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


(pl. acervuli)

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


having a pH of less than 7


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


occurring in the air


living only in the presence of oxygen


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


having basic (non-acidic) properties; pH greater than

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


living in the absence of oxygen


(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)


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


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


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


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


shaped like short rods with rounded ends

bacterial streaming

large populations of bacteria that exude from the cut surface of infected plant tissue 


(pl. bacteria)  
a prokaryotic, microscopic, single-celled organism with a cell wall that increases by binary fission


(syn. obligate parasite)  
an organism that can live and multiply only on another living organism (see necrotroph)


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


necrotic area of tissue irregular in form


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


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


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


the expanded leafy top of a plant or plants

causal agent

organism or agent that incites and governs disease or injury


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.


(or chimaera)

plant or organ consisting of two or more genetically different tissues


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


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


grow together into one body or spot


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


one circle within another with a common center


simple or branched hypha on which conidia are produced


(pl. conidia)
an asexual, nonmotile fungal spore that develops externally or is liberated from the cell that formed it

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


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


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


(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


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


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


loss of leaves from a plant, whether normal or premature


to dry out


(n. diagnosis)
a distinguishing characteristic important for the identification of a disease or other 


(v. die back)
progressive death of shoots, leaves, or roots, beginning at the tips

direct penetration

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


abnormal functioning of an organism

disease incidence

number of plants affected by a disease within a population


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


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


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

downy mildew

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

drift (of pesticides)

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


insufficient soil water for normal plant growth


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


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

egg mass

group of eggs held together by a gelatinous matrix


(acronym for Enzyme-Linked Immuno Sorbent 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


growth of the seedling shoot through the surface of the soil


abnormal outgrowth from the surface of a stem or


protein that catalyzes a specific biochemical reaction


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


(adj. epidemiologic)
the study of factors influencing the initiation, development, and spread of infectious disease; the study of disease in populations of plants


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


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


elongation of stems caused by reduced light intensities


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


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


minute, discolored spot in green tissue


pertaining to leaves

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

free water

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


(adj. fungicidal)
chemical or physical agent that kills or inhibits the growth of fungi


(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


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


insect tunnel in bark and wood


relating to heredity; referring to heritable characteristics


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


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


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

host range

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


(v. hybridize)
offspring of two individuals of different genotypes


(pl. hyphae; adj. hyphal)  
single, tubular filament of a fungal thallus or mycelium; the basic structural unit of a fungus


cannot be infected by a given pathogen

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


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

indirect penetration

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


produced in response to a stimulus (see constitutive)


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

infection period

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


pertaining to disease, capable of spreading from plant to plant


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


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


flower or flower cluster

initial inoculum

(syn. primary inoculum)
inoculum, usually from an overwintering source, that initiates disease in the field, as opposed to inoculum that spreads disease during the season


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


(pl. inocula)
pathogen or its parts, capable of causing infection when transferred to a favorable location

inoculum density

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


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

integrated pest management

(abbr. IPM)
a combination of strategies to reduce losses due to pests and pathogens based on environmental and economic considerations


between or among cells


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


(adj. internodal)
the portion of a stem between two successive nodes


between (leaf) veins


through or within cells


(abbr. for integrated pest management)
a combination of strategies to reduce losses due to pests and pathogens based on environmental and economic considerations


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


gall; localized abnormal swelling

Koch's postulates

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


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


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

latent infection

infection unaccompanied by visible symptoms

latent period

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

leaf sheath

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

leaf spot

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


mobile insects with sucking mouthparts (order Homoptera)


one of the separate blades or divisions of a compound leaf


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


simple, dry, dehiscent fruit developed from a simple pistil and splitting at maturity along two seams;
a plant of the family Fabaceae (formerly Leguminosae)


localized diseased area or wound

local lesion

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


to fall over


 an element needed in relatively large quantities for plant growth, e.g. nitrogen (N), phosphorus (P), and potassium (K); (see micronutrient)

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


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


(syn. microbe)
an organism of such small size that it can only be seen as an individual organism with the aid of microscope


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


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


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



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


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


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


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


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


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


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


composed of many cells (see unicellular)


(pl. mycelia, adj. mycelial)  
mass of hyphae constituting the body (thallus) of a fungus\


(adj. necrotic)  
death of cells or tissue, usually accompanied by black or brown darkening


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


agent, usually a chemical, that kills nematodes


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


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)


(adj. nodal)
enlarged portion of a shoot at which leaves or buds arise


(v. nodulation)  
small knot or irregular, rounded lump; on leguminous plants, structures on roots that contain nitrogen-fixing bacteria

noninfectious disease

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


(syn. avirulent)
unable to cause disease

nonpersistent transmission

(syn. stylet-borne transmission)
a type of virus transmission in which the virus is acquired and transmitted by the vector after short feeding times, and is retained by the vector for only a short period of time

obligate parasite

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


(adj. oomycetous)
class of fungal-like organisms typically with nonseptate mycelium, asexual sporangia and zoospores, and sexual oospores


thick-walled, sexually-derived resting spore of oomycetes


mass of bacterial cells mixed with host fluids


describing a molecule containing carbon atoms; pertaining to living organisms


to survive or persist through the winter period


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


(adj. pathogenic)
a disease-producing organism or agent


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


(acronym for polymerase chain reaction)
a technique used to amplify the number of copies of a specific region of DNA in order to produce enough of the DNA for use in various applications such as identification and cloning


initial invasion of a host by a pathogen

persistent transmission

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


any organism that damages plants or plant products


a chemical used to control pests


stalk portion of a leaf (see lamina)


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


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

phloem necrosis

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


able to cause disease in plants


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

phytosanitary certificate

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


harmful to plants (usually used to describe chemicals)


parenchymatous tissue occupying the center of the stem


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

powdery mildew

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


(n. predisposition)
to make prone to infection and disease

primary inoculum

(syn. initial inoculum)
inoculum, usually from an overwintering source, that initiates disease in the field, as opposed to inoculum that spreads disease during the season

propagative transmission

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

protectant fungicide

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


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


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


(pl. pupae; v. pupate)  
quiescent stage between the larva and the adult of certain insects


small blisterlike elevation of epidermis formed as spores emerge


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


spore (conidium) produced in a pycnidium


(pl. pycnidia)  
asexual, globose or flask-shaped fruiting body of certain imperfect fungi producing conidia


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


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


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

resting spore

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

ribonucleic acid

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


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


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


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

root exudates

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

root graft

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

root hair

threadlike, single-celled outgrowths from a root epidermal cell


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


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


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


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

sap transmission

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


(adj. saprophytic; syn. saprobe)
organism that obtains nourishment from non-living organic matter


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


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


(pl. sclerotia)  
a vegetative resting body of a fungus, composed of a compact mass of hyphae with or without host tissue, usually with a darkened rind


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

secondary infection

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

secondary inoculum

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

secondary organism

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


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

seed treatment

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


carried on or in a seed


(adj. senescent, n. senescence)
to decline, as with maturation, age, or disease stress


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


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

slime molds

(syn. Myxomycetes)  
saprophytic organisms that form vegetative amoeboid plasmodia and spores


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

soft rot

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

soil drench

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

soil inhabitant

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

soil invader

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

soil pasteurization

process used to free soil of selected harmful microorganisms using heat

soil sterilization

process used to free soil of all microorganisms


carried on or beneath the soil surface


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


(abbr. for species; pl. spp.)
a genus name followed by sp. means that the particular species is undetermined; spp. after a genus name means that several species are being referred to


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


sporangium-bearing body of a fungus


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


(pl. sporangia)
saclike fungal structure in which the entire contents are converted into an indefinite number of asexual spores


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


to produce spores


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


unable to reproduce sexually;
to be free of living microorganisms


(adj. sterilized)
the total destruction of living organisms by various means, including heat, chemicals or irradiation


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


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


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

stylet knob

(syn. basal knob)  
structure at the base of a nematode stylet

stylet-borne transmission

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

sunscald or sunburn

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


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


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


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

systemic fungicide

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

temporary wilt

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


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

tissue culture

in vitro method of propagating healthy cells from plant tissues

tissue culture

in vitro method of propagating healthy cells from plant tissues


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


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


poisonous substance of biological origin


(n. transmission)
to spread or transfer, as in spreading an infectious pathogen from plant to plant or from one plant generation to another

trap crop

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


(syn. gall)
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


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


(also uredium; pl. uredinia)  
fruiting body (sorus) of rust fungi that produces urediniospores


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


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


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

vascular bundle

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

vascular wilt disease

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


a living organism (e.g., insect, mite, bird, higher animal, nematode, parasitic plant, human) able to carry and transmit a pathogen and disseminate disease;
(in genetic engineering) a vector or cloning vehicle is a self-replicating DNA molecule, such as a plasmid or virus, used to introduce a fragment of foreign DNA into a host cell


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

vegetative propagation

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


small vascular bundle in a leaf

vein banding

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

vein clearing

disappearance of green color in or around leaf veins


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


complete virus particle


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


degree or measure of pathogenicity; relative capacity to cause disease


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


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


self-set plant; plant seeded by chance


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

white rot

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

white rust

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


circular arrangement of like parts


drooping of leaves and stems from lack of water (inadequate water supply or excessive transpiration);
vascular disease that interrupts normal water uptake

wind break

a row or other grouping of trees or shrubs used to provide protection against the effects of high velocity winds


injuries to plant tissues that often breach barriers (cuticle, bark, cell walls) that might otherwise exclude pathogens; some pathogens (e.g. viruses) can enter plants only through a wound; wounds may occur from natural growth processes, physical and chemical agents, animals (especially insects), and many human agricultural activities, such as pruning


water and mineral conducting, food-storing, supporting tissue of a plant


unicellular ascomycetous fungus that reproduces asexually by budding


disease characterized by chlorosis and stunting of the host plant


an aggregate of the products resulting from growth or cultivation


targetlike development of tree canker, characterized by successive, perennial rings of callus; any symptom appearing in concentric rings


sporangium, or spore case, that bears zoospores


fungal spore with flagella, capable of locomotion in water