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E
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 or disease level at or above which the value of crop losses (in the absence of management efforts) would exceed the cost of management practices
ecosystem
a community of living things and their environment
ectomycorrhiza (pl. ectomycorrhizae)
a symbiotic association between a nonpathogenic or weakly pathogenic fungus and the roots of plants with fungal hyphae between and external to root cells (contrasts with arbuscular mycorrhiza, endomycorrhiza)
ectoparasite
a parasite that feeds from the exterior of its host (contrasts with endoparasite)
ectotrophic
fungal development primarily over the root surface
edema
a swelling or blistering on leaves and other plant parts under conditions of high moisture and restricted transpiration (see also intumescence, oedema)
effector
a pathogen molecule, usually a protein, that is translocated into host cells where it may act to directly manipulate host innate immunity
egg mass
a group of eggs held together by a gelatinous matrix
electron microscope
a 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
the growth of the seedling shoot through the surface of the soil
enation
an 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
the inner layer of a fruit wall
endoconidium (pl. endoconidia)
a conidium produced inside a hypha or conidiophore
endodermis
the layer of cells within the root, between the vascular tissue and the cortex
endogenous
arising from the inside (contrasts with exogenous)
endomycorrhiza (pl. endomycorrhizae)
a 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 also arbuscular mycorrhiza) (contrasts with ectomycorrhiza)
endoparasite
a parasitic organism that lives and feeds from inside its host (contrasts with ectoparasite)
endophyte
a plant developing inside another organism; also used for endoparasitic fungi found in grass species
endoplasmic reticulum
the system of interconnected cytoplasmic membranes that transports materials within the cell
endosperm
the nutritive tissue formed within the embryo sac of seed plants
endospore
a resistant, thick-walled asexual spore formed within a bacterial or fungal cell
Environmental Protection Agency (acronym EPA)
the U.S. federal agency responsible for controlling the various aspects of air, water, and soil pollution, including pesticide regulations
enzyme
a 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 U.S. federal agency responsible for controlling the various aspects of air, water, and soil pollution, including pesticide regulations
epicotyl
the portion of the stem of a plant embryo or seedling above the node where the cotyledons are attached (contrasts with hypocotyl)
epidemic
an increase of disease in a population; a general and serious outbreak of disease (see also epiphytotic)
epidemiology (adj. epidemiologic)
the study of factors influencing the initiation, development, and spread of infectious disease; the study of disease in populations
epidermis (adj. epidermal)
the surface layer of cells of leaves and other plant parts
epinasty
an 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 (see also epidemic)
epiphyllous
on the upper surface of a leaf
epiphyte
an 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 (acronym for extracellular polysaccharide)
a sugar polymer that aids in movement, helps prevent desiccation, and contributes to the slimy appearance of bacteria, fungi, and nematodes; and probably promotes colonization of plant tissues and disease development in bacteria
eradication
the management 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.; a sclerotium, or resting structure, produced by Claviceps spp. and other closely related fungi in infected flowers of parasitized grain plants
ergotism
a disease of humans and other animals 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
erumpent
bursting or erupting through the substrate surface
escape
the failure of inherently susceptible plants to become diseased, even though disease is prevalent
ethylene
a plant growth regulator (hormone) influencing various aspects of vegetative growth, fruit ripening, abscission of plant parts, and the senescence of flowers
etiolation
the elongation of stems caused by reduced light intensities
etiology
the study of the causes of diseases
eukaryote
an organism containing a membrane-bound nucleus and other organelles, i.e., all higher plants, animals, fungi, and protists (contrasts with prokaryote)
exclusion
the management of disease by excluding the pathogen or infected plant material from crop production areas (e.g., by quarantines and embargoes)
exogenous
originating from the outside (contrasts with endogenous)
extracellular
outside a cell
(acronym EPS)
a sugar polymer that aids in movement, helps prevent desiccation, and contributes to the slimy appearance of bacteria, fungi, and nematodes; and probably promotes colonization of plant tissues and disease development in bacteria
extrachromosomal inheritance
the inheritance of genes not located in the nucleus, i.e., those in mitochondria and chloroplasts (see also cytoplasmic inheritance, maternal inheritance)
exudate
a liquid excreted or discharged from diseased tissues, from roots and leaves, or by fungi
F
f. sp. (abbr. for forma specialis)
a taxonomic group within a pathogenic fungal species defined in terms of host range, i.e., members of different formae speciales infect different groups of plants; forma specialis for fungi is equivalent to pathovar for bacteria
facultative
capable of changing life-style, e.g. from saprophytic to parasitic or the reverse
facultative parasite
an organism that is normally saprophytic but is capable of being parasitic
facultative saprophyte
an organism that is normally parasitic but is capable of being saprophytic
fallow
cultivated land kept free from a crop or weeds during the normal growing season
fasciation
the malformation in shoots or floral organs manifested as enlargements and flattening as if several parts were fused
fascicle (adj. fasciculate)
a small group, bundle, or cluster
fastidious
in reference to prokaryotic organisms, having special growth and nutritional requirements
FDA (acronym for the Food and Drug Administration)
the U.S. federal agency responsible for the safety regulation of cosmetics, drugs, foods, and vaccines
Federal Food, Drug, and Cosmetic Act (acronym FFDCA)
the U.S. federal law which sets legal tolerances of pesticides on food products at harvest
Federal Insecticide, Fungicide, and Rodenticide Act (acronym FIFRA)
the U.S. federal law which legislates the conditions for use of pesticides
feeder root
a fine root that absorbs water and dissolved nutrients
fermentation
the oxidation of certain organic substances in the absence of molecular oxygen
FFDCA (acronym for Federal Food, Drug, and Cosmetic Act)
the U.S. federal law which sets legal tolerances of pesticides on food products at harvest
fiber
an elongated plant cell with thick walls (in xylem and phloem), which is dead at maturity
FIFRA (acronym for Federal Insecticide, Fungicide, and Rodenticide Act)
the U.S. federal law which legislates the conditions for use of pesticides
filamentous
threadlike; filiform
fission
cell division in prokaryotes
fitness
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
an 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
a minute, discolored spot in green tissue
flexuous
having turns or windings; capable of bending
flower break
a break or stripe in flower color (see also breaking)
focus (pl. foci)
a small area of diseased plants within a population
foliar
pertaining to leaves
Food and Drug Administration (acronym FDA)
the U.S. federal agency responsible for the safety regulation of cosmetics, drugs, foods, and vaccines
Food Quality Protection Act (acronym FQPA)
the U.S. federal law which sets a health-based standard governing pesticide tolerance levels in food
forest decline
the 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 fungal species defined in terms of host range, i.e., members of different formae speciales infect different groups of plants; forma specialis for fungi is equivalent to pathovar for bacteria
fossil water
the water in aquifers that has accumulated over long periods of time and is not quickly replaced through infiltration from recent rainfall
FQPA (acronym for Food Quality Protection Act)
the U.S. 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
a general term for a spore-bearing organ of a fungus
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
an archaic term for a group of fungi without a sexual stage; also, the asexual stage of members of Ascomycota (the ascomycetes) and Basidiomycota (the basidiomycetes) (see also deuteromycetes, imperfect fungi)
fungicide (adj. fungicidal)
a chemical or physical agent that kills or inhibits the growth of fungi
fungistasis
the 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
fungistat (adj. fungistatic)
a chemical or physical agent that inhibits fungal growth, sporulation, or spore geminiation, but does not cause death
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
fusiform
spindle-shaped; tapering at each end
G
gall
an 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 (see also knot, tumor)
gallery
an insect tunnel in bark and wood
gametangium (pl. gametangia)
a cell containing gametes or nuclei that act as gametes
gamete
a sex cell
gametophyte
the haploid stage of a plant (contrasts with sporophyte)
gene
a unit within an organism controlling heritable characteristics; genes are organized on chromosomes
gene gun
a device used to bombard plant cells with metal particles coated with foreign genes to accomplish genetic engineering (see also biolistic transformation)
gene silencing
the switching off of a gene by a process other than genetic modification; one example is the disabling of a gene by small interfering RNAs (siRNAs) that target messenger RNA for destruction
gene-for-gene hypothesis
the hypothesis that corresponding genes for resistance and virulence exist in the host and pathogen, respectively
general resistance
a resistance that is effective against all biotypes of the pathogen (see also durable resistance, horizontal resistance, race-nonspecific resistance) (contrasts with 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 (acronym GMO)
an organism whose gentic makeup has been altered using genetic engineering techniques (see also transgenic)
genetics
the study of heredity and variation in organisms
genome
the complete genetic information of an organism or virus
genotype
the 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
a 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
a hypha resulting from an outgrowth of the spore wall and cytoplasm after germination
germinate (n. germination)
to begin growth (as of a seed, spore, sclerotium, or other reproductive body)
germplasm
the bearer of heredity material, often loosely applied to cultivars and breeding lines
giant cell
an enlarged, multinucleate cell formed in roots by repeated nuclear division without cell division induced by secretions of certain sedentary plant-parasitic nematodes
gibberellin
a plant growth regulator (hormone) that affects stem elongation
gill
a 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
GMO (acronym for genetically-modified organism)
an organism whose genetic makeup has been altered using genetic engineering techniques (see also transgenic)
gonad
the sexual structure in animals that produces gametes
graft
the 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
the 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
the bacteria staining red or pink in the Gram staining procedure after treatment with Gram's stain
Gram-positive
the bacteria staining violet or purple in the Gram staining procedure after treatment with Gram's stain
Gram stain
a 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
greenhouse effect
the heating of the atmosphere as radiation from the sun is converted to infrared radiation but is trapped by so-called greenhouse gases (i.e., water vapor, CO2, methane, ozone), preventing its release; this is similar to a greenhouse, in which glass traps air heated by infrared radiation
groundwater
the water contained in aquifers in the soil, sometimes in underground rivers but more often in small accumulations mixed with sand
growth regulator
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 (see also hormone)
guard cells
the paired, specialized, epidermal cells that contain chloroplasts and surround a stoma
gum
a gelatinous, sugary aggregate that is synthesized and exuded by plant tissues
gummosis (pl. gummoses)
a pathologic condition characterized by excessive formation of gums; the products of cell degeneration
guttation
the exudation of watery, sticky liquid from hydathodes, especially along leaf margins
H
habitat
a place with a particular kind of environment suitable for the growth of an organism
haploid
having a single complete set of chromosomes (1N chromosomes) (contrasts with dikaryotic, diploid, polyploid)
hardiness
the ability to withstand stress
haulm
the stems or stalks collectively
haustorium (pl. haustoria)
a 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
the central cylinder of nonfunctional xylem in a woody stem (contrasts with sapwood)
hemiparasite
a 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.) (contrasts with holoparasite)
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 (contrasts with autoecious)
heterokaryon (adj. heterokaryotic)
a cell with genetically different nuclei
heterosis
the increased vigor of hybrid offspring when compared to either parent (see also hybrid vigor)
heterothallism (adj. heterothallic)
the condition in which sexual reproduction can occur only in the presence of genetically different mycelia (contrasts with homothallism)
heterotroph
an organism that obtains nourishment from outside sources and must obtain its carbon from organic carbon compounds (contrasts with autotroph)
heterozygous
having alternate forms (allele) of a gene on homologous chromosomes (contrasts with homozygous)
holomorph
the whole fungus in all its states (contrasts with anamorph, imperfect state, perfect state, teleomorph)
holoparasite
a 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.) (contrasts with hemiparasite)
homothallism (adj. homothallic)
a condition in which sexual reproduction occurs with a single thallus; self-fertile (contrasts with heterothallism)
homozygous
having the same form (allele) of a gene on homologous chromosomes (contrasts with heterozygous)
honeydew
the sugary ooze or exudate, often from aphids, and a characteristic symptom of ergot
horizontal resistance
a resistance which is effective against all biotypes of the pathogen (see also durable resistance, general resistance, race-nonspecific resistance) (contrasts with specific resistance, vertical resistance)
hormone
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, auxin, cytokinin, and gibberellin (see also growth regulator)
host plant
a 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
HR (acronym for hypersensitive response)
the rapid and localized cell death at the site of infection in resistant interactions between plants and pathogens
hyaline
transparent or nearly so; translucent; often used in the sense of colorless
hybrid (v. hybridize)
the offspring of two individuals of different genotypes
hybrid vigor
the increased vigor of hybrid offspring when compared to either parent (see also heterosis)
hybridoma
a cell produced by the fusion of an antibody-producing cell and a lymphoma (cancer) cell for production of monoclonal antibodies
hydathode
an epidermal leaf structure specialized for secretion or exudation of water; leaf opening at terminus of vein
hydrogen fluoride (HF)
a primary pollutant from volcanoes and several industrial processes such as brick factories, aluminum smelters, and phosphate fertilizer factories.
hydrological cycle
the cycling of water molecules among gaseous form (water vapor), liquid, and ice
hymenium
a continuous, spore-bearing layer of a fungus fruiting body
hyperparasite
an organism that is parasitic upon another parasite
hyperplasia (adj. hyperplastic)
the 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
a 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 (acronym HR)
the rapid and localized cell death at the site of infection in resistant interactions between plants and pathogens
hypertrophy (adj. hypertrophic)
the 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)
a single, tubular filament of a fungal thallus or mycelium; the basic structural unit of a fungus
hyphal sheath
a dense hyphal mass of ectomycorrhizal fungus enclosing the short feeder roots of plants (see also mantle)
hyphomycetes
an archaic term for the deuteromycetes (Fungi imperfecti, the imperfect fungi) that produce conidia freely or on a sporodochium or synnema (contrasts with coelomycetes)
hyphopodium
a 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
the portion of the stem below the cotyledons and above the root (see epicotyl)
hypovirulence
the reduced ability to cause disease
