow

organism that is normally parasitic but is capable of being saprophytic

Fasciation

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

Fastidious

small group, bundle, or cluster

Feeder root

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

Fermentation

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

Fiber

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

Fission

threadlike

Fitness

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

Flaccid

wilted, lacking turgor

Flag

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

Fleck

minute, discolored spot in green tissue

Flexuous

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

Foliar

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

Fructification

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

Fungistasis

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

Fusiform

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

Gallery

insect tunnel in bark and wood

Gametangium (pl. Gametangia)

cell containing gametes or nuclei that act as gametes

Gamete

sex cell

Gametophyte

the haploid stage of a plant (see sporophyte)

Gene

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)

Genetic

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

Genome

the complete genetic information of an organism or virus

Genotype

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

Geocarp

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)

Germplasm

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

Gibberellins

plant hormones (growth regulators) that affect stem elongation

Gill

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

Girdle

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

Glabrous

smooth; without hairs

Glucoside

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

Gonad

sexual structure in animals that produces gametes

Graft

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

Gram-negative

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

Gram-positive

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

Gravid

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

Gum

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

Guttation

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

Habitat

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

Haploid

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

Hardiness

ability to withstand stress

Haulm

stem or stalks collectively

Haustorium (pl. Haustoria)

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

Head

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

Heartwood

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

Hemiparasite

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.)

Herbaceous

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

Herbicide

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

Heritability

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

Heteroecious

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)

Heterotroph

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

Heterozygous

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

Holomorph

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

Holoparasite

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)

Homozygous

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

Honeydew

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

Hyaline

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

Hybridoma

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

Hydathode

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.

Hymenium

continuous, spore-bearing layer of a fungus fruiting body

Hyperparasite

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

Hypersensitive

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

Hyphomycetes

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

Hyphopodium

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)

Hypocotyl

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

Hypovirulence

reduced ability to cause disease

Icosahedral (n. Icosahedron)

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

Immune

cannot be infected by a given pathogen

Immunoassay

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

Immunosupressant

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

Indehiscent

pertaining to fruit that does not split open at maturity

Indeterminate

continuing to grow vegetatively while producing flowers or reproductive structures

Indexing

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

Induced

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)

Infect

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

Infectious

pertaining to disease, capable of spreading from plant to plant

Infective

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

Inflorescence

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

Injury

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

Insect

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

Instar

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

Intercellular

between or among cells

Intercrop

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.

Interveinal

between (leaf) veins

Intracellular

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

Isolate

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

Isometric

(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

Juvenile

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

Karyogamy

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

Knot

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

Lamina

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

Latent

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

Leafhopper

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

Leaflet

mobile insects with sucking mouthparts (order homoptera)

Leafroll

one of the separate blades or divisions of a compound leaf

Legume

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;

Lenticel

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

Lesion

localized diseased area or wound

Life cycle

the cyclical stages in the growth and development of an organism

Lignification

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

Lignin

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

Lodge

to fall over

Lumen (pl. Lumina)

central cavity of a cell or other structure

Macerate

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)

Macrocyclic

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

Macronutrient

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

Meiosis

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)

Melanin

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