Plant Pathology terms Flashcards
abaxial
directed away from the stem of a plant; pertaining to the lower surface of a leaf (contrasts with adaxial)
abiotic
pertaining to the absence of life; abiotic diseases are not caused by living organisms (pathogens), but by chemical and physical factors. (see also noninfectious) (contrasts with biotic, infectious)
abscission
the shedding of leaves or other plant parts as the result of physical weakness in a specialized layer of cells (the abscission layer) that develops at the base of the structure
acute
pertaining to symptoms that develop suddenly (contrasts with chronic)
acute toxicity
the ability of a single dose of a compound to poison (contrasts with chronic toxicity)
adaxial
directed toward the stem of a plant; pertaining to the upper surface of a leaf (contrasts with abaxial)
adpressed
closely flattened down or pressed against a surface; appressed
agar
a gelatinlike material derived from algae and used to solidify liquid culture media; term also applied to the medium itself
aggressiveness
the relative ability of a plant pathogen to colonize and cause damage to plants (see also virulence)
allelopathy (adj. allelopathic)
the ability of one species to inhibit or prevent the growth of another species through the production of toxic substance(s
alternate host
one of two kinds of plant required by a heteroecious rust fungus to complete its life cycle; sometimes used as a general term for the aecial host, or for the economically less important host (see also: aecial host and telial host)
alternative host
a plant other than the main host that a parasite can colonize; alternative hosts are not required for completion of the developmental cycle of the parasite
alternation of generations
a reproductive cycle in which a haploid phase alternates with a diploid phase
ammonification
the conversion of organic matter during decay by bacteria, fungi, and some other organisms into ammonia and ultimately ammonium, NH4, which can be absorbed by plants
anastomosis
the fusion between branches of the same or different structures (e.g. hyphae) to make a network
annual
a plant that completes its life cycle and dies within one year (contrasts with biennial, perennial)
antagonism
a general term for interference between organisms that may include antibiosis or competition for nutrients or space; action of two or more pesticides that reduces the effectiveness of one or all (contrasts with synergism)
apex
the tip of a root or shoot, containing the apical meristem
appressed
closely flattened down or pressed against a surface; adpressed
arable
able to be cultivated for agriculture
aseptate
having no cross walls; lacking septa (see also nonseptate; coenocytic) (contrasts with septate)
autotroph
an organism that synthesizes its nutritive substances from inorganic molecules; e.g., plants capable of photosynthesis (contrasts with heterotroph)
auxin
a plant hormone (growth regulator) influencing growth through cell elongation
avirulence (avr) gene
a gene in a pathogen that causes the pathogen to elicit an incompatible (defense) response in a resistant host plant, and may enhance pathogen virulence in a susceptible host plant. The outcome of the interaction of an avirulence gene product with its corresponding plant resistance (R) gene product is usually a hypersensitive reaction
avirulent
unable to cause disease (see also nonpathogenic) (contrasts with virulent)
avoidance
a principle of plant disease control in which plants are grown at times or locations where the pathogen is inactive or not present
axenic
a culture in the absence of living bacteria or other organisms; pure culture
axillary bud
a bud that develops in the axil of a leaf (see also lateral bud)
biennial
a plant that produces seed and dies at the end of its second year of growth (contrasts with annual, perennial)
binary fission
a type of asexual reproduction in which two cells, usually of similar size and shape, are formed by the growth and division of one cell
binucleate
having two nuclei
bioassay
any test (assay) using a living organism
biocide
a compound toxic to all forms of life
biological control
the exploitation by humans of the natural competition, parasitism and/or antagonism of organisms for management of pests and pathogens (see also biocontrol)
biotic
relating to life, as disease caused by living organisms (see also infectious) (contrasts with abiotic, noninfectious)
biotroph
an organism that can live and multiply only on another living organism (see also obligate parasite) contrasts with necrotroph)
blight
a sudden, severe, and extensive spotting, discoloration, wilting, or destruction of leaves, flowers, stems, or entire plants
breaking
a disease symptom, usually caused by a virus, involving addition or loss of flower color to create a variegated pattern. (see also flower break)
breeding line
a plant strain used in a plant breeding program and usually containing one or more desirable agronomic or breeding characteristics
brown rot (of wood)
a wood decay resulting from selective removal of cellulose and hemicellulose, leaving a brown amorphous residue that usually cracks into cubical blocks and consists largely of slightly modified lignin (contrasts with white rot)
callose
an amorphous, hardened carbohydrate constituent of plant cell walls, commonly developing upon injury
callus
the specialized tissues that form over a wound or cut in a plant; cork cambium may form, and the cells produced will gradually seal the wound
canker
a plant disease characterized (in woody plants) by the death of cambium tissue and loss and/or malformation of bark, or (in non-woody plants) by the formation of sharply delineated, dry, necrotic, localized lesions on the stem; the term canker also may be used to refer to the lesion itself, particularly in woody plants
capsid
the protective layer of protein surrounding the nucleic acid core of a virus; the protein molecules which make up this layer (see also coat protein)
capsule
the gel-like material surrounding a bacterial cell
carpel
the ovule-bearing structure of a flower in angiosperm she ovule-bearing structure of a flower in angiosperm
causal agent
an organism or agent that incites and governs disease or injury
chasmothecium
the ascocarp of powdery mildew fungi; it has no natural opening at maturity, but opens by the rupturing of its wall (see also cleistothecium)
chemotaxis
the movement or growth of an organism in response to changing concentration of a chemical stimulus, often in relation to food or for mating; chemotropism
chemotherapy
a treatment of plant disease with chemicals (e.g. antibiotics or fungicides) absorbed and translocated internally
chitin
the complex polysaccharide carbohydrate in fungal cell walls, animal exoskeletons, and nematode egg shells
chlamydospore
a 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
chloroplast
a disklike organelle containing chlorophyll in which photosynthesis occurs in the cells of green plants
chlorosis
the failure of chlorophyll development, caused by disease or a nutritional disturbance; fading of green plant color to light green, yellow, or white
circulative transmission
a type of virus transmission characterized by a long period of acquisition of the virus by a vector (typically an insect), a latent period of several hours before the vector is able to transmit the virus, and retention of the virus by the vector for a long period, usually several days; the virus circulates in the body of the vector (see also persistant transmission, propagative transmission) (contrasts with nonpersistant transmision, stylet-borne transmission)
coat protein
the protective layer of protein surrounding the nucleic acid core of a virus; the protein molecules which make up this layer (see also capsid)
coccus
a spherical (or near-spherical) bacterial cell
colonization
the establishment and ramification of a pathogen within a host plant
colonize
to infect and ramify through plant tissue with the growth of a pathogen
compartmentalization
the isolation of a specific tissue area by host barrier tissues
complete resistance
a resistant reaction in which some aspect of disease development, usually symptom expression or pathogen reproduction, is completely stopped (contrasts with partial resistance)
conjugation
the temporary contact of bacterial cells during which genetic material is transferred
contact fungicide
a fungicide that remains on the surface where it is applied and prevents infection often through the inhibition of spore germination; no after-infection activity (see also protectant fungicide) (contrasts with systemic fungicide)
continuous cropping
growing the same crop in the same location repeatedly
cotyledon
a seed leaf, one in moncots and two in dicots; primary embryonic leaf within the seed in which nutrients for the new plant are stored
crop rotation
the successive planting of different crop species; often used to improve soil fertility or to reduce disease and pest problems
cross-fertilization
a process in which sexual reproduction occurs as a result of the fusion of sex cells from different individuals (contrasts with self-fertilization)
cross-pollination
the transfer of pollen from the anthers of a flower on one plant to the stigma of a flower on another plant (contrasts with self-pollination)
cross-protection
the process by which a normally susceptible host is infected with a less virulent pathogen (usually a virus) and thereby becomes resistant to infection by a second, usually related, more virulent pathogen
cultivar
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) (see also variety)
cultural practices
the manner in which plants are grown, such as: application of nutrients, irrigation practices, type of cultivation; may be used for disease management
culture
the growth and propagation of microorganisms on nutrient media; growth and propagation of living plants
cuticle
the noncellular outer layer of an insect or a nematode; water-repellent, waxy layer of epidermal cells of plant parts, such as leaves, stems and fruit
cv. (abbr. for cultivar)
a plant type within a species, resulting from deliberate manipulation, which has recognizable characteristics (color, shape of flowers, fruits, seeds and height or form) (see also variety)
cytokinin
a plant hormones (growth regulator) that controls cell division and is important for shoot stimulation of callus in tissue culture
cytoplasmic inheritance
the inheritance of genes not located in the nucleus, i.e. those in mitochondria and chloroplasts (see also extrachromosomal inheritance, maternal inheritance)
damping-off
the 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
decoy crop
a crop that stimulates germination of seeds of a parasitic plant such as witchweed (Striga spp.), but is not susceptible to infection by the parasitic plant; helps reduce seed populations of the parasite in soil so a susceptible crop can be planted
desiccate
to dry out
determinate
ceasing vegetative growth when the first flower or reproductive structure forms
diagnostic (n. diagnosis)
pertaining to a distinguishing characteristic important for the identification of a disease or other condition
diapause
a period of spontaneous dormancy, independent of environmental conditions, interrupting developmental activity in an embryo, larva or pupa
dichotomous
branching, often successively, into two more or less equal arms
dicot or dicotyledon
a plant with two cotyledons or seed leaves (contrasts with monocot)
differential host
a plant host that on the basis of disease symptoms serves to distinguish between various strains or races of a given plant pathogen; differential cultivar
differential medium
a culture medium that is used to distinguish between organisms that can grow on it
differentiation
the physiological and morphological changes that occur in a cell, tissue, or organ during development from a juvenile state to a mature state
digitate
having lobes radiating from a common centre
dilution plating
a method to obtain pure colonies of bacteria and fungi in which infected plant material or infested soil is diluted in sterilized water. Small samples of the water are spread on the medium surface of several petri plates to find which dilution will produce pure colonies.
dilution streaking
the repeated streaking of bacteria on the surface of a nutrient medium with a sterile metal loop to allow pure colonies to grow
dioecious
having male and female organs on separate and distinct individuals (used primarily for plants) (contrasts with monoecious)
direct penetration
the penetration of plant tissues by a pathogen through a barrier such as leaf cuticle by chemical and physical means (e.g., infection peg, penetration peg) (contrasts with indirect penetration)
disease
the abnormal functioning of an organism
disease cycle
the succession of all of events and interactions among the host, parasite and environment that occur in a disease, from initial infection of the plant by a causal agent, through pathogenesis, to over-seasoning, until another infection occurs
disease incidence
the number of plants affected by a disease within a population
disinfect
to eliminate a pathogen from infected plant tissues
disinfest
to kill pathogens that have not yet initiated disease, or other contaminating microoganisms, that occur in or on inanimate objects as such soil or tools, or that occur on the surface of plant parts such as seed
dispersal or dissemination
the spread of infectious material (inoculum) from diseased plants to healthy plants
dormancy (adj. dormant)
a condition of suspended growth and reduced metabolism of an organism, generally induced by internal factors or environmental conditions as a mechanism of survival
downy mildew
a plant disease in which the pathogen appears as a downy growth on the host surface; caused by a member of the Oomycota (the oomycetes)
drift (of pesticides)
the movement of airborne particles of a spray, dust, or vapor away from the target area during or shortly after an application
durable resistance
a resistance that remains effective during prolonged and widespread use in an environment favorable to disease (see also horizontal resistance, race-nonspecific resistance) (contrasts with specific resistance, vertical resistance)
dwarfing
the underdevelopment of a plant or plant organs, which may be caused by disease, inadequate nutrition, or unfavorable environmental condition
ectoparasite
a parasite that feeds from the exterior of its host (contrasts with endoparasite)
ectotrophic
fungal development primarily over the root surface
effector
a pathogen molecule, usually a protein, that is translocated into host cells where it may act to directly manipulate host innate immunity
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
endemic
native to a particular place; pertaining to a low and steady level of natural disease occurrence
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
enzyme
a protein that catalyzes a specific biochemical reaction
epidemic
an increase of disease in a population; a general and serious outbreak of disease (see also epiphytotic)
epidermis (adj. epidermal)
the surface layer of cells of leaves and other plant parts
epiphytic
living on the surface of plants, 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
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
exclusion
the management of disease by excluding the pathogen or infected plant material from crop production areas (e.g., by quarantines and embargoes)
exudate
a liquid 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 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
fallow
cultivated land kept free from a crop or weeds during the normal growing season
fermentation
the oxidation of certain organic substances in the absence of molecular oxygen
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
foliar
pertaining to leaves
free water
unbound water; often used to describe a film of water on a plant surface
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
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)
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)
gibberellin
a plant growth regulator (hormone) that affects stem elongation
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
green manure
a crop plowed under while still green and growing to improve the soil; sometimes used to enhance populations of antagonistic microorganisms for biological control
growth regulator
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
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)
heterotroph
an organism that obtains nourishment from outside sources and must obtain its carbon from organic carbon compounds (contrasts with autotroph)
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)
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 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
hypovirulence
the reduced ability to cause disease
icosahedral (n. icosahedron)
having 20 faces, as a polyhedral virus particle (see also isometric)
immune
cannot be infected by a given pathogen
immunoassay
a detection method based on antibodies specifically selected to react with the substance to be detected (the antigen)
immunosuppressant
a chemical or activity that suppresses the natural immune responses in animals, including humans
in planta
in a plant
in situ
in its original place or environment
in vitro
in glass, on artificial media, or in an artificial environment; outside the host
in vivo
within a living organism
inclusion body
a structure developed within a plant cell as a result of infection by a virus, often useful in identifying the virus
incomplete dominance
the interaction of alleles of a gene that produces an intermediate phenotype, as in the production of pink flowers when red and white alleles are present in a heterozygous individual
incubation period
the time between penetration of a host by a pathogen and the first appearance of disease symptoms; the time during which microorganisms inoculated onto a medium are allowed to grow
indeterminate
continuing to grow vegetatively while producing flowers or reproductive structures (contrasts with determinate)
indexing
testing of a plant for infection, often by mechanical transmission or by grafting tissue from it to an indicator plant
indicator plant
a plant that reacts to a pathogen or an environmental factor with specific symptoms and is used to detect or identify the pathogen or determine the effects of the environmental factor
indirect penetration
the penetration of plant tissues by a pathogen through natural openings (e.g., stomata) or wounds (contrasts with direct penetration)
induced
produced in response to a stimulus (contrasts with constitutive)
induced systemic resistance (acronym ISR)
the reduced disease symptoms on a portion of a plant distant from the area where the inducing agent is active, caused by the triggering of active plant defenses against a variety of pathogens; used to describe increased resistance in plants induced by certain rhizobacteria (see also systemic acquired resistance, acronymn SAR
infect (n. infection)
to enter, invade, or penetrate and establish a parasitic relationship with a host plant
infection court
a site in or on a host plant where infection can occur
infection cushion
an organized mass of hyphae formed on the surface of a plant from which numerous infective hyphae develop
infection focus
an initial site of infection, followed by secondary spread, generally with reference to a population of plants
infection peg
the specialized, narrow hyphal strand on the underside of an appressorium that penetrates host cells (see also penetration peg)
infection period
the time required for infection to occur under conducive environmental conditions (usually hours of leaf wetness and temperature for foliar pathogens)
infectious
pertaining to a disease that is caused by a biotic agent capable of spreading from plant to plant (see also biotic) (contrasts with abiotic, noninfectious)
infective
referring to an organism able to attack a host and cause infection; referring to a vector carrying or containing a pathogen and able to transfer it to a host plant
initial inoculum
the inoculum, usually from an overwintering source, that initiates disease in the field, as opposed to inoculum that spreads disease during the season (see also primary inoculum) (contrasts with secondary inoculum)
inoculate (n. inoculation)
to place inoculum in an infection court; to insert a pathogen into healthy tissue
inoculum (pl. inocula)
a pathogen or its parts, capable of causing infection when transferred to a favourable location
inoculum density
a measure of the number of propagules of a pathogenic organism per unit area or volume
intercrop
to grow two or more crops simultaneously on the same area of land
isolate
(n. ) a culture or subpopulation of a microorganism separated from its parent population and maintained in some sort of controlled circumstance;
(v. ) to remove from soil or host material and grow in pure culture
karyogamy
the fusion of nuclei
Koch’s postulates
the procedure used to prove the pathogenicity of an organism, i.e., its role as the causal agent of a disease
lamina
the expanded part of a leaf (contrasts with petiole)
land race
a plant stock selected by farmers on a local basis over many years
latent
present but not manifested or visible, e.g., a symptomless infection by a pathogen
latent infection
an 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
lateral bud
a bud that develops in the axil of a leaf (see also axillary bud)
LD50 (abbrev. for lethal dose 50%)
a measure of relative acute toxicity; the dose of a compound that causes death in 50% of the test population treated
leaf dip
the inspection of a sample of sap from a suspected virus-infected leaf using an electron microscope
leaf spot
a plant disease lesion typically restricted in development in the leaf after reaching a characteristic size
leafroll
a disease symptom in which the edges of the leaf roll or turn, either up or down; often a symptom of virus infection
lesion
a localized diseased area or wound
ligase
an enzyme that catalyzes a reaction in which two molecules are linked together, such as linking cut pieces of DNA
lignification
the hardening of tissue through the deposition of lignin in the cell wall
lignin
a complex organic substance or group of substances that impregnate the cell walls of xylem vessels and certain other plant cells; a major constituent of wood
local lesion
a small, restricted lesion, often the characteristic reaction of differential cultivars to specific pathogens, especially in response to mechanical inoculation with a virus
macronutrient
an element needed in relatively large quantities for plant growth, e.g., nitrogen (N), phosphorus (P), and potassium (K); (contrasts with micronutrient)
MAMPS (acronym for microbe-associated molecular patterns)
the molecular signals or elicitors from microbes, including pathogens, that are recognized by plant or animal receptors andt can influence innate immunity of the host (see also pathogen-associated molecular patterns, acronym PAMPS)
marker-assisted selection
a procedure used in plant breeding in which genetic markers that are (a) easy to identify and (b) linked to desirable genetic traits that are difficult to identify (such as disease resistance) are used to aid in selection from a population
maternal inheritance
the inheritance of nonnuclear genes, i.e., those in mitochondria and chloroplasts (see also cytoplasmic inheritance, extrachromosomal inheritance)
mating types
the two compatible strains, usually designated + and - or A and B, necessary for sexual reproduction in heterothallic fungi
mechanical injury
an injury of a plant part by abrasion, mutilation, or wounding
mechanical transmission
the spread or introduction of inoculum to an infection court (wounding) by human manipulation, accompanied by physical disruption of host tissues
melanin
a brown-black pigment; common in sclerotia and other survival structures
meristem (adj. meristematic)
a plant tissue characterized by frequent cell division, producing cells that become differentiated into specialized tissues
meristem culture
the aseptic in vitro culture of a plant or plant part from a portion of the meristem; a method used to produce pathogen-free plants
metabolite
any chemical participating or resulting from metabolism; a nutrient
microbe
an organism of such small size that it can only be seen as an individual organism with the aid of a microscope (see also microorganism)
microclimate
weather conditions on a small scale, e.g., at the surface of the plant or within a crop
middle lamella
the layer, consisting largely of pectic substances, between the walls of adjacent plant cells
mildew
a thin coating of mycelial growth and spores on the surfaces of infected plant parts
mode of action
the mechanism by which a pesticide, drug, or other biologically active chemical functions
mold
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 surfaces of plant tissues
monogenic
determined by a single gene (contrasts with polygenic)
monogenic resistance
a resistance conferred by a single gene (see also single gene resistance) (contrasts with multigenic resistance, oligogenic resistance, polygenic resistance)
monoxenic culture
a culture containing one species of organism growing in the presence of one other species of organis
mosaic
a disease symptom characterized by nonuniform coloration, with intermingled normal, light green and yellowish patches, usually caused by a virus (see also mottle)
motile
capable of self-propulsion by means of flagella, cilia, or amoeboid or swimming movement
movement protein
for viruses, a protein encoded by the pathogen that is required for spread within an infected plant
multigenic resistance
resistance conferred by several genes (see also polygenic resistance) (contrasts with monogenic resistance, oligogenic resistance, single gene resistance)
multiparticulate virus
a plant virus in which the genome is divided into more than one piece of nucleic acid encapsidated in more than one particle
multipartite virus
a plant virus in which the genome is divided into more than one piece of nucleic acid
mycoherbicide
a pathogenic fungus used as a biological control agent to manage weeds or other undesirable plants
mycoparasite
a fungus that attacks another fungus
mycovirus
a virus that infects fungi
necrosis (adj. necrotic)
the death of cells or tissue, usually accompanied by darkening to black or brown
necrotroph
a parasite that typically kills host cells and obtains its energy from them (contrasts with biotroph)
negative-sense RNA (-RNA)
the ribonucleic acid sequence complementary to the positive or plus sense sequence; not translated into protein (contrasts with positive-sense RNA)
node (adj. nodal)
an enlarged portion of a shoot at which leaves or buds arise
nonpathogenic
unable to cause disease (see also avirulent)
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 (see also stylet-borne transmission) (contrasts with circulative transmission, persistent transmission, propagative transmission)
no-till
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
obligate parasite
an organism that can grow only as a parasite in association with its host plant and cannot be grown in artificial culture media (see also biotroph) (contrasts with necrotroph)
occlusion
a block or plug that stops the flow of liquids (as in vessels)
oedema
a swelling or blistering on leaves and other plant parts under conditions of high moisture and restricted transpiration (see also edema, intumescence)
oligogenic resistance
a resistance conferred by a few genes (contrasts with monogenic resistance, multigenic resistance, polygenic resistance, single gene resistance)
overseason
to survive or persist from one planting season to the next
overwinter
to survive or persist through the winter period
palisade parenchyma
the tissue found beneath the upper epidermis of a leaf, composed of elongate, tubular cells arranged upright, in the manner of posts in a palisade fortification
PAMPS (acronym for pathogen-associated molecular patterns)
the molecular signals or elicitors from pathogens that are recognized by plant or animal receptors and can influence innate immunity of the host (see also with microbe-associated molecular patterns, acronym MAMPS)
pandemic
a widespread and destructive outbreak of disease occuring simultaneously in several countries
papilla
the localized wall thickenings on the inner surface of plant cell walls at sites penetrated by fungi
parenchyma (adj. parenchymatous)
the soft tissue of living plant cells with undifferentiated, thin, cellulose walls
partial resistance
a resistance in which disease develops more slowly, or to a lesser extent, on the host, but the host does become diseased (contrasts with complete resistance)
pathogenesis
the production and development of disease
pathogenesis-related (PR) proteins
the proteins, such as antimicrobial proteins and hydrolytic enzymes, that are synthesized in the early events of the plant defense response
pathotype
a subdivision of a pathogen species characterized by its pattern of virulence or avirulence to a series of differential host varieties
pathovar (abbr. pv.)
a subdivision of a plant-pathogenic bacterial species defined by host range; pathovar for bacteria is equivalent to forma specialis for fungi
pectin
a methylated polymer of galacturonic acid found in the middle lamella and the primary cell wall of plants; the jelly-forming substance found in fruit
penetration
the initial invasion of a host by a pathogen
penetration peg
the specialized, narrow hyphal strand on the underside of an appressorium that penetrates host cells (see also infection peg)
perennial
something that occurs year after year; a plant that survives for several to many years (contrasts with annual, biennial
persistent transmission
a type of virus transmission in which the virus is acquired and transmitted by the vector after a relatively long feeding time and remains transmissible for a prolonged period while in association with its vector (see also circulative transmission, propagative transmission) (contrasts with nonpersistent transmission, stylet-borne transmission)
phloem
the food-conducting, food-storing tissue in the vascular system of roots, stems, and leaves
phloem necrosis
the death of phloem cells, often visible, caused by infection by systemic phloem pathogens such as phytoplasmas, spiroplasmas, and viruses
phytopathogenic
able to cause disease in plants
plasmogamy
the fusion of two sex cells
polyclonal antibodies
a mixture of antibodies produced by different antibody-producing cells against more than one epitope of an antigen (contrasts with monoclonal antibodies)
polygenic resistance
a resistance conferred by several genes (see also multigenic resistance) (contrasts with monogenic resistance, oligogenic resistance, single gene resistance)
positive sense RNA (+RNA)
the RNA that can serve directly as messenger RNA (contrasts with negative sense RNA)
post-transcriptional gene silencing (acronym PTGS)
a mechanism for sequence-specific RNA degradation in plants, resulting in the turning off of a gene; used as a host plant defense against viruses by degrading viral RNAs created during replication
powdery mildew
a common name for a disease caused by a white, powdery, superficial ascomycetous fungus that is an obligate parasite
predispose (n. predisposition)
to make prone to infection and disease
primary leaf
the first true leaf that emerges on a plant following the cotyledons
propagative transmission
a type of 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 (see also circulative transmission, persistent transmission) (contrasts with nonpersistent transmission, stylet-borne transmission)
pv. (abbr. for pathovar)
a subdivision of a plant pathogenic bacterial species defined by host range; pathovar for bacteria is equivalent to forma specialis for fungi
pyramiding
the addition, through plant breeding or genetic engineering, of several resistance genes into a single plant cultivar
qualitative resistance
resistance reactions that can be placed in distinct categories, usually conferred by one or a few genes (contrasts with quantitative resistance)
quantitative resistance
resistance reactions that have no distinct classes but vary continuously from resistant to susceptible, the result of few to many genes, the individual effects of which may be small and difficult to detect (contrasts with qualitative resistance)
quarantine
the legislative control of the transport of plants or plant parts to prevent the spread of pests or pathogens
quiescent
dormant or inactive
quorum sensing
the ability of bacteria to interact with each other through a variety of mechanisms; allows a population of bacteria to behave more like a multicellular organism
race-nonspecific resistance
a resistance that is effective against all biotypes of the pathogen. (see also durable resistance, general resistance, horizontal resistance) (contrasts with specific resistance, vertical resistance)
resting spore
a spore, often thick-walled, that can remain alive in a dormant state for some time, later germinating and capable of initiating infection
RNA interference (acronym RNAi)
a process within living cells in which a double-stranded complementary RNA targets a specific messenger RNA for destruction, blocking the function of (silencing) the gene from which the mRNA was transcribed
rosette
a disease symptom characterized by short, bunchy growth habit due to shortened internodes and no comparable reduction in leaf size
rot
the softening, discoloration, and often disintegration of plant tissue as a result of fungal or bacterial infection
rust
a disease caused by a specialized group of the Basidiomycota (the basidiomycetes) that often produces spores of a rusty color
sap transmission
the transmission of pathogens, usually viruses, by rubbing sap from an infected plant onto a healthy plant to cause infection
saprobe (adj. saprobic)
an organism that obtains nourishment from nonliving organic matter (see also saprophyte, saprotroph)
SAR (acronym for systemic acquired resistance)
the reduced disease symptoms on a portion of a plant distant from the area where a hypersensitive response occurred or other stimulus was applied; a rapid and coordinated defense response against a variety of pathogens as a signal travels throughout the plant (see induced systemic resistance)
sclerenchyma (adj. sclerenchymatous)
a plant tissue made up of thick-walled nonliving cells
selective medium
a culture medium containing substances that specifically inhibit or prevent the growth of some species of microorganisms or promote the growth of some organisms over others
smut
a disease caused by a smut fungus (Ustilaginomycotina) in the Basidiomycota or the fungus itself; it is characterized by masses of dark brown or black, dusty to greasy teliospores that generally accumulate in black, powdery sori
soft rot
a softening, discoloration, and often disintegration of plant tissue as a result of fungal or bacterial infection
species
any one kind of life subordinate to a genus but above a race; a group of closely related individuals of the same ancestry, resembling one another in certain inherited characteristics of structure and behavior and relative stability in nature; the individuals of a species ordinarily interbreed freely and maintain themselves and their characteristics in nature
specific resistance
a resistance that is effective against some biotypes or races of the pathogen, but not others, usually inherited monogenically and expressed qualitatively. (see also vertical resistance) (contrasts with durable resistance, general resistance, horizontal resistance, race-nonspecific resistance)
spot
a symptom of disease characterized by a limited necrotic area, as on leaves, flowers, and stems
stem pitting
a disease symptom characterized by depressions on the stem
sterilization (adj. sterilized)
the total destruction of living organisms by various means, including heat, chemicals, or irradiation
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 (see also nonpersistent transmission) (contrasts with circulative transmission, persistent transmission, propagative transmission)
subgenomic RNA
a piece of viral RNA, shorter than the entire genome of the virus, found in cells infected by the virus and sometimes encapsidated
susceptible (n. susceptibility)
prone to develop disease when infected by a particular pathogen (contrasts with resistant)
symbiosis (adj. symbiotic; n. symbiont)
the living together of two different kinds of organisms that may, but does not necessarily, benefit each organism
symptom
an indication of disease by reaction of the host, e.g., canker, leaf spot, wilt (contrasts with sign)
synergism (adj. synergistic)
a greater-than-additive effect of interacting factors (contrasts with antagonism)
synnema (pl. synnemata)
compact or fused, generally upright conidiophores, with branches and spores forming a headlike structure (see also coremium)
systemic
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
temporary wilt
the wilting due to insufficient soil water from which a plant can recover when water is supplied
tillage
the process of turning or stirring the soil
trap crop
a crop planted around a field to protect the inner crop from diseases transmitted by aerial vectors; host crop of a parasitic plant, (e.g., witchweed, Striga spp.), that is planted to stimulate seed germination, and later sacrificed by plowing under before the parasitic plant produces new seeds
Tuber
an underground stem adapted for storage, typically produced at the end of a stolon
turgidity
a state of being rigid or swollen as a result of internal water pressure
vascular
pertaining to fluid-conducting (xylem and phloem) tissues in plants
vascular bundle
a strand of conductive tissue, usually composed of xylem and phloem (in leaves, small bundles are called veins)
vascular cambium
a cylinder of meristematic cells (lateral meristem) that produces secondary phloem to the outside and secondary xylem (wood) to the inside of a branch or trunk of a woody plant
vascular cylinder
the cylinder of vascular tissue in stems or roots (see also stele)
vascular wilt disease
a disease of the xylem that disrupts the normal uptake of water and minerals, resulting in wilting and yellowing of foliage
vector
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
vegetative
referring to somatic or asexual parts of a plant that are not involved in sexual reproduction
vegetative propagation
a form of asexual reproduction in plants in which cuttings, bulbs, tubers, and other vegetative plant parts are used to grow new plants
vein banding
a symptom of virus disease in which regions along veins are either darker green or distinctly more yellow than tissue between veins
virion
a complete virus particle
viroid
an infectious, nonencapsidated (naked) circular, single-stranded RNA
viroplasm
the cellular inclusions that are sites of synthesis of viral components and the assembly of virus particles
virulence
a degree or measure of pathogenicity; the relative capacity to cause disease
virulent
highly pathogenic; having the capacity to cause severe disease (contrasts with avirulent)
viruliferous
virus-laden, usually applied to insects or nematodes as vectors
virus
a submicroscopic, intracellular, obligate parasite consisting of a core of infectious nucleic acid (either RNA or DNA) usually surrounded by a protein coat
wilt
the drooping of leaves and stems from lack of water (i.e., inadequate water supply or excessive transpiration); a vascular disease that interrupts normal water uptake
xylem
the water- and mineral-conducting, food-storing, supporting tissue of a plant
yellows
a disease characterized by chlorosis and stunting of the host plant
yield
an aggregate of the products resulting from growth or cultivation
