A
Acervulus (pl. Acervuli) - A saucer-shaped,
spore-
producing body of a fungus embedded in host tissue.
Actinomycetes - Filamentous bacteria that produce
several antibiotics and give soil its earthy smell.
Alternate Host - One of two kinds of plants on which a
parasitic fungus (e.g., rust) must develop to complete its life cycle.
Anthracnose - Disease caused by acervuli-forming fungi
(order Melanconzales) and characterized by
sunken lesions
and necrosis.
Antibiotic - A complex chemical substance produced by
one microorganism that inhibits or kills other
microorganisms (e.g.,
streptomycin).
Antibody - A specific protein formed in the blood of
warm blooded animals in response to the injection
of an antigen.
Antigen - Any foreign chemical (normally a protein) that
induces antibody formation in animals.
Antiseptic - A substance that prevents, retards, or
destroys microorganisms.
Apothecium - An open,
cuplike, or saucer-shaped
sexual fungal fruiting body containing asci.
Ascomycetes - A group of fungi characterized by the
production of sexual spores within an oval or tubular membranous sac
called an ascus.
Asci - Several saclike cells in which meiosis occurs
and
which generally contain eight spores each.
Asexual - Vegetative; without sex organs, sex cells, or
sexual spores, as the anamorph of a fungus.
Atrophy - The reduction in size of an organ by
distributed metabolism.
Autoecious - The need of only one host for completing
the life cycle of a rust.
B
Bacterium (pl. Bacteria ) - Microscopic one-celled
organism. Cell type lacks a distinct nucleus, sexual
recombination, and
chlorophyll. It does have cell walls and DNA.
Bactericide - Any chemical or physical agent that kills
or protects plants from bacteria.
Basidiomycetes - A group of fungi characterized by the
production of sexual spores on a club-shaped filament called the basidium.
Basidiospore - A haploid spore formed externally on a basidium.
Basidium (pl. Basidia; adj. Basidial) - Short,
club-
shaped fungus cell on which basidiospores are produced.
Blight - Any sudden, severe, and extensive spotting,
discoloration, or destruction of leaves, flowers, stems,
or entire
plants, usually attacking young, growing tissues. (In disease names,
often coupled with the name of the affected part
of the host; e.g., leaf blight, blossom blight, shoot blight).
Blotch - A blot or spot, usually superficial and
irregular
in shape and size, on leaves, shoots and fruit.
Burn - The condition in which the cells of the host become reddish or dark brown and collapse.
C
Callus - Parenchyma tissue that grows over a wound or
graft and protects it against drying or other injury.
Calyx - Outermost whorl of organs of a flower.
Canker - A dead area on a stem surrounded by living
cortical tissues.
Carrier - A plant or animal that carries a virus or
other infective agent without showing symptoms.
Chemotherapy - Treatment of disease by chemicals
(chemotherapeutants) working internally. Chemical agent has toxic effect
directly or indirectly on the
pathogens without injury to the host plant.
Chimera - A plant with several tissue sectors or layers
differing in genetic or chromosomal constitution from the
original plant.
Chlamydospore - A thick-walled asexual resting spore
formed by the modification of a fungus hypha.
Chlorosis - The abnormal plant color of yellowish-white
or gray condition of plant parts resulting from the
incomplete
destruction of the chlorophyll.
Cirrus (pl. Cirri) - A curllike tuft; a tendrillike mass
or
"spore horn" of forced-out spores.
Cleistothecium (pl.
Cleistothecia) - Closed, usually
spherical, ascus-containing structure of powdery
mildew fungi. A sexual
fruiting structure.
Conidiophore - The specialized fungal hyphal branch
that
bears the conidium.
Conidium (pl. Conidia) - Asexual spore formed by
abstriction and detachment of part of a hyphal cell at the end of a conidiophore and germinating by a germ
tube.
Coremium - A cluster of erect fungus filaments (hyphae)
that are joined together to form a column and that bear asexual spores
(conidia).
Cultivar (abbr. cv.) - A cultivated plant variety or
cultural selection. Used synonymously with variety.
Curl - The distortion, fluting, and puffing of a leaf
resulting from the unequal development of its two sides.
D
Damping-off - Decay of seeds in the soil or young
seedlings before or after emergence.
Diagnostic - Distinctive. A distinguishing
characteristic
serving to identify or determine the presence of a
disease
or other condition.
Dieback - Progressive death of shoots, branches, and
roots generally starting at the tips.
Diploid - Having a double set of chromosomes
(2n chromosomes) per cell.
Disease - The sum of the deviations of the vital
functions beyond the latitude of health. (This is just one of many
definitions of disease.)
Disinfectant - Any agent for destroying the causal agent
of disease after infection.
Disinfestant - Any agent that removes, kills, or
inactivates disease-causing organisms before they can cause
infection.
Dissemination - The spread of infectious material
(inoculum) from a diseased to a healthy plant by wind, water, humans,
insects, animal, machinery, or other means.
Dormancy - Non growing (inactive, quiescent) state of a
plant.
Dwarfing - The underdevelopment of any organ of a plant.
E
Enation - Epidermal outgrowth.
Endogenous - Produced inside.
Endophytic - Living within another plant.
Enphytotic - Plant disease that causes about the same
amount of injury each year.
Epidemiology (adj. Epidemiologic) - The study of
factors
influencing the initiation, development, and
spread of infectious disease.
Epinasty - An abnormal downward-curving growth or
movement of a leaf, leaf part, or stem.
Epiphytotic - The widespread and destructive
development
of a disease on many plants in a
community or communities.
Eradicant - Chemical used to eliminate a pathogen from a
host or an environment.
Eradication - Control of disease by eliminating the
pathogen after it is already established.
Escape - Plants in a given population that remain free
of disease where it is prevalent, although they possess
no natural
inherent resistance to the disease. (See
Klendusity.)
Etiolation - Yellowing and long, spindly growth as a
result of insufficient light.
Etiology - The description of the cause of disease.
Exclusion - Control of disease by preventing its
introduction (e.g., by quarantines) into disease-free
areas.
Exogenous - Produced outside.
Exudate - A substance (usually liquid) formed inside
a
plant and discharged from diseased or injured tissue.
The presence of an exudate often aids in diagnosis
(e.g., fire blight bacteria).
F
Facultative Parasite - An organism that is ordinarily
saprophytic but under proper conditions may be parasitic.
Facultative Saprophyte - An organism that is ordinarily
parasitic but under proper conditions may be saprophytic.
Fasciation - A distortion of a plant caused by an injury
or infection that results in thin, flattened, and sometimes
curved shoots.
Flagellum - A long hairlike or whiplike contractile
filament protruding from certain bacterial cells and spores of fungi and
that enable movement.
Flagging - The loss of turgor and the drooping of plant
parts, usually following a water deficit.
Fleck - A small, white to translucent lesion (spot)
visible
through a leaf.
Frass - Excrement of an insect, usually mixed with plant
debris.
Fruiting Body - Any of various complex, spore-bearing
fungal structures.
Fumigant - Vapor-active chemical used in the gaseous
phase to kill or inhibit the growth of microorganisms or
other pests.
Fungi Imperfecti - A major group of fungi for which no
sexual production of spores is known.
Fungicide - An agent that inhibits or kills fungi.
Fungistat - A chemical or physical agent that prevents
fungi from developing but does not kill them.
Fungus - A single- or many-celled, naked or covered,
irregular or filamentous organism, usually with a chitinous cell wall.
Lacking chlorophyll and incapable of manufacturing its own food, it feeds
on dead or living plant or animal matter.
G
Gall - Outgrowth or swelling of unorganized plant
cells
produced as a result of attack by bacteria, fungi, or
other organisms.
Germinate - To begin growth of a seed or spore.
Girdle - To circle and cut through; to destroy vascular
tissue, as in a canker or knife cut that encircles the stem.
Giant Cells - Large, usually multinucleate cells formed
by abnormal cell fusions or failure of proper cell wall
formation
following growth and nuclear division.
Associated with nematode feeding.
Gram-negative (alternatively,
Gram-positive) - A negative (or positive) reaction to
the standard Gram's stain for bacteria.
H
Haploid - The chromosome number of the gametophytic
generation or phase or having a single complete set of chromosomes.
Haustorium (pl. Haustoria) - A modified mycelial branch
that grows into a plant cell, makes intimate contact with the protoplast,
and absorbs food.
Heteroecious - Requiring two or more unrelated hosts for
completing the life cycle of a rust.
Heterothallic - Producing fusing gametes on separate and
distinct mycelia.
Homothalic - Producing fusing gametes on the same mycelium.
Host - The plant on or in which a parasite lives and
from which it obtains its food.
Hyaline - Clear, translucent.
Hyperplasia - The abnormal increase in the number of
cells without their enlargement.
Hypertrophy - The abnormal increase in the
size of cells, causing abnormal development of an organ or
tissue.
Hypha - A single filament of a fungus mycelium.
Hypoplasia - The underdevelopment of cells, tissues, or
organs.
I
Immunity - A relationship between a plant and a causal
agent in which the plant does not become diseased.
Incubation Period - Time between infection by a pathogen
and appearance of symptoms.
Indexing - Determining presence of disease in a plant by
removing buds or other parts for inoculation of a susceptible indicator
plant that exhibits specific
symptoms of a transmissible disease.
Infection - Process in which a pathogen enters, invades,
or penetrates and establishes a parasitic
relationship with a host plant.
Infestation - Presence in numbers (e.g., of insects,
mites, or nematodes). Do not confuse with "infection,"
a term that
applies only to living, diseased plants or animals.
Inoculum - Pathogen or pathogen part (e.g., spores,
mycelium) that infects plants.
Intercellular - Between the cells.
Intracellular - Within the cells.
K
Klendusity - Ability of an otherwise susceptible variety
of plant to escape infection because of the way it grows (e.g.,
early-maturing plants escape late-season diseases).
L
Latent - Present but not manifest or visible, as a symptomless infection.
Lesion - A local injury or delimited diseased area.
Local Necrosis - The death or disintegration of cells
and tissues in a localized area of an organ.
M
Macroscopic - Visible to the naked eye, without the aid
of a microscope.
Micron - A millionth of a meter (or, a thousandth of a
millimeter).
Microscopic - Visible only with the aid of magnification.
Monotrichous - Having only one flagellum.
Mosaic - Disease symptom characterized by nonuniform
foliage coloration, with a more or less
distinct intermingling of normal
and light green or
yellowish patches. Usually caused by a virus.
Mottle - An irregular pattern of light and dark
areas.
Mummification - The drying up and shriveling of fruits
and other plant parts.
Mummy - A dried and shriveled fruit.
Mushroom - A conspicuous fleshy fungus fruiting body.
Mycelium (pl. Mycelia) - The mass of interwoven
threads
(hyphae) making up the vegetative body
of a fungus.
Mycoplasma - Degenerate bacteria that do not have cell
walls. Mycoplasmas are smaller than bacteria but larger than viruses.
They cause animal and human diseases.
Mycoplasmalike Organism (abbr. MLO) - See Phytoplasma.
Mycorrhiza (pl. Mycorrhizae) - A symbiotic assocation of
a fungus with the roots of a plant.
N
Necrosis (adj. Necrotic) - The death or
disintegration
of cells and tissues.
Nematicide - A chemical or physical agent that kills,
inhibits, or protects against nematodes.
Nematodes - Generally microscopic tubular worms, usually
living free in moist soil, water, and decaying matter, or as parasites of
plants and animals.
O
Obligate - Necessary; obliged. An obligate parasite is
an organism that can live only on living tissue.
Oogonium (pl. Oogonia) - Female egg cell of oomycete fungi.
Oomycete - A group of fungi that produce oospores such
as Pythium, Phytophthora, and
Aphanomyces.
Oospore - Thick-walled, sexually-derived resting spore
of oomycete fungi.
Overwinter - To survive over the winter period.
P
Parasite - An organism that lives within or upon another
living organism from which it derives nourishment and in which it may
cause various degrees of injury.
Parasitism - The phenomenon of the growth of one
organism, the parasite, at the expense of another, the host.
Pathogen - An entity capable of producing disease.
Pathogenicity - An entity's capacity for producing a
disease.
Pectinase - The enzyme that breaks down pectic
substances to simple carbohydrates.
Perithecium - A round to flask-shaped, thick-walled
spore case containing asci and with an ostiole (pore).
Peritrichate (alt. Peritrichous) - Having flagella all
over the outside of the cell.
Pesticide - Any chemical or physical agent that destroys
pests (e.g., fungicide, insecticide, miticide).
Phycomycetes - A group of fungi that may consist ofone
cell or have filaments (hyphae) with few or no cross walls and that
reproduce sexually by union of two sex cells.
Phyllody - Change from a normal flower to leafy
structures. Characteristic of certain phytoplasma
infections.
Physiogenic Disease - A disease produced by some
unfavorable physical or environmental factors (e.g., light, temperature,
water, soil nutrients, chemical, physical or mechanical injury).
Phytoplasma - Microorganisms found in phloem
tissue that
resemble mycoplasmas in all respects
except that they cannot yet be grown
on artificial
nutrient media. Formerly known as mycoplasmalike
organism
(MLO).
Phytotoxic - Injurious to plants.
Plasmodium - A naked, multinucleate, vegetative
(fungal
) body capable of amoeboid motion.
Polymorphism - The existence of several asexual
spore
stages in the life cycle of an organism.
Primary Infection - The first infection of a plant,
usually in the spring by an overwintering sexual pathogen propagule.
Primary Inoculum - lnoculum, usually from an overwintering source, that initiates disease in the field, as opposed to inoculum that spreads disease during the season.
Propagule - The part of an organism that may be
spread
so as to reproduce the organism.
Protectant - A chemical applied to a plant surface in
advance of the pathogen to prevent infection.
Pustule - A local elevation of the epidermis that may
rupture to expose the causal agent (e.g., rust, smut, white rust, etc.).
Pycnidium (pl. Pycnidia) - )-The asexual, globose or
flask-shaped fruiting body of fungi-producing conidia.
Q
Quarantine - Regulation forbidding sale or shipment of
plants or plant parts, usually to prevent disease, insect, nematode, or
weed invasion of an area.
R
Race - A strain of a pathogen characterized by the
limitation of its host range to certain species and varieties of plants.
Resistance - The sum of the qualities of the host and
causal agent that retard the activities of the causal agent.
Rhizoid - Intercellular thallus branch that absorbs food
and provides anchorage.
Rhizomorph - An aggregation of hyphae into a cordlike
or rootlike strand.
Rickettsia - A single-celled animal and human
disease
causing organism with a partial cell wall that has not been grown
in culture.
Ringspot - Symptom of a disease characterized by
yellowish or dead (necrotic) rings with green tissue inside them, as in
certain virus diseases.
Rogue (alt. Roguing) - To remove and destroy
undesired
individual plants from a planting on the basis of disease infection, not
being true-to-type, insect infestation, or other reason.
Rot - Softening, discoloration, and often
disintegration
of succulent plant tissue as a result of fungal or bacterial infection.
Rugose - Wrinkled.
Russet - Yellowish-brown or reddish-brown scar tissue on
the surface of fruit.
S
Sanitation - Destroying all infested and infected plant
parts during the season.
Saprophyte - An organism that derives its nourishment
from dead organic matter.
Scab - Crustlike disease lesion.
Sclerotium (pl. Sclerotia) - A small, compact, hardened
mass of hyphae that may bear fruiting bodies. Can help fungus survive
adverse environments.
Scorch - "Burning" of plant tissue from infection, lack
or excess of some nutrient, or weather conditions.
Secondary Infection - lnfection resulting from the
spread of infectious material produced after a primary infection.
Senesce (n. Senescence; adj. Senescent) - To decline
with maturity or age, often hastened by stress from environment or disease.
Shothole - Disease symptom characterized by the
dropping
out of small, round fragments of leaves, making them look as if riddled
by shot.
Sign - The manifestation of disease by the presence of
structures of the causal agent.
Soilborne - Refers to many fungi able to survive in the
soil as saprophytes. Also called "soil inhabitant."
Sorus (pl. Sori) - A compact aggregation of spores
and/or sporophores growing out to the surface of the host.
Spiroplasma - A single-celled, wall-less, spiral,
filamentous organism associated with corn stunt and citrus stubborn disease.
Sporangiophore - A sporangium-bearing hypha.
Sporangium (pl. Sporangia) - A fruiting body that
produces asexual spores within a more or less
spherical wall.
Spore - Reproductive body of fungi and other lower
plants, containing one or more cells; a bacterial cell modified to
survive an adverse environment.
Sporodochium (pl. Sporodochia) - A cushion-shaped
spore-producing body of a fungus.
Sporogenous - Capable of forming spores.
Sporulation - The process of producing spores.
Sterilant - Any agent or chemical that destroys all
living organisms in a substance such as soil.
Streak - An elongated lesion with irregular sides.
Stroma (pl. Stromata) - A compacted mass of hyphae
that
supports sexual fruiting bodies.
Stunt - A wide range of parasitic and nonparasitic agents.
Stunted - An unthrifty plant reduced in size and vigor
due to unfavorable environmental conditions.
Stylet - Slender, tubular mouthparts in plant-parasitic
nematodes or aphids.
Substrate - The substance or object on which an organism
lives and from which it gets nourishment.
Sun Scald - Plant tissues burned or scorched by too
much
sun exposure and other unfavorable conditions.
Susceptibility - The sum of the qualities of a plant and
causal agent that allows the development of the causal agent.
Symptoms - External or internal physical characteristics
of disease expressed by the host plant.
Systemic - Pertaining to a disease in which an infection
leads to general spread throughout the plant body. Also,
a chemical that
spreads internally through a plant.
T
Teliospore - Thick-walled resting spore produced by
some
fungi, notably rusts and smuts, that germinates to form a basidium.
Thallus - The vegetative body of the lower plant that
has not differentiated into stems and leaves.
Tolerance - Ability of the plant to endure the
development of the parasite without showing marked
symptoms of disease.
Tylosis (pl. Tyloses) - A bladderlike intrusion of the
protoplasm from a parenchymatous cell through a pit into the lumen of a
xylem cell.
V
Variety - One or more races of a pathogen that are
characterized by the limitation of their host range to a certain genus or
genera. Also, a group of closely related plants of common origin and
similar
characteristics within a species (se
e also Cultivar).
Vector - An agent, such as an insect, nematode, or
fungus, that may transmit a pathogen.
Vein-banding - Symptom of a virus disease in which
regions along the veins are darker green than the tissue between the veins.
Viroid - An infectious nucleic acid without a protein
coat that causes potato spindle tuber or chrysanthemum stunt.
Virulent - Strong ability to produce disease.
Viruliferous - Capable of transmitting a virus.
Virus - Submicroscopic, infectious agent, too small to
be seen with a compound microscope, that multiplies
only in living cells.
A virus consists of nucleic acid
surrounded by a protein coat.
W
Water-soaked - Describing plants or lesions that
appear
wet and dark and are usually sunken and
translucent.
Wilt - Lack of freshness and turgor and drooping of
leaves from lack of water; a vascular disease that interrupts the plant's
normal uptake and distribution of water.
Witches' Broom - Abnormal, brushlike development
of
many
weak shoots.
Y
Yellowing - The yellow color of plant parts resulting
from the excessive proportion of yellow pigments, in turn produced by the
underdevelopment or partial
destruction of the green pigments.
Yellows - A disease characterized by yellowing and
stunting of affected parts (caused by fungi, virus,
bacteria, or
deficiency of essential elements).
Z
Zoospore - Fungus spore with flagella, able to move in
water.
Zygospore - A fungal resting spore produced by the
fusion of equal gametes.
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