the lower surface or underside of a leaf (compare adaxial)
absence of life, a disease not caused by living organisms
shedding of leaves or other plant parts (due to disease or other stress) caused by the production of a specialized layer of cells (the abscission layer) that develops at the base of the structureerumpent structure on host tissue that contains conidiophores, conidia, and sometimes setae
acid:
having a pH of less than 7
the upper surface of a leaf (compare abaxial)
dikaryotic spore of a rust fungus produced in an aecium; in heteroecious rusts, the spore stage that infects the alternate host
aecium: (pl. aecia; adj. aecial):
the fruiting body of a rust fungus in which the first dikaryotic spores (aeciospores) are produced
occurring in the air
the act of infusing or forcing air into, for example, soil
living only in the presence of oxygen
a mycotoxin; a chemical byproduct (secondary metabolite) produced by the fungi Aspergillus flavus and A. parasiticus, especially in corn and peanuts, that are harmful to humans and other animalsagar:
a jellylike material (complex polysaccharide) derived from algae and used to solidify liquid culture media; term also applied to the medium itselfaggressiveness (general virulence):
level of disease caused by an isolate of the pathogen on a given host species or variety; (no specific interactions between isolates of the pathogen and genotypes of the host are observed)an agricultural ecosystem; characterized by uniform, pioneer vegetation with very little diversity, which leads to potential instability; in general, stability in agro-ecosystems is ‘bought' by energy inputs.one form of a gene; a gene may have many alleles (forms)
allelopathy: (adj. allelopathic):
ability of one species to inhibit or prevent the growth of another species through the production of toxic substance(s)one of two different plants that a parasitic fungus (e.g. rust) must infect to complete its life cycle
a plant other than the main host that a parasite can colonize; not required for completion of life cycle of the parasite
refers to type of fertilization in which the oogonium grows through the antheridium; present in many Phytophthora species (compare paragynous)reproduction by a sexual process, (used primarily with nematodes)
living in the absence of oxygen
anamorph: (adj. anamorphic; syn. imperfect state):
the asexual form in the life cycle of a fungus, when only asexual spores (such as conidia) or no spores are producedanastomosis: (pl. anastomoses):
fusion between two hyphae or a spore and hyphae; occurs only with closely related organisms
an organism or substance that limits the action of an organism
antheridium: (pl. antheridia):
male sexual organ found in some fungi
disease caused by acervuli-forming fungi that are characterized by sunken lesions and necrosis
a chemical compound produced by one microorganism that inhibits or kills other living organisms
cup- or saucerlike ascocarp that produces asci, usually supported on a stalk
appressorium: (pl. appressoria):
swollen, flattened portion of a hyphae or germ tube that adheres to the surface of a plant, and that gives rise to infection hyphae or penetration peg
Of vesicular-arbuscular mycorrhizae: a much-branched, microscopic haustorial structure of the fungal symbiont that forms within living cortical cells of the root. The interface of the arbuscule with the plant protoplast is a site of exchange of nutrients and growth-regulating chemicals.
sexual fruiting body of the Ascomycete fungi that produces asci and ascospores; types include: apothecium, cleistothecium, perithecium, pseudothecium
a group of fungi, also called the Ascomycotina, that produces sexual spores (ascospores) within a saclike structure called an ascus
sexual spore of Ascomycetes; spore produced in an ascus
saclike structure that contains ascospores (typically eight) and usually borne in an ascocarp
having no cross walls (septa); nonseptate; coenocytic
the imperfect or anamorphic stage of a fungus; without sexual spores;
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
rust fungus that produces all spore types on one host plant (compare heteroecious)
an organism that synthesizes its own food from inorganic molecules; e.g. plants via photosynthesis (compare heterotroph)
plant hormone (growth regulator) that influences growth through cell elongation
avirulent: (syn. nonpathogenic):
organism unable to cause disease on a specific host genotype or variety (compare aggressive and virulent)
lack of disease on a potentially susceptible host that results from the decreased frequency of contact between inoculum and infection court.
a chemical or physical agent that kills bacteria
a protein antibiotic that is produced and excreted by certain strains of bacteria and that are toxic to closely related strains of the bacterium
a virus that infects a bacterium
a prokaryotic, microscopic, single-celled organism with a cell wall that multiplies by binary fission (spliting into two cells)
base:
having a pH greater than 7
sexual fruiting body of a Basidiomycete (eg. mushroom)
a group of fungi, also called the Basidiomycotina, characterized by the formation of basidiospores on basidia
haploid (1N) sexual spore produced on a basidium
a club-shaped structure on which haploid basidiospores are produced
downward from the apex toward the base of a shoot;
having two flagella
a type of asexual reproduction in which two cells, usually of similar size and shape, are formed by ivision of one cell
the scientific name of an organism, composed of two names, the first designating the genus and second the specific epithet, together referred to as the species name
having two nuclei
a test or assay that uses a living organism to detect something
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 through the use of competition, parasitism or antagonism between the organisms
the development of genetically modified organisms through the use of modern technology and processes that includes genetic engineering
living or life; diseases caused by living organisms
an organism that can live and multiply only on living cells (compare necrotroph and saprotroph); sometimes used as a synonym of obligate parasite
sudden, severe, and extensive spotting, discoloration, wilting, or destruction of leaves, flowers, stems, or entire plants
plant genotype used in a plant breeding program because it contains one or more desirable agronomic or breeding characteristics (eg. disease resistance)
application by spreading or scattering on the soil surface
an amorphous, hardened carbohydrate constituent of plant cell walls that commonly develops upon injury or infection
specialized tissues that form over a wound or cut in a plant; (compare wound healing)
a disease symptom on woody stems or trunks. Resembles an open break or wound and often persists from year to year.
the expanded leafy top of a plant or plants
the protective layer of protein (coat protein) that surrounds the nucleic acid core of a virus
a substance or agent that causes cancer
organism or agent that causes a disease or injury
structure that surrounds a cell and helps control the movement of substances into and out of the cell
protective but permeable structure secreted external to the cell membrane in plants, bacteria, fungi, and certain other organisms
carbohydrate polysaccharide composed of glucose units; major component of plant primary cell wall
geographical area where a plant or pathogen originated
complex polysaccharide in fungal cell walls, animal xoskeletons, and nematode egg shells
thick-walled or double-walled asexual resting spore formed from hyphal cells (terminal or intercalary) or by transformation of conidial cells that can function as an overwintering stage
one of a group of green pigments found in chloroplasts and important in photosynthesis
disklike structure containing chlorophyll in which photosynthesis occurs
yellowing brought about by failure of chlorophyll development caused by a disease or a nutritional disturbance
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
slow-developing, persistent, or recurring symptoms (compare acute)
virus transmission characterized by a long period of acquisition followed by a latent period of several hours before the vector is able to transmit the virus; retention of the virus by the vector can be a long period, usually several days; the virus circulates in the body of the vector
a curled, tendril-like mass of exuded spores, held together by a slimy matrix
a bridge between hyphal cells; occurs in Basidiomycetes,
club-shaped
cleistothecium: (pl. cleistothecia):
a spherical, closed ascocarp
n. a population of cells or organisms of identical genotype; 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 vectorgrow together into one spot
the protective protein layer that surrounds the nucleic acid of a virus
a spherical (or near-spherical) bacterial cell
a particular sequence of three nucleotides in a nucleic acid that codes for a specific amino acid or termination of a polypeptide chain
a group of fungi in the Deuteromycetes that produce pycnidia or acervuli (compare Hyphomycetes)
having multiple nuclei embedded in cytoplasm without cross walls; nonseptate
the portion of the seedling or plant near the soil surface
establishment and ramification of a pathogen within a host plant; occurs after infection
to ramify through plant tissue via growth of a pathogen
growth of a microorganism in mass, especially as a pure culture
colony forming unit: (abbr. cfu):
the number of colonies formed per unit of volume or weight of a cell or spore suspension
isolation of a specific tissue area by host barrier tissues
prevents growth and reproduction of the pathogen such that pathogen populations decline very sharply. Complete resistance is almost always resistance to the pathogenone circle within another with a common center
the formation of asexual spores (conidia)
simple or branched hypha on which conidia are produced
an asexual, nonmotile fungal spore
the temporary contact of bacterial cells during which genetic material is transferred (directed by plasmids)
conk:
a shelf-like, typically hardened basidiocarp of a wood decaying fungus, usually a polypore
growing the same crop in the same location repeatedly
coremium: (pl. coremia; syn. synnema):
compact or fused, generally upright conidiophores, with branches and spores forming a headlike clustercork:
external protective tissue of a stem or root, impermeable to water and gasses; the primary component of bark; also a structural wound response in many plantsregion of parenchyma tissue between the epidermis and the phloem in stems and roots; region beneath the rind of a sclerotiuma seed leaf, one in moncots and two in dicots;
the successive planting of different crop species in an area; used to improve soil fertility and reduce disease and pest problems
a process in which sexual reproduction occurs as a result of the fusion of sex cells from different individuals
transfer of pollen from the anthers of one flower to the stigma of another flower
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 pathogenupper dome of tree, bearing leaves, flowers, and fruits; or junction of root and stem of a plant, usually at the soil line;
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)how plants are grown, including application of nutrients, irrigation practices, types of cultivation, etc.; also a method used for disease managementgrowth and propagation of microorganisms on nutrient media; growth and propagation of living plants
noncellular outer layer of an insect or a nematode; water-repellent, waxy layer of epidermal cells of plant parts, such as leaves, stems and fruitcv.: (abbr. for cultivar; syn. variety):
a cultivated variety of a plant species with recognizable characteristics
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 conditionsplant hormones (growth regulators) that control cell division and are important for shoot stimulation of callus tissue
the study of changes induced by disease at the cellular level
living protoplasm in a cell, except the nucleus
cytoplasmic inheritance: (maternal inheritance):
inheritance of genes not located in the nucleus, i.e. those in mitochondria and chloroplasts
death of a seedling before (preemergence damping-off) or shortly after emergence (postemergence damping-off)
decomposition of organic matter
a plant that sheds its leaves completely at the end of its annual growth period
loss of leaves from a plant, whether normal or premature
a rust fungus that lacks the urediniospore
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) baseto dry out
Deuteromycetes: (syn. Fungi Imperfecti):
group of fungi without a sexual stage; also, the asexual (anamorph) stage of many Ascomycetes and Basidiomycetesthe art of identifying a disease by the symptoms and signs present
branching, often successively, into two arms
plant with two cotyledons or seed leaves
plant disease symptom where one or more individual stems or branches start to die at the tip, with the disease spreading down toward the base of the stem.
a plant that is used to distinguish between different various strains or races of a given plant pathogen
a culture medium that is used to distinguish between organisms that can grow on it based on colony morphology or other recognizable phenotypeshaving two different but sexually compatible haploid nuclei per cell; common in many Basidiomymetes
having two complete sets of chromosomes (2N)
group of Ascomycetes that produces asci in a cup-like ascocarp called an apothecium
abnormal functioning of an organism caused by the continuous irritation by a primary causal agent that results in production of symptoms
sequence of events a pathogen follows to complete its life cycle on a host plant
number or percentage of plants affected by a disease within a population
refers to the addition of time to the disease triangle to indicate disease is not static; it develops over time
the level or intensity of damage done by a disease
refers to the three components necessary for disease to occur: susceptible plant, pathogen and favorable environment
to eliminate a pathogen from infected plant tissues
to kill pathogens that have not yet initiated disease, or other contaminating microoganisms that occur in or on inanimate objects as such soil or tools, or that occur on the surface of plant parts such as seeddispersal: (syn. dissemination):
spread of infectious material or pathogen parts (inoculum) from diseased to healthy plants
dissemination: (syn. dispersal):
spread of infectious material or parts of the pathogen (inoculum) from diseased to healthy plants
a parasitic seed plant, genus Cuscuta spp., that lacks leaves but has flowers; the yellow filamentous vines are first observed as clumps growing over plantsdescribes a phenotypic trait that is expressed in hybrid progeny of diploid organisms even when contributed by only one of the parents (compare recessive)"resting" period when growth slows almost to a halt; usually occurs during the dry or cold season of the year.a reversible condition of suspended growth and reduced metabolism of an organism, generally induced by internal factors or environmental conditions as a mechanism of survivala plant disease in which the fungus appears as a downy growth on the host surface; caused by a member of the Oomycetes
single gene resistance that has been stable; no races have ever developed that can overcome the resistance. This is a goal of plant breeding, but you do not know if a gene will be durable unless you deploy it in a population of the pathogen.underdevelopment of a plant or plant organs, which may be caused by disease, inadequate nutrition, or unfavorable environmental conditionsectomycorrhiza: (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 endomycorrhiza)parasite that feeds from the exterior of its host (compare endoparasite)
fungal development outside the root surface
blisters produced on leaves and other plant parts under conditions of high moisture and restricted transpiration
group of eggs held together by a gelatinous matrix; common in root-knot and other nematodes
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 reactantsgrowth of a seedling shoot through the soil surface
abnormal outgrowth from the surface of a stem or leaf
to cover a virus nucleic acid with a protein coat
to form a cyst or protective covering; produce a cell wall in the case of motile zoospores
native to a particular place; pertaining to a low and steady level of natural disease occurrence
endoconidium: (pl. endoconidia):
a conidium produced inside a hypha or conidiophore
layer of cells within the root that separates the vascular tissue and the cortex
endomycorrhiza: (pl. endomycorrhizae; syn. vesicular-arbuscular mycorrhiza, VA mycorrhiza):
symbiotic association between a nonpathogenic or weakly pathogenic fungus and the roots of plants in which fungal hyphae invade cortical cells of the rootparasitic organism that lives and feeds from inside its host (compare ectoparasite)
plant developing inside another organism; also used for endoparasitic fungi found in grass species
resistant, thick-walled asexual spore formed within a bacterial or fungal cell
protein that catalyzes a specific biochemical reaction
enzyme-linked immunosorbent assay: (acronym ELISA):
a serological test in which the sensitivity of the reaction is increased by attaching an enzyme that produces a colored product to one of the reactantsEPA: (acronym for Environmental Protection Agency):
the federal agency responsible for controlling the various aspects of air, water, and soil pollution, including pesticide regulationsan increase of disease in a population; a general and serious outbreak of disease (epiphytotic)
epidemiology: (adj. epidemiologic):
the study of factors influencing the initiation, development, and spread of infectious disease; the study of disease in populations of plantssurface layer of cells of leaves and other plant parts
abnormal, downward curling of a leaf, leaf part, or stem
on the upper surface of a leaf
organism growing on a plant surface, but not as a parasite
living on the surface of plants, but not as a parasite
an epidemic in a plant population
control of plant disease by eliminating the pathogen after it is established or by eliminating the plants that carry the pathogen
a disease of certain grasses and cereals, especially rye, caused by Claviceps spp.; a sclerotium, or resting structure, produced by Claviceps species and other closely related fungi in infected flowers of parasitized grain plantsa 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 Agesbursting or erupting through the substrate surface
failure of inherently susceptible plants to become diseased, even though disease is prevalent
a plant hormone influencing various aspects of vegetative growth, fruit ripening, abscission of plant parts, and the senescence of flowerselongation of stems caused by reduced light intensities
the study of the causes of diseases
an organism containing a membrane-bound nucleus and other organelles, i.e. all higher plants, animals, fungi, and protists (see prokaryote)control of disease by excluding the pathogen or infected plant material from crop production areas (e.g. by quarantines and embargoes)outside a cell
extrachromosomal inheritance: (also cytoplasmic or maternal inheritance):
inheritance of genes not located in the nucleus, i.e. those in mitochondria and chloroplastsliquid excreted or discharged from diseased tissues, from roots and leaves, or by fungi
f. sp.: (abbr. for forma specialis):
a taxonomic group within a pathogenic species defined in terms of host range, i.e. members of different formae speciales infect different groups of plantscapable of changing life-style, e.g. from saprophytic to parasitic or the reverse
organism that is normally saprophytic but is capable of being parasitic
organism that is normally parasitic but is capable of being saprophytic
cultivated land kept free from a crop or weeds during the normal growing season
malformation in shoots or floral organs manifested as enlargements and flattening as if several parts were fused
in reference to prokaryotic organisms, having special growth and nutritional requirements
Federal Food, Drug, and Cosmetic Act (acronym FFDCA):
the federal law which sets legal tolerances of pesticides on food products at harvest
Federal Insecticide, Fungicide, and Rodenticide Act (acronym FIFRA):
the federal law which legislates the conditions for use of pesticides
fine root that absorbs water and dissolved nutrients
threadlike
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 generationwilted, lacking turgor
flag:
isolated, wilted or necrotic branch with dead leaves attached
hairlike, whiplike, or tinsel-like appendage of a motile cell, bacterium or zoospore that provides locomotion
minute, discolored spot in green tissue
capable of bending; with turns
small area of diseased plants within a population
pertaining to leaves
Food Quality Protection Act (acronym FQPA):
the federal law which sets a health-based standard governing pesticide tolerance levels in fooda 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 plantsany of various complex, spore -bearing fungal structures
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
chemical used to control fungal diseases. Despite the name, most fungicides only slow down or prevent the spread of disease; only a few actually kill the fungus.chemical used to control fungal diseases. Despite the name, most fungicides only slow down or prevent the spread of disease ; only a few actually kill the fungus.chemical or physical agent that kills or inhibits the growth of fungi
fungistat: (adj. fungistatic):
compound that inhibits fungal growth or sporulation but does not cause death
spindle-shaped; tapering at each end
insect tunnel in bark and wood
cell containing gametes or nuclei that act as gametes
sex cell
gene:
unit within an organism controlling heritable characteristics; genes are organized on chromosomes
the hypothesis that corresponding genes for resistance and avirulence exist in the host and pathogen, respectively
relating to heredity; referring to heritable characteristics
the system of triplet codons composed of nucleotides of DNA or RNA that determine the amino acid sequence of a protein
the transfer of specific genes between organisms using enzymes and laboratory techniques rather than biological hybridizationthe complete genetic information of an organism or virus
genetic constitution of an individual or group; class or group of individuals sharing a specific genetic makeup (see phenotype )
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 binomialthe theory that infectious or contagious diseases are caused by microorganisms (germs)
hypha resulting from an outgrowth of the spore wall and cytoplasm after germination
begin growth (as of a seed, spore, sclerotium, or other reproductive body)
bearer of heredity material, often loosely applied to cultivars and breeding lines
enlarged, multinucleate cell formed in roots by repeated nuclear division without cell division induced by secretions of certain sedentary plant-parasitic nematodesplant hormones (growth regulators) that affect stem elongation
to circle and cut through a stem or the bark and outer few rings of wood, disrupting the phloem and xylem
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 hostprocedure 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 bacteriabacteria staining red or pink in the Gram staining procedure after treatment with Gram's stain
bacteria staining violet or purple in the Gram staining procedure after treatment with Gram's stain
containing an egg or eggs; capable of depositing eggs
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 gibberellinspaired, specialized, epidermal cells that contain chloroplasts and surround a stoma
gum:
gelatinous, sugary aggregate that is synthesized and exuded by plant tissues
pathologic condition characterized by excessive formation of gums; the products of cell degeneration
exudation of watery, sticky liquid from hydathodes, especially along leaf margins
a place with a particular kind of environment suitable for the growth of an organism
having a single complete set of chromosomes
ability to withstand stress; often used to refer to cold hardiness
specialized branch of a parasite formed inside host cells to absorb nutrients (PDF);
head:
in plants, a type of inflorescence in which numerous small flowers are densely crowded on a disk or around a central stalk
central cylinder of nonfunctional xylem in a woody stem (see sapwood)
an organism that lives on living cells for a period of time prior to becoming a necrotroph
describing primary, soft, nonwoody tissue, as a plant or plant part; having the characteristics of an herb
a chemical used for killing plants or inhibiting plant growth, e.g. a weed or grass killer
a measure of the ability of a characteristic to be passed from one generation to the next
hermaphrodite (adj. hermaphroditic):
having both male and female reproductive organs
pertaining to a rust fungus requiring two unrelated host plants for completion of its life cycle (see autoecious)
heterokaryon (adj. heterokaryotic):
cell with genetically different nuclei
heterosis (syn. hybrid vigor):
increased vigor of hybrid offspring when compared to either parent
heterothallism (adj. heterothallic):
condition in which sexual reproduction can occur only in the presence of genetically different mycelia (see homothallism)an organism that obtains nourishment from outside sources and must obtain its carbon from organic carbon compounds (see autotroph )having alternate forms (allele) of a gene on homologous chromosomes (see homozygous)
the whole fungus in all its states (see anamorph, teleomorph)
homothallism (adj. homothallic):
condition in which sexual reproduction occurs with a single thallus; self-fertile (see heterothallism)
having the same form (allele) of a gene on homologous chromosomes (see heterozygous)
sugary ooze or exudate, often from aphids, and a characteristic symptom of ergot disease
resistance conferred by multiple minor genes; this resistance is usually partial but effective against most or all races or strains (genetic variants) of a pathogen (see 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 gibberellinsliving plant attacked by or harboring a parasite or pathogen and from which the invader obtains part or all of its nourishment
the range of plants on which an organism, particularly a parasite, feeds
transparent or nearly so; translucent; often used in the sense of colorless
offspring of two individuals of different genotypes
epidermal leaf structure specialized for secretion or exudation of water; leaf opening at terminus of vein
continuous, spore-bearing layer of a fungus fruiting body
organism that is parasitic upon another parasite
hyperplasia (adj. hyperplastic):
abnormal increase in the number of cells, often resulting in the formation of galls or tumors
extremely or excessively sensitive; often refers to an extreme reaction to a pathogen known as the Hypersensitive Reaction
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
imperfect fungi that produce conidia freely or on a sporodochium or synnema (see Coelomycetes)
portion of the stem below the cotyledons and above the root (see epicotyl)
(hypo=less than) a reduced ability to cause disease; a strategy used in biocontrol
icosahedral: (n. icosahedron):
having 20 faces, as a polyhedral-shaped virus particle (see isometric )
cannot be infected by a given pathogen
a detection method based on antibodies specifically selected to react with the substance to be detected (the antigen)
imperfect state (syn. anamorph):
the asexual form in the life cycle of a fungus, when asexual spores (such as conidia) or no spores are producedin its original place or environment
in glass, on artificial media, or in an artificial environment; outside the host
within a living organism
structure developed within a plant cell as a result of infection by a virus, often useful in identifying the virus
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 individualthe time between penetration of a host by a pathogen and the first appearance of disease symptoms
testing of a plant for infection, often by mechanical transmission or by grafting tissue from it to an 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 factorprocess in which an organism enters, invades, or penetrates and establishes a parasitic relationship with a host plant
site in or on a host plant where infection can occur
organized mass of hyphae formed on the surface of a plant from which numerous infective hyphae develop
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
pertaining to disease, capable of spreading from plant to plant
referring to an organism able to attack a host and cause infection; referring to a vector carrying or containing a pathogen and able to transfer it to a host plantto attack as a pest (used especially of insects and nematodes); to contaminate, as with microorganisms; to be present in large numbersinitial 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 seasondamage caused by transitory interaction with an agent such as an insect, chemical, or unfavorable environmental condition
to place inoculum in an infection court; to insert a pathogen into healthy tissue
pathogen or its parts, capable of causing infection when transferred to a favorable location
a measure of the number of propagules of a pathogenic organism per unit area or volume
integrated pest management (abbr. IPM):
a combination of strategies to reduce losses due to pests and pathogens based on environmental and economic considerationsbetween or among cells
to grow two or more crops simultaneously on the same area of land
the portion of a stem between two successive nodes
between (leaf) veins
through or within cells
(n.) a culture or subpopulation of a microorganism separated from its parent population and maintained in some sort of controlled circumstance; (v.) to remove from soil or host material and grow in pure cultureusually used for virus particles to describe those that are icosahedral in structure and appear approximately round
the fusion of nuclei
knot:
gall; a localized abnormal swelling
the procedure used to prove the pathogenicity of an organism, i.e. its role as the causal agent of a disease
expanded part of a leaf (see petiole)
present but not manifested or visible, as a symptomless infection by a pathogen
infection unaccompanied by visible symptoms
the time between infection and the appearance of symptoms and/or the production of new inoculum (sometimes synonymous with incubation period); the time after a vector has acquired a pathogen and before it can be transmittedLD50 (abbr. for lethal dose 50%):
a measure of relative acute toxicity; the lethal dose of a compound that causes death in 50% of the test animals treateda plant disease lesion typically restricted in development in the leaf after reaching a characteristic size
a natural opening in the surface of a stem or tuber, fruit or root for gas exchange
localized diseased area or wound
the cyclical stages in the growth and development of an organism
hardening of tissue through the deposition of lignin in the cell wall
complex organic substance or group of substances that impregnate the cell walls of xylem vessels and certain other plant cells; constitutes woodsmall, restricted lesion, often the characteristic reaction of differential cultivars to specific pathogens, especially in response to mechanical inoculation with a virusto fall over
along the long axis of an organism or object
central cavity of a cell or other structure
to cause disintegration of tissues by separation of cells; to soften by soaking
macroconidium (pl. macroconidia):
the larger of two kinds of conidia formed by certain fungi (see microconidium)
a rust fungus that typically exhibits all five stages of the rust life cycle (see demicyclic, microcyclic)
an element needed in relatively large quantities for plant growth, e.g. nitrogen (N), phosphorus (P), and potassium (K); (see micronutrient)maternal inheritance (also cytoplasmic or extrachromosomal inheritance):
inheritance of non-nuclear genes, i.e. those in mitochondria and chloroplastscompatible strains, usually designated + and
injury of a plant part by abrasion, mutilation, or wounding
spread or introduction of inoculum to an infection court (wounding) by human manipulation, accompanied by physical disruption of host tissuesa 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 growingprocess 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)pertaining to or relating to microbes, or microorganisms
weather conditions on a small scale, e.g. at the surface of the plant or within a crop
microconidium (pl. microconidia):
the smaller of two kinds of conidia formed by certain fungi (see macroconidium)
describing a rust fungus that produces only teliospores and basidiospores (see demicyclic, macrocyclic)
the combination of all microorganisms in a particular environment
one millionth of a meter
an essential element needed by plants for growth and required in very small amounts (see macronutrient)
an organism of such small size that it can only be seen as an individual organism with the aid of microscopemicroscopic, dense aggregate of darkly pigmented, thick-walled hyphal cells
an instrument used to see small objects clearly by using light and lenses to magnify an object
the layer, consisting largely of pectic substances, between the walls of adjacent plant cells
migrating from place to place on a plant or from plant to plant when feeding (see sedentary)
thin coating of mycelial growth and spores on the surfaces of infected plant parts
nuclear division in which the chromosome number remains the same (see meiosis)
MLO (syn. mycoplasmalike organsim):
archaic term for phytoplasma; plant-parasitic pleomorphic mollicute (prokaryote with no cell wall) found in phloem tissue; cannot yet be grown on artificial nutrient mediamold:
any microfungus with conspicuous, profuse, or woolly superficial growth (mycelium and/or spore masses) on various substrates; especially an economically important saprobe; molds commonly grow on damp or decaying matter and on the surface of plant tissuesone of a group of prokaryotic organisms bounded by flexuous membranes and lacking cell walls (see phytoplasma and spiroplasma)molt:
to shed a cuticle or body encasement during a phase of growth
antibody produced from clones of a single antibody-producing cell (see polyclonal antibody)
plant with one cotyledon, such as grasses, grain crops, corn (see dicot)
the growth of the same plant species in close proximity, with few or no other types of plant present
having one disease or life cycle per growing season (see polycyclic)
having male and female reproductive organs on a single individual (see dioecious)
determined by a single gene (see polygenic)
a culture containing one species of organism growing in the presence of one other species of organism
morphology (adj. morphologic):
the study of the form of organisms; form and structure of organisms
disease symptom characterized by non-uniform coloration, with intermingled normal, light green and yellowish patches, usually caused by a virus; often used interchangeably with mottledisease symptom comprising light and dark areas in an irregular pattern, usually caused by a virus; often used interchangeably with mosaicfor viruses, a protein encoded by the pathogen that is required for spread within an infected plant
viscous, slimy
layer of material, such as organic matter or plastic, applied to the surface of the soil for purposes such as retention of water and inhibition of weedscomposed of many cells (see unicellular)
having more than one nucleus per cell (see uninucleate)
having many septa or crosswalls
a dried shriveled fruit; plant part or organ partially or completely replaced with fungal structures
a fleshy fruiting body of a fungus, especially of a Basidiomycete of the family Agaricaceae
a substance that causes a mutation
an abrupt heritable or genetic change in a gene or an individual as a result of an alternation in a gene or chromosome, or of an increase in chromosome numbera group in the Fungi Imperfecti that does not produce spores, but may produce chlamydospores or sclerotia, e.g. Rhizoctonia and Sclerotium; subsequent research has defined sexual reproduction for some speciesmycelium (pl. mycelia, adj. mycelial):
mass of hyphae constituting the body (thallus) of a fungus
the study of fungi
a fungus that attacks another fungus
mycoplasmalike organism (syn. MLO):
archaic term for phytoplasma; plant-parasitic pleomorphic mollicute (prokaryote with no cell wall) found in phloem tissue; cannot yet be grown on artificial nutrient mediamycorrhiza (pl. mycorrhizae; adj. mycorrhizal):
symbiotic association between a nonpathogenic or weakly pathogenic fungus and the roots of plants (see ectomycorrhiza and endomycorrhiza)poisonous compound produced by a fungus
a virus that infects fungi
Myxomycetes (syn. slime molds):
saprophytic organisms that form vegetative amoeboid plasmodia and spores
death of cells or tissue, usually accompanied by black or brown darkening
a parasite that typically kills and obtains its energy from dead host cells (see biotroph)
a nectar-secreting gland in a flower
ribonucleic acid complimentary to the positive or plus sense; not translated into protein (see positive sense RNA )
agent, usually a chemical, that kills nematodes
nonsegmented roundworm (animal), parasitic on plants or animals, or free living in soil or water
small knot or irregular, rounded lump; on leguminous plants, structures on roots that contain nitrogen-fixing bacteriathe scheme by which names are attached to objects, including organisms
a disease that is caused by an abiotic agent that cannot be transmitted from one plant to another
unable to cause disease
nonpersistent transmission (syn. stylet-borne transmission):
a type of virus transmission in which the virus is acquired and transmitted by the vector after short feeding times, and is retained by the vector for only a short period of timewithout cross-walls; coenocytic
a cultural system most often used with annual crops, in which the new crop is seeded or planted directly in a field on which the preceding crop plants were cut down, had the tops harvested, or were destroyed by a nonselective herbicide (the old crop is not removed or incorporated into the soil as is common in preparing a plant bed)genetic material of all living organisms, including DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)
obligate parasite (syn. biotroph):
organism that can grow only as a parasite in association with its host plant and cannot be grown in artificial culture mediablock or plug that stops flow of liquids (as in vessels)
oedema (also edema; syn. intumescence):
blisters produced on leaves and other plant parts under conditions of high moisture and restricted transpirationfemale gametangium of Oomycetes, containing one or more gametes
class of fungal-like organisms typically with nonseptate mycelium, asexual sporangia and zoospores, and sexual oospores
thick-walled, sexually-derived resting spore of Oomycetes
ooze:
mass of bacterial cells mixed with host fluids
a pore; an opening in the papilla or neck of a perithecium, pseudothecium, or pycnidium through which spores are released
to survive or persist from one planting season to the next
to survive or persist through the winter period
a highly reactive form of oxygen (O3) that may injure plants
a protective layer of ozone in the upper atmosphere that reduces ultraviolet radiation
PAN (abbr. for peroxyacetyl nitrate):
a component of smog formed when the exhaust of automobiles and other internal combustion engines is in the presence of sunlighta widespread and destructive outbreak of disease simultaneously in several countries
having the antheridium contact the oogonium on the side, as in many Pythium sp. (see amphigynous)
organism that lives in intimate association with another organism on which it depends for its nutrition; not necessarily a pathogenparthenogenesis (adj. parthenogenetic):
reproduction by the development of an unfertilized egg
resistance that is not complete. Partial resistance is resistance that is quantitatively expressed (levels of resistance), but not necessarily quantitatively inherited. Partial resistance most likely incorporates mechanisms of resistance to the pathogen and disease.to free a material, usually a liquid, of selected harmful microorganisms using heat
an entity, usually a microorganism, that can incite disease .
stages in disease development
ability to cause disease
the study of diseases
a subdivision of a pathogen species characterized by its pattern of virulence or avirulence to a series of differential host varieties
a subdivision of a plant pathogenic bacterial species defined by host range; pathovar for bacteria is equivalent to forma specialis for fungia methylated polymer of galacturonic acid found in the middle lamella and the primary cell wall of plants; jelly-forming substance found in fruitinitial invasion of a host by a pathogen
penetration peg (syn. infection peg):
the specialized, narrow, hyphal strand on the underside of an appressorium that penetrates host cells
antibiotic produced by certain species of Penicillium and effective against Gram-positive bacteria
something that occurs year after year; plant that survives for several to many years (see annual, biennial)
sexual; capable of sexual reproduction (see teleomorph)
perfect state (syn. teleomorph):
the sexual form in the life cycle of a fungus (see anamorph)
flask-shaped or subglobose, thin-walled fungus fruiting body (ascocarp) containing asci and ascospores; spores are released through a pore (ostiole) at the apexhaving hairs or flagella distributed over the whole surface
persistent transmission (syn. circulative transmission):
a type of virus transmission in which the virus is acquired and transmitted by the vector after relatively long feeding times and remains transmissible for a prolonged period while in association with its vectorpest:
any organism that damages plants or plant products
a chemical used to control pests
pH:
negative logarithm of the effective hydrogen ion concentration; a measure of acidity (pH 7 is neutral; values less than pH 7, acidic; greater than pH 7, alkaline)cork; a protective tissue composed of nonliving cells with suberized walls produced by the phellogen and accumulating on the surface of stems and rootstissue formed by and internal to the phellogen ; resembles the cortical parenchyma in morphology
cork cambium; lateral meristem forming the periderm, a protective tissue in stems and roots; phellem (cork) is produced toward the surface, phelloderm toward the insideexternal, visible physical characteristics of an organism determined by the interaction of its genotype with the environment (see genotype)end cell of a conidiophore with one or more open ends through which a basipetal succession of conidia develops
food-conducting, food-storing tissue in the vascular system of roots, stems, and leaves
product of photosynthesis
manufacture of carbohydrates from carbon dioxide and water in the presence of chlorophyll (s), using light energy and releasing oxygenarchaic term for a member of a group of fungi without cross walls (septa) in their mycelium
change of floral organs to leaflike structures
arrangement of leaves on a stem in relation to one another
substance produced in higher plants in response to a number of chemical, physical, and biological stimuli that inhibits the growth of certain micro-organismsable to cause disease in plants
phytopathology (syn. plant pathology):
the study of plant diseases
phytoplasma (syn. mycoplasmalike organism, MLO):
plant-parasitic pleomorphic mollicute (prokaryote with no cell wall) found in phloem tissue; cannot yet be grown on artificial nutrient mediaharmful to plants (usually used to describe chemicals)
plant pathology (syn. phytopathology):
the study of plant diseases
a circular, self-replicating hereditary element that is not part of a chromosome; plasmids are used in recombinant DNA experiments as acceptors and vectors of foreign DNAplasmodesma (pl. plasmodesmata):
cytoplasmic strands that connect living cells
naked multinucleate mass of protoplasm moving and feeding in amoeboid fashion
the fusion of two sex cells
shrinking of a protoplast due to water loss from the vacuole of a plant cell
able to assume various shapes (and perhaps sizes); occurrence of more than one distinct form in the life cycle of an organism
the number of (complete) sets of chromosomes in a cell, e.g. haploid, diploid, polyploid
at one end or pole of the cell
a preparation containing antibodies against more than one epitope of an antigen (see monoclonal antibody)
having several to many disease cycles in a growing season (see monocyclic)
requiring more than one year to complete one life or disease cycle
pertaining to, or governed by, many genes (see monogenic )
having three or more complete sets of chromosomes (see haploid, diploid )
simple, fleshy, indehiscent fruit derived from several carpels, e.g. apple, pear, quince
RNA that can serve directly as messenger RNA (see negative sense RNA)
a white, powdery, superficial ascomycetous fungus that is an obligate parasite and generally is found only on one or a few closely related species of plantsto make prone to infection and disease
an increase in susceptibility resulting from the influence of wounds or the environment
primary inoculum (syn. initial inoculum):
inoculum, usually from an overwintering source, that initiates disease in the field, as opposed to inoculum that spreads disease during the seasonwithout internal membrane-bound organelles, lacking a distinct nucleus, such as bacteria and mollicutes (see eukaryotic)in rust and smut fungi, a germ tube issuing from the teliospore and bearing the basidiospores
any part of an organism capable of independent growth
agent, usually a chemical, applied to a plant surface in advance of a pathogen to prevent infection
a principle of plant disease control in which a barrier is placed between the susceptible plant and pathogen (e.g. the use of protective chemical dusts or sprays)a nitrogen-containing organic compound composed of units called amino acids
living contents of a cell
living cell exclusive of a wall
nearest to the point of attachment (see distal)
pseudothecium (pl. pseudothecia):
perithecium-like fruiting body containing asci and ascospores dispersed rather than in an organized hymenium; an ascostroma with a single locule or cavity and containing bitunicate ascithe region through which rust urediniospores move from southern areas through all grain-producing areas of the United States to Canada each seasonsmall blisterlike elevation of epidermis formed as spores emerge
small fruiting bodies of rust fungi that erupt through the surface of a leaf.
a subdivision of a plant pathogenic bacterial species defined by host range; pathovar for bacteria is equivalent to forma specialis for fungi(pl.) a tiny, dark, round fruiting body of a fungus. Produces conidia.
spore (conidium) produced in a pycnidium
asexual, globose or flask-shaped fruiting body of certain imperfect fungi producing conidia
pycniospore (syn. spermatium):
haploid, sexually derived spore formed in a pycnium of rust fungi
pycnium (pl. pycnia; syn. spermagonium):
globose or flask-shaped haploid fruiting body of rust fungi bearing receptive hyphae and pycniosporeslegislative control of the transport of plants or plant parts to prevent the spread of pests or pathogens
dormant or inactive
race:
subgroup or biotype within a species or variety, distinguished from other races by virulence on certain genotypes (symptom expression, or host range), but not by morphologythe part of a rust fungus pycnium (spermogonium) that receives the nucleus of a pycniospore (spermatium)
a phenotypic trait that is expressed in diploid organisms only if both parents contribute the trait to the progeny
DNA molecules in which sequences, not normally contiguous, have been placed next to each other by in vitro methods
i) the process by which a DNA or RNA molecule makes an exact copy of itself; ii) repetition of an experiment or procedure at the same time and place (one of several identical experiments, procedures, or samples); iii) the process by which a virus particle induces the host cell to reproduce the virusability of a plant to prevent or impede disease development (see susceptible)
spore, often thick-walled, that can remain alive in a dormant state for a long period of time
enzyme that cleaves DNA at a particular base sequence; sometimes referred to as a restriction enzyme
having netlike markings
genus of bacteria that lives symbiotically with roots of leguminous plants; during the symbiosis, atmospheric nitrogen gas is converted into a form useable by the plantgalls on roots caused by Rhizobium spp.
underground stem that is mostly horizontal, jointed, fleshy, and often elongated
macroscopic rope-like strand of compacted hyphal tissue formed by certain fungi
zone of soil under the influence of the root; soil immediately around plant roots
ribonucleic acid: (abbr. RNA):
several nucleic acids composed of repeating units of ribose (a sugar), a phosphate group, and a purine (adenine or guanine) or a pyrimidine (uracil or cytosine) base; transcribed from DNA and involved in translation to proteinsRNA molecules forming part of the ribosomal structure
a subcellular protoplasmic particle, made up of one or more RNA molecules and several proteins, involved in protein synthesis
disease symptom characterized by yellowish or necrotic rings enclosing green tissue, as in some plant diseases caused by viruses
to remove and destroy individual plants that are diseased, infested by insects, or otherwise undesirable
a group of cells on a root that protects the growing tip
the various compounds that leak from growing and expanding sections of roots (zon of elongation) as well as from broken cells and at exit points of lateral rootsthe fusion of roots of two adjacent plants so that their water and food conducting (vascular) systems become joined
threadlike, single-celled outgrowths from a root epidermal cell
reduction of root volume, which becomes brittle and brown to reddish-brown in color. Diseased tissue may be isolated or include the entire root system. Results in limited water and nutrient uptake.portion of the stem (trunk) and the associated root system into which a bud or scion is inserted in grafting
disease symptom characterized by short, bunchy growth habit due to shortened internodes and no comparable reduction in leaf size
rot:
softening, discoloration, and often disintegration of plant tissue as a result of fungal or bacterial infection
growth of different kinds of crops in succession in the same field
wrinkled, roughened
brownish, roughened areas resulting from cork formation