Introductory Plant Pathology

Introductory Plant Pathology

Class 1

Expectations, Realities, Formats, and Evaluation

By the end of class today the student will;

1. Know that PLPT/BIOS 369 is an IS course and will be taught with those expectations on the part of both the faculty and the student.

2. Understand the schedule3. Know how to access the class web-page and become familiar with it4. Know that faculty and TA's are available, approachable, eager to interact both inside and

outside of classes.

Moving from "Competency" level to "Mastery" level learning requires additional time engaged with course material beyond what one would spend to become competent. This does not necessarily mean that one need to acquire additional new information or"memorize" more "facts" but rather one spends additional time processing and thinking about the course materials in ways not necessarily presented in a classroom setting. Materials on this page may not seem to directly refer to material for a specific class.

To support you efforts at Masterly Level learning, a red M appears next to the number in the reading column. This is a link to supplemental material to enhance your studies. You may or may not think these links to be what you might anticipate as supplemental but they are intended to get you to look and think about the material in a different and/or deeper way.

It, in your studies you find material you think your fellow students (and myself) could benefit from reading. I would be pleased to include them on one of the Masterly Learning Pages

Websites:

What is Plant Pathology? "One Foot in the Furrow:

Symptom

Abnormal plant growth or function due to a disease. A symptom is a reaction of the PLANT.

Sign

Pathogen parts or products seen on a host plant. A sign is the PATHOGEN itself.

Local symptom

Symptoms restricted to a particular part of the plant.

Systemic symptom

Symptoms distributed throughout the plant by internal movement.

Primary symptom

Direct changes to the tissues initially infected by the pathogen

Secondary symptom

Indirect or subsequent changes in tissues away from the site of initial infection

Abortion

The halt in development of an organ after partial differentiation.

Abscission

Premature drop of leaves, flowers or fruit resulting from the premature formation of the abscission meristem.

Anthocyanescence

A reddish or purplish coloration of leaves resulting from abnormal development of anthocyanin pigments.

Bark roughening

The formation of rough bark where smooth bark normally occurs.

Blasting

The failure to develop fruit.

Bleeding

Chronic sap flow from wounds or other lesions.

Blight

The sudden drying and browning of whole leaves, shoots or branches.

Blister

Large swollen patches on leaves, fruit, etc.

Bronzing

A coppery or bronze coloration of the leaves.

Brooming

The clustering of organs such as branches about some common point on the plant. Generally arises from development of adventitious buds.

Burl

A hard woody, often flattened, hemispherical outgrowth on a tree.

Burn

See Scorch.

Callus

Tissue overgrowth produced in response to injury or other irritation and which tends to cover a wound, canker, etc.

Canker

A sunken necrotic lesion beginning in the bark of branches, trunk, or roots and usually becoming deeper and wider by normal or accelerated secondary growth (callusing) of cambium, phellogen, and traumatic meristem. This deepening continues as the pathogen encroaches transversely into the cambium and wood as well as tangentially in the cambium region. A typically well-developed canker is a symptom complex exhibiting necrotic, atrophic and hypertrophic symptoms.

Cast

See Abscission.

Chlorosis

Yellowing of green tissue due to chlorophyll destruction or failure of chlorophyll formation.

Curl

Abnormal bending or curling of leaves or shoots due to localized overgrowth on one side or in certain tissues.

Damping-off

A symptom complex characterized by rapid dying, browning, and rotting of germinating seedlings. Shoots may be killed before before emergence, stems may be attacked in the root collar region causing shoots to fall over, roots may be destroyed, or cotyledons may be attacked.

Decay

See Rot.

Defoliation

Loss of leaves through abscission.

Dieback

The progressive drying, shrivelling, and browning of twigs or branches from the tips inward toward the trunk.

Drop

Premature abscission of fruit or twigs.

Dwarfing

Subnormal size of a plant or some of its organs.

Epinasty

A leaf curl in which the leaves turn downward, due to a more rapid growth of cells on the upper side than on the lower side of the leaf stalk.

Etiolation

A symptom complex in which the major symptoms are dwarfing of foliage and inflorescence, spindly stem growth, and chlorosis.

Exudate

See Ooze.

Fasciation

Flattening or cohering of organs such as stems, flowers, and roots. The cause is unknown, but in some cases the condition can be propagated.

Flagging

Loss of rigidity and drooping of leaves and young shoots preceding whole plant wilting.

Gall

A pronounced tumefaction, often more or less spherical and usually composed of undifferentiated cells.

Girdling

Tangential enlargement of a canker or lateral coalescence of cankers causing a branch or stem to be encircled and resulting in the complete stoppage of conduction.

Greening

See Virescence.

Gummosis

The formation of gums by diseased cells and tissues and the extrusion of gum from wounds and other lesions.

Hairy root

Abnormal number of fine fibrous roots frequently making compact clusters.

Heterotropy

The adventitious development of normal tissues or organs in unusual areas.

Hydrosis

A water soaked, translucent appearance of leaves, fruits and green stems due to the extrusion of water from the cells into the intercellular spaces.

Hyperplasia

An abnormal increase in number of cells in a particular tissue or organ.

Hypertrophy

An abnormal increase in the size of a plant or plant part generally due to an abnormal increase in the size of the cells.

Hypoplasia

An abnormally small number of cells in a particular tissue or organ.

Hypotrophy

An abnormally small plant part generally due to abnormally small cells.

Knot

A type of tumefaction.

Leaf retention

The abnormally long retention of leaves usually resulting from a failure to develop the abscission meristem.

Lesion

A localized area of diseased tissue.

Mosaic

Pale green mottling of leaves.

Mottle

An irregular pattern of indistinct light and dark areas.

Mummy

A dried shriveled fruit that is generally the result of a fungal disease.

Necrosis

The death and disintegration of cells and tissues.

Oozes

Viscid masses composed of living or dead pathogen structures and partially disintegrated host tissues.

Pitting

Superficial depressions in the surface of succulent organs resulting from the death and shrinkage of subepidermal cells.

Prolepsis

Premature development of a shoot from a bud.

Proliferation

Continued or extended development of a plant part beyond the point at which growth normally ceases.

Reddening

The loss of green color from chlorophyllous tissue due to the destruction of the chlorophyll and/or the degeneration of chloroplasts which unmasks red pigments. Reddening may also result from the production of decomposition products accompanying death and deterioration.

Resinosis

The flow of resin or pitch from wounds or other lesions in conifers.

Restoration

The development of tissues or organs that normally would be only rudimentary.

Rosetting

A shortening of internodes through failure to elongate, which results in a crowding of the foliage.

Roll

See Curl.

Rot

The disintegration and decomposition of dead tissues.

Russeting

Rough or corky surfaces formed where they do not normally occur.

Scab

A limited, more or less circular, raised, and sometimes roughened lesion on fruits, tubers, leaves, and stems resulting from an overgrowth of epidermal, cortical, and peridermal tissues. This overgrowth is usually accompanied by rupturing and suberization (corking of cell walls).

Scaling

The formation of scales or corky material where scales normally do not occur.

Scorch

A sudden drying and browning of large, indefinite areas on leaves and fruits. Also damage to bark resulting in drying and death.

Shelling

Large scale loss of leaves through premature abscission.

Shot-hole

Holes in leaves caused by the falling out of killed spots of tissue.

Silvering

A silvery sheen or gray luster of leaf or primary bark surfaces due to the development of unnatural air spaces beneath the epidermis

Spike top

Death of the entire crown of a tree causing a pattern that resembles staghead.

Spot

Circular, areolate, or irregular discolored and dead areas on leaves, fruits, or green stems.

Staghead

Dieback or flagging of entire large branches in the crown, or of the entire top of a tree.

Streak

Elongated, narrow, lesions which are first water soaked then brown, in foliage or green stems. In wood there is discoloration in axial streaks within the outer, conducting layer of sapwood resulting from deterioration of the wood structure or extraneous components.

Stripe

The streak symptom in monocots.

Stunting

A type of dwarfing in which the entire plant is subnormal in size.

Suppression

The complete prevention of organ development.

Tumor

Local swelling on any part of the plant, usually woody roots, stem, or branches, usually resulting from stimulation of the plant meristem by the pathogen.

Variegation (also breaking)

Loss of color in streaks in petals of flowers.

Virescence

The process in which a normally white or colored tissue develops chlorophyll and becomes green.

Wart

A horny, hardened protuberance.

Water Soaking

See Hydrosis.

Wilting

A flaccid appearance of leaves and shoots resulting from a temporary or permanent loss of turgor due to excess transpiration by the leaves and shoots.

Witches' broom

A type of overgrowth in which there is an abnormal bushlike development of many weak shoots or roots.

Yellowing

The loss of green color from chlorophyllous tissues, due to the destruction of the chlorophyll and/or degeneration of the chloroplasts, which unmasks yellow pigments.

Signs

Symptom


Sign


Bacterial streaming

Observation of bacteria and bacterial products streaming out of plant tissue and into water.

Ooze


Egg

Reproductive propagule of nematodes.

Egg Mass

A group of eggs produced in a gelatinous matrix by a nematode female.

Cyst

A female nematode body filled with eggs produced by some nematodes.

Hypha

Vegetative structure of fungi and Oomycetes.

Mycelium

A mass of hyphae.

Rhizomorph

Macroscopic rope-like strand of compacted tissue formed by certain fungi.

Sclerotia

Macroscopic mass of hyphae, usually rounded and darkened.

Stroma

Macroscopic mass of hyphae, usually flattened and containing fruiting structures.

Spore

Reproductive propagule of fungi and Oomycetes.

Sporocarp

Fungal fruiting body, any structure that produces spores.

Pustule

Small blister like elevation of epidermis created as spores form underneath and push outward.

Oomycetes

Hypha


Coenocytic hyphae

Hyphae without crosswalls, found in Oomycetes, some other protists and some fungi.

Oospore

Sexual spore produced by Oomycetes characterized by a thick cell wall, this is the resting or survival stage.

Oogonium

Female gamete of Oomycete that is fertilized by an antheridium to form an oospore.

Antheridium

Male gamete of Oomycete that fertilize an oogonium to form an oospore.

Sporangium

Non-motile asexual spore produced by Oomycetes, lemon or globulose in shape.

Sporangiophore

A specialized hyphae that produces sporangia.

Zoospore

A motile asexual spore characterized by two flagella. Found in Oomycetes and Plasmodiophoromycetes. Chytrids produce zoospores with a single flagellum.

Germ tube

The early growth of mycelium from a germinating spore.

Groups of Oomycetes you should know

Pythium - Important cause of damping off and root rots.

Phytophthora - Species in this genera cause late blight of potato, sudden oak death and other root rots, fruit rots, cankers and diebacks.

Aphanomyces - Important casue of damping off and root rots.

Downy mildew - A group of several genera of Oomycetes that cause foliar diseases on many different plant species, characterized by production of sporangiophores on the the lower surface of leaves.

Ascomycetes and Deuteromycetes

Septate

Having cross walls in a hypha or spore. A cross wall is called a septum.

Germ tube

The early growth of of a hypha produced by a germinating fungus spore.

Apressorium

The swollen tip of a hypha or germ tube that facilitates attachment and penetration of the host by a fungus.

Haustorium

A specialized fungal hyphae that enters and absorbs nutrients from a host cell.

Ascomycetes

Fungi in the Phylum Ascomycota that produce sexual spores in sac-like structures called asci.

Deuteromycetes

A group of fungi with no known sexual stage. Often, when a sexual stage is discovered, these fungi turn out to be Ascomycetes.

Anamorph

The imperfect or asexual stage of a fungus.

Teleomorph

The perfect or sexual stage of a fungus.

Conidia

Asexual, non-motile spores of fungi.

Conidiophore

A specialized hypha that produces conidia.

Ascocarp

Fruiting body of Ascomycetes that contain the asci and ascospores.

Asci

A sac-like structure that contains ascopores.

Ascospores

Sexual spores of Ascomycetes produced in an ascus.

Apothecia

An open cup-shaped ascocarp.

Perithecia

A flask-shaped ascocarp with an opening for releasing spores.

Cleistothecia

An ascocarp where the asci are completely enclosed.

Sporodochium

An asexual fruiting structure consisting of a cluster of conidiophores woven together on a mass of hyphae.

Pycnidium

A flask-shaped asexual fruiting body with an opening for releasing spores..

Acervulus

A subepidermal, saucer-shaped, asexual fruiting body producing conidia on short conidiophores.

Synnema

An asexual fruiting body consisting of fused conidiopores to form a stalk with conidia on the end.

Chlamydospores

A thick-walled asexual spore formed by the modification of a hyphal cell.

Sclerotia


Groups of Ascomycetes and Deuteromycetes to know

Taphrina - Species in this genus have naked asci and cause various leafg curl diseases.

Powdery Mildew - A group consisting of several genera of fungi that cause foliar diseases on many different plant species characterized by white surface mycelium, chains of condia (giving the leaf surface a powdery appearance) and production of cleistothecia.

Verticillium - Two species in this genus cause of Verticillium wilt, an important vascular wilt. The fungus has a wide host range and produces microsclerotia.

Colletotrichum - Species in this genus cause anthracnose diseases on many different plant hosts. Anthracnose diseases are characterized by blackened sunken leasions. Colletotrichum species produce acervuli.

Fusarium - Species in this genus (most commonly Fusarium oxysporum) cause Fusarium wilt of many different plant species. Fusarium oxysporum produces microconidia, macroconidia and chlamydospores.

Alternaria - Species in this genus cause lesions and blights on many different host species. Alternaria species produce dark, multicellular conidia in chains.

Septoria - Species in this genus cause lesions and blights on many different host species. Septoria species produce long, thin conidia in pycnidia.

Basidiomycetes

Basidiomycetes

Fungi in the Phylum Basidiomycota that produce sexual spores on a basidium.

Basidiocarp

Fruiting body of Basidiomycetes that contain the basidia and basidiospores.

Basidium

A club-shaped structure that prodcued basidiospores.

Basidiospores

Sexual spores of Basidiomycetes prodcued on basidia.

Dikaryotic hyphae

Hypahe with two haploid nuclei. This is the normal vegetative state for Basidiomycetes.

Clamp connections

Specialized hyphal structure that maintains the dikaryotic condition of Basidiomycete hyphae.

Telia

Rust and smut fruiting bodies that produce teliospores.

Teliospores

Overwintering spores of rusts and smuts that produce basidia and basidiospores.

Aecia

Rust fruiting bodies that produce aeciospores.

Aeciospores

Dikaryotic spore of a rust fungus produced in an aecium; in heteroecious rusts, a spore stage that infects the alternate host.

Spermatia

Male gametes of rust fungi.

Spermagonia

Rust fruiting bodies that contain receptive hyphae and produce spermatia.

Receptive hypha

The part of a rust fungus spermogonium that receives the nucleus of a spermatium.

Uredia

Rust fruiting bodies that prodcue uredospores.

Uredospores

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.

Macrocyclic

Rusts that produce all five spore types.

Microcyclic

Rusts that lack one or more of the five spore types.

Heteroecious

Rusts that require two different hosts to complete their life cycle.

Autoecious

Rusts that complete their life cycle on a single host.

Groups of Basidiomycetes to know

Rusts

Smuts

Wood rotting fungi

Rhizoctonia

Other fungi and fungal-like organisms

Myxomycetes

Slime molds - Fungal-like protists that can cause disease by growing on the surface of plants

Plasmodiophoromycetes

Fungal-like protist that cause a few important plant diseases. They produce resting spores and zoospores.

Zoospore


Resting spore

Long term survival spores produced by Plasmodiophoromycetes.

Chytridiomycota

Chytrids - True fungi that lack true mycelium. They produce resting spores and zoospores with a single flagellum.

Zygomycetes

Group of fungi with coenocytic hyphae that produce thick walled resting spores called zygospores and sporangiospores.

Zygosporangia

Thick-walled sexual spores produced by Zygomycetes.

Sporangiospores

Asexual spores produced in a sporangium by Zygomycetes.

Genera of other fungi and other fungal-like organisms to know

Physarum - Genus of slime mold causing disease on turf

Plasmodiophora - Genus of Plasmodiophoromycetes causing club root of cabbage

Spongospora -Genus of Plasmodiophoromycetes causing powdery scab of potato

Rhizopus - Genus of Zygomycetes that are oppotunistic pathogens casuing soft rots mainly on fruit

Nematodes

Nematodes

Nematoda - Phylum of worm-like animals. Soil dwelling and plant parastic nematodes are microscopic.

Stylet

A long, slender, hollow feeding strcuture used by plant parasitic nematodes.

Ectoparasite

A parasite that feeds from outside the host.

Endoparasite

A parasite that enter and feed from inside the host.

Sedentary

Describes a life style of plant parasitic nematodes that stay in one place and set up a feeding site.

Migratory

Describes a life style of plant parasitic nematodes that move through the host as they feed.

Egg


Egg Mass


Cyst


Juvenile

Immature, non-reproductive stage of nematodes.

Giant cells

Syncytial structure produced by Meloidogyne spp. as a feeding site.

Syncytia

A large, multinucleate, cell-like structure.

Groups/Genera of nematodes to know

Meloidogyne - Root knot nematodes, these sedentary endoparasites form galls on plant roots.

Heterodera and Globodera -Cyst nematodes, these sedentary endoparasites produce cysts on plant roots. Heterodera glycines - Soybean cyst nematode.

Pratylenchus - Lesion nematodes, these migratory endoparasites cause lesions on roots.

Viruses

Virus

A submicrscopic obligate parasite consisting of nucleic acid and protein.

Viroids

Small RNAs that can infect a host and cause disease

Nucleoprotein

Refering to viruses, which consist of nucleic acid and protein

Submicroscopic

Particles too small to be seen with a compound microscope

Multipartite/Multiparticulate

Refers to viruses which are packaged in multiple particles

Coat Protein

Protein, encoded by virus nucleic acid, which covers the viral nucleic acid

Inclusion body

Aggregation of virus partilces in a host cell that is visible with a compound microscope

Plasmodesmata

A connection across a plant cell wall that connects the cytoplasm of two neighboring cells

Movement Protein

Protien, encoded by virus nucleic acid, that facilitates the movement of the virus through the plant and/or by the vector

Vector transmission

Transmission of a pathogen from plant to plant by another organism

Mechanical transmission

Refers to virus transmission from plant to plant by infected plant sap

Non-persistant transmission

Refers to vector trasmission of a virus where the vector quickly picks up virus particles on its mouthparts and is infective for a short period of time (hours).

Semi-pertsistant transmission

Refers to vector trasmission of a virus where virus particles enter the vectors foregut. In this case the vector also picks up the virus quicly but is infective for somewhat longer (days) than with non-persistant transmission.

Circulative transmission

Refers to vector trasmission of a virus where virus particles must circulate through the vectors hemolymph and enter the salivary glands to be tramsitted. In this case the vector aquisition and retention time is longer than with non or semi-persistant transmission.

Propagative transmission

Refers to vector trasmission of a virus where virus particles are repliacted in the the vector. In this case the vector retention time is longer than with circulative transmission and, in some cases, the virus can be transovarially transmitted.

Transovarial transmission

Refers to viral transmission from an insect vector to its offspring, meaning offpring of an infected vector are also infective.

Aquisition period

Refers to the period of time need for a virus vector to aquire a virus while feeding on an infected plant host.

Inoculation period

Refers to the period of time need for a virus vector to transmit a virus while feeding on an uninfected plant host.

Latent period

Refers to the period of time before a vector is infective after picking up the virus from an infected host.

Hemolymph

Fluid of an insects circulatory system, "insect blood"

Viruses to know

Tobacco mosiac virus (TMV) - Highly stable, rod-shaped virus that is an important pathogen of tobacco and other solanaceous crops. It was the first virus to be discovered.

Cucumber mosiac virus (CMV) - Multipartite, isometric virus that is an important pathogen of many plants, most importantly cucumbers, melons, peppers, beans, bananas and brassicas.

Potato virus Y (PVY) - Flexuous rod-shaped virus that is an important pathogen of potato and other solanaceous crops.

Papaya ringspot virus (PRV) - Flexuous rod-shaped virus that is an important pathogen of papaya. It almost destroyed papaya production in Hawaii until a genetically engineered resistance was developed.

Tomato spotted wilt virus (TSWV) - Spherical virus with a membrane enclosing the nucleoprotien that is an important pathogen with a wide host range.

Bacteria

Bacteria

Large group of ubiquitous single celled prokaryotes.

Extracellular polysacharide

Substance produced and excreted by bacteria for protection and/or adherance. It is what gives bacterial colonies a "slimy" appearance when grown in culture.

Flagellum

A long whip-like structure used by bacteria for movement.

Pili

Hair-like appendage of found on the surface of a baterium. Used for conjugation with another bacterium.

Plasmid

Small, circullar, extrachromosomal DNA found in bacteria.

Gram positive

Refers to a group of bacteria with one membrane in association with their cell wall.

Gram negative

Refers to a group of bacteria with two membranes in association with their cell wall.

Fission

Refers to bacterial reproduction by simple cell division.

Quorum sensing

Dependence of bacterial behavior and pathogenicity on thier cells reaching a certain density by sensing the concentration of certain signal molecules.

Phage

Virus that attacks bacteria.

Transposons/Insertion elements

A segment of chromosmal DNA that can move around in the genome.

Natural transformation/competence

When a bacterial cell takes up DNA from the environment.

Ti-plasmid

Tumor inducing plasmid of Agrobacterium tumefaciens that causes gall formation and opine production by infected plants.

Opines

Nitrogen and sugar source used by Agrobacterium tumefaciens.

Type three secretion system

Protein sectretion system used by some bacteria to inject bacterial proteins into a host cell.

Stomates

Microscopic pores on plant leaves used for gas exchange.

Plant pathogenic bacterial genera and species to know

Pectobacterium and Dickeya spp. - Soft rot pathogens.

Agrobacterium tumefaciens - Causal agent of crown gall.

Pseudomonas syringae - Large group of plant pathogenic bacteria with more host specific pathovars that are important pathogens of many crops.

Ralstonia solanacearum - Causal agent of bacterial wilt.

Citrus greening disease - Important bacterial disease of citrus.

Erwinia amylovora - Causal agent of fire blight, an important disease of apple and pear.

Streptomyces spp. - Large group of common, antibiotic producing, filamentous bacteria. Streptomyces scabies causes common potato scab.

Parasitic plants

Plant parasitic plants

Vascular, flowering plants that get nutrients directly from the host plant. These plants have a close relatioship with the host plant. They have specialized structures (haustoria) to enter the host's vasuclar tissues and retrieve nutrients.

Haustoria

Specialized structure, a modified root, of a parasitic plant that enters the host host plant and obtains nutrients. (The same term is used for a specialized fungal hyphae that enters and absorbs nutrients from a host cell.)

Hemiparasites

Parasitic plants that have chlorphyl and can make some of their own sugar but still rely on thier host for water and other nutrients.

Holoparasites

Parasitic plants that do not have chlorphyl and rely on thier host for all nutrients.

Climbing vines

A group of plants that have roots and grow in the soil, but still damage other plants by growing over them and restricting photosynthesis and/or vascular systems.

Parasitic plant genera to know

Phoradendron spp. - Leafy mistletoe (genus found in the United States) is a semi-parasitic plant that parasitizes hardwoods.

Striga spp. - Witchweed is a semi-parasitic plant that parasitizes many crop species, mainly in Africa and Asia.

Cuscuta spp. - Dodder is a true parasite that parasitizes many crop species in many areas of the world.

Arceuthobium spp. - Dwarf mistletoe is a true parasite that parsitizes conifer trees.

Epidemiology

Epidemic

A disease increase in a population; usually a widespread and severe outbreak of disease.

Epidemiology

The study of factors affecting the outbreak and spread of disease.

Disease incidence

The number or poroportion of individuals that are diseased.

Disease severity

The amount or proportion of tissue that is diseased.

Disease progress curve

A graph that plots disease vs. time.

Polycyclic disease

A disease with several cycles each year (or growing season) of inoculum production and infection.

Monocycic disease

A disease where only one disease cycle is completed each year or growing season.

Primary inoculum

Inoculum that produces the first infection of plants in a year or growing season.

Secondary inoculum

Inoculum produced by previous infections that infect in the same year or growing season.

Inoculum density

The number of infective units in a given volume or area.

Disease-gradient curve

A graph that plots disease vs. distance from an inoculum source.

Diagnosis

Selective medium

Medium used to isolate a target organism, and no other organisms. These media are designed to enhance growth of the target organism while inhibiting growth of non-target organisms.

Differential medium

Medium that differentiates between the target organism and all others that may grow on that particular medium. Differentiation is often based on color.

Indicator plants

Certain plant species or cultivars that show characteristic symptoms of infection.

Differential hosts

Host range can be tested and compared to known pathogens for identification

Antibodies

A type of protien produced by vertebrate immune systems to detect harmful substances.

Antigens

Substances, ususally proteins, detected by antibodies.

ELISA

Enzyme linked immunosorbent assay - a test used to detect antigens. Antibodies can be created to detect pathogen proteins.

PCR

Polymerase chain reaction - technique to amplify sequences of DNA. Can be used to detect specific sequences of pathogen DNA.

DNA fingerprinting

Technique for pathogen identification where restirction enzymnes are used to cut genomic DNA, producing a pattern specific to a pathogen.

Plant Disease Management Strategies

Avoidance

Prevent disease by selecting a time of the year or a site where there is no inoculum or where the environment is not favorable for infection.

Exclusion

Prevent the introduction of inoculum.

Eradication

Eliminate, destroy, or inactivate the inoculum.

Protection

Prevent infection by means of a toxicant or some other barrier to infection.

Resistance

Utilize cultivars that are resistant to or tolerant of infection.

Therapy

Cure plants that are already infected.

Other terms related to disease management

Antagonism

The activity of any organims that suppresses the activity of a pest organism. An antagonist is not autmatically a biological control agent, but antagonists are used to create biological controls.

Crop rotation

Planting of different crops in the same area in sequential years (or seasons) to balance fertility and reduce the build up of crop pests.

Integrated Pest Management

The attempt to prevent pests from causing economic damage by using a variety of management methods that are cost effective and cause the least damage to the environment.

Host resistance

Interaction phenotype

The phenotypic reaction of a plant to an interaction with a potential pathogen at a given point in time and environment.

Susceptible

Phenotypic expression related to extensive symptom development and/or pathogen reproduction and accomplished by uninhibited invasion of host by pathogen.

Resistant

Phenotypic expression related to complete or partial suppression of symptom severity and/or pathogen reproduction and accomplished by arrested or slowed invasion of host by pathogen.

Partial resistance

Expression of symptoms, but less than full susceptibility or greater than complete resistance.

Non-host reaction

No interaction of pathogen and host; the pathogen is unable to infect the plant because the plant is not a host.

Hypersensitive response

Plant responds to pathogen infection by quickly killing the infected cells, blocking the advance of the pathogen.

Pathogenicity/Virulence

Refers to the ability of a microbe to cause disease (invade, infect, cause symptoms, reproduce).

Avirulence

Refers to the inability of a pathogen to cause disease.

Race

A genetically and often geographically distinct mating group within a species; also a group of pathogens that infect a given set of plant varieties.

Aggressiveness

Virulent forms of pathogen cause differing degrees of symptom severity.

Single gene resistance

Resistance attributed to the function of a single gene. Often confering complete resistance or hypersensitive response.

Polygenic resistance

Resistance attributed to the function of multiple genes. Often confering partial resistance.

Race specific resistance

Resistance that is effective against only one race of a pathogen and not other races of the same pathogen.

Rate-reducing resistance

Partial resistance where that pathogen is able to infect the plant but reproduction is reduced or eliminated thereby reducing the spread of the pathogen.

R gene

Resistance gene, a plant gene that confers resistance to a pathogen.

Avr gene

Avirulence gene, a pathogen gene whose product is recognized by a plant and leads to a resistant reaction in the plant.

Avr protein/effector

A pathogen protein that is recognized and leads to a resistant reaction in resistant plants but that is often a virulence factor in susceptible plants.

Systemic aquired resistance

Whole plant resistance response that occurs following an earlier localized exposure to a pathogen.

Transgenic plants

Plants that have been genetically manipulated to express a gene from a different species.

Chemical control

Preventative

Refers to a chemical control method aimed at preventing infection of the pathogen.

Curative

Refers to a chemical control method aimed at inhibiting the development of an established infection.

Protectant

Refers to a chemical meant to reside on the plant surface as a preventative control measure.

Systemic

Refers to a chemical meant to be taken up by and distributed throughout the plant as a preventative or curative control measure.

ED 50

Effective dose, the amount needed to have the desired effect in 50% of the population.

Active ingredient

In pesticides, the chemical responsible for the desired effect.

Mode of action

The molecluar mechanism of a pesticide; how the chemical interacts with the pathogen. Pesticides are grouped by mode of action. Some groups of pesticides are more likely to lead to the development of resistance than others.

Fumigant

A toxic gas or volitile substance that is used to disinfest soil of various pests.

Home Syllabus Lectures Labs Glossary Links

Complete GlossaryBelow is a listing of all of the glossary terms sorted by lecture. Either scroll to the lecture that you wish to see or use the links below.

Symptoms Signs Oomycetes Ascomycetes and Deuteromycetes Basidiomycetes

Other fungi and fungal-like organisms Nematodes Viruses

Bacteria Parasitic plants Epidemiology Diagnosis Pathogenesis General control terms Host resistance Chemical control

Symptoms

Symptom


Sign


Local symptom

Symptoms restricted to a particular part of the plant.

Systemic symptom

Symptoms distributed throughout the plant by internal movement.

Primary symptom

Direct changes to the tissues initially infected by the pathogen

Secondary symptom

Indirect or subsequent changes in tissues away from the site of initial infection

Abortion

The halt in development of an organ after partial differentiation.

Abscission

Premature drop of leaves, flowers or fruit resulting from the premature formation of the abscission meristem.

Anthocyanescence

A reddish or purplish coloration of leaves resulting from abnormal development of anthocyanin pigments.

Bark roughening

The formation of rough bark where smooth bark normally occurs.

Blasting

The failure to develop fruit.

Bleeding

Chronic sap flow from wounds or other lesions.

Blight

The sudden drying and browning of whole leaves, shoots or branches.

Blister

Large swollen patches on leaves, fruit, etc.

Bronzing

A coppery or bronze coloration of the leaves.

Brooming

The clustering of organs such as branches about some common point on the plant. Generally arises from development of adventitious buds.

Burl

A hard woody, often flattened, hemispherical outgrowth on a tree.

Burn

See Scorch.

Callus

Tissue overgrowth produced in response to injury or other irritation and which tends to cover a wound, canker, etc.

Canker

A sunken necrotic lesion beginning in the bark of branches, trunk, or roots and usually becoming deeper and wider by normal or accelerated secondary growth (callusing) of cambium, phellogen, and traumatic meristem. This deepening continues as the pathogen encroaches transversely into the cambium and wood as well as tangentially in the cambium region. A typically well-developed canker is a symptom complex exhibiting necrotic, atrophic and hypertrophic symptoms.

Cast

See Abscission.

Chlorosis

Yellowing of green tissue due to chlorophyll destruction or failure of chlorophyll formation.

Curl

Abnormal bending or curling of leaves or shoots due to localized overgrowth on one side or in certain tissues.

Damping-off

A symptom complex characterized by rapid dying, browning, and rotting of germinating seedlings. Shoots may be killed before before emergence, stems may be attacked in the root collar region causing shoots to fall over, roots may be destroyed, or cotyledons may be attacked.

Decay

See Rot.

Defoliation

Loss of leaves through abscission.

Dieback

The progressive drying, shrivelling, and browning of twigs or branches from the tips inward toward the trunk.

Drop

Premature abscission of fruit or twigs.

Dwarfing

Subnormal size of a plant or some of its organs.

Epinasty

A leaf curl in which the leaves turn downward, due to a more rapid growth of cells on the upper side than on the lower side of the leaf stalk.

Etiolation

A symptom complex in which the major symptoms are dwarfing of foliage and inflorescence, spindly stem growth, and chlorosis.

Exudate

See Ooze.

Fasciation

Flattening or cohering of organs such as stems, flowers, and roots. The cause is unknown, but in some cases the condition can be propagated.

Flagging

Loss of rigidity and drooping of leaves and young shoots preceding whole plant wilting.

Gall

A pronounced tumefaction, often more or less spherical and usually composed of undifferentiated cells.

Girdling

Tangential enlargement of a canker or lateral coalescence of cankers causing a branch or stem to be encircled and resulting in the complete stoppage of conduction.

Greening

See Virescence.

Gummosis

The formation of gums by diseased cells and tissues and the extrusion of gum from wounds and other lesions.

Hairy root

Abnormal number of fine fibrous roots frequently making compact clusters.

Heterotropy

The adventitious development of normal tissues or organs in unusual areas.

Hydrosis

A water soaked, translucent appearance of leaves, fruits and green stems due to the extrusion of water from the cells into the intercellular spaces.

Hyperplasia

An abnormal increase in number of cells in a particular tissue or organ.

Hypertrophy

An abnormal increase in the size of a plant or plant part generally due to an abnormal increase in the size of the cells.

Hypoplasia

An abnormally small number of cells in a particular tissue or organ.

Hypotrophy

An abnormally small plant part generally due to abnormally small cells.

Knot

A type of tumefaction.

Leaf retention

The abnormally long retention of leaves usually resulting from a failure to develop the abscission meristem.

Lesion

A localized area of diseased tissue.

Mosaic

Pale green mottling of leaves.

Mottle

An irregular pattern of indistinct light and dark areas.

Mummy

A dried shriveled fruit that is generally the result of a fungal disease.

Necrosis

The death and disintegration of cells and tissues.

Oozes


Pitting

Superficial depressions in the surface of succulent organs resulting from the death and shrinkage of subepidermal cells.

Prolepsis

Premature development of a shoot from a bud.

Proliferation

Continued or extended development of a plant part beyond the point at which growth normally ceases.

Reddening

The loss of green color from chlorophyllous tissue due to the destruction of the chlorophyll and/or the degeneration of chloroplasts which unmasks red pigments. Reddening may also result from the production of decomposition products accompanying death and deterioration.

Resinosis

The flow of resin or pitch from wounds or other lesions in conifers.

Restoration

The development of tissues or organs that normally would be only rudimentary.

Rosetting

A shortening of internodes through failure to elongate, which results in a crowding of the foliage.

Roll

See Curl.

Rot

The disintegration and decomposition of dead tissues.

Russeting

Rough or corky surfaces formed where they do not normally occur.

Scab

A limited, more or less circular, raised, and sometimes roughened lesion on fruits, tubers, leaves, and stems resulting from an overgrowth of epidermal, cortical, and peridermal tissues. This overgrowth is usually accompanied by rupturing and suberization (corking of cell walls).

Scaling

The formation of scales or corky material where scales normally do not occur.

Scorch

A sudden drying and browning of large, indefinite areas on leaves and fruits. Also damage to bark resulting in drying and death.

Shelling

Large scale loss of leaves through premature abscission.

Shot-hole

Holes in leaves caused by the falling out of killed spots of tissue.

Silvering

A silvery sheen or gray luster of leaf or primary bark surfaces due to the development of unnatural air spaces beneath the epidermis

Spike top

Death of the entire crown of a tree causing a pattern that resembles staghead.

Spot

Circular, areolate, or irregular discolored and dead areas on leaves, fruits, or green stems.

Staghead

Dieback or flagging of entire large branches in the crown, or of the entire top of a tree.

Streak

Elongated, narrow, lesions which are first water soaked then brown, in foliage or green stems. In wood there is discoloration in axial streaks within the outer, conducting layer of sapwood resulting from deterioration of the wood structure or extraneous components.

Stripe

The streak symptom in monocots.

Stunting

A type of dwarfing in which the entire plant is subnormal in size.

Suppression

The complete prevention of organ development.

Tumor

Local swelling on any part of the plant, usually woody roots, stem, or branches, usually resulting from stimulation of the plant meristem by the pathogen.

Variegation (also breaking)

Loss of color in streaks in petals of flowers.

Virescence

The process in which a normally white or colored tissue develops chlorophyll and becomes green.

Wart

A horny, hardened protuberance.

Water Soaking

See Hydrosis.

Wilting

A flaccid appearance of leaves and shoots resulting from a temporary or permanent loss of turgor due to excess transpiration by the leaves and shoots.

Witches' broom

A type of overgrowth in which there is an abnormal bushlike development of many weak shoots or roots.

Yellowing

The loss of green color from chlorophyllous tissues, due to the destruction of the chlorophyll and/or degeneration of the chloroplasts, which unmasks yellow pigments.

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Signs

Symptom


Sign


Bacterial streaming

Observation of bacteria and bacterial products streaming out of plant tissue and into water.

Ooze


Egg


Egg Mass


Cyst


Hypha


Mycelium

A mass of hyphae.

Rhizomorph

Macroscopic rope-like strand of compacted tissue formed by certain fungi.

Sclerotia


Stroma

Macroscopic mass of hyphae, usually flattened and containing fruiting structures.

Spore

Reproductive propagule of fungi and Oomycetes.

Sporocarp

Fungal fruiting body, any structure that produces spores.

Pustule

Small blister like elevation of epidermis created as spores form underneath and push outward.


Oomycetes

Hypha


Coenocytic hyphae

Hyphae without crosswalls, found in Oomycetes, some other protists and some fungi.

Oospore

Sexual spore produced by Oomycetes characterized by a thick cell wall, this is the resting or survival stage.

Oogonium

Female gamete of Oomycete that is fertilized by an antheridium to form an oospore.

Antheridium

Male gamete of Oomycete that fertilize an oogonium to form an oospore.

Sporangium

Non-motile asexual spore produced by Oomycetes, lemon or globulose in shape.

Sporangiophore

A specialized hyphae that produces sporangia.

Zoospore


Germ tube

The early growth of mycelium from a germinating spore.

Groups of Oomycetes you should know

Pythium - Important cause of damping off and root rots.

Phytophthora - Species in this genera cause late blight of potato, sudden oak death and other root rots, fruit rots, cankers and diebacks.

Aphanomyces - Important casue of damping off and root rots.

Downy mildew - A group of several genera of Oomycetes that cause foliar diseases on many different plant species, characterized by production of sporangiophores on the the lower surface of leaves.


Ascomycetes and Deuteromycetes

Septate

Having cross walls in a hypha or spore. A cross wall is called a septum.

Germ tube

The early growth of of a hypha produced by a germinating fungus spore.

Apressorium

The swollen tip of a hypha or germ tube that facilitates attachment and penetration of the host by a fungus.

Haustorium

A specialized fungal hyphae that enters and absorbs nutrients from a host cell.

Ascomycetes

Fungi in the Phylum Ascomycota that produce sexual spores in sac-like structures called asci.

Deuteromycetes

A group of fungi with no known sexual stage. Often, when a sexual stage is discovered, these fungi turn out to be Ascomycetes.

Anamorph

The imperfect or asexual stage of a fungus.

Teleomorph

The perfect or sexual stage of a fungus.

Conidia

Asexual, non-motile spores of fungi.

Conidiophore

A specialized hypha that produces conidia.

Ascocarp

Fruiting body of Ascomycetes that contain the asci and ascospores.

Asci

A sac-like structure that contains ascopores.

Ascospores

Sexual spores of Ascomycetes produced in an ascus.

Apothecia

An open cup-shaped ascocarp.

Perithecia

A flask-shaped ascocarp with an opening for releasing spores.

Cleistothecia

An ascocarp where the asci are completely enclosed.

Sporodochium

An asexual fruiting structure consisting of a cluster of conidiophores woven together on a mass of hyphae.

Pycnidium

A flask-shaped asexual fruiting body with an opening for releasing spores..

Acervulus

A subepidermal, saucer-shaped, asexual fruiting body producing conidia on short conidiophores.

Synnema

An asexual fruiting body consisting of fused conidiopores to form a stalk with conidia on the end.

Chlamydospores

A thick-walled asexual spore formed by the modification of a hyphal cell.

Sclerotia


Groups of Ascomycetes and Deuteromycetes to know

Taphrina - Species in this genus have naked asci and cause various leafg curl diseases.

Powdery Mildew - A group consisting of several genera of fungi that cause foliar diseases on many different plant species characterized by white surface mycelium, chains of condia (giving the leaf surface a powdery appearance) and production of cleistothecia.

Verticillium - Two species in this genus cause of Verticillium wilt, an important vascular wilt. The fungus has a wide host range and produces microsclerotia.

Colletotrichum - Species in this genus cause anthracnose diseases on many different plant hosts. Anthracnose diseases are characterized by blackened sunken leasions. Colletotrichum species produce acervuli.

Fusarium - Species in this genus (most commonly Fusarium oxysporum) cause Fusarium wilt of many different plant species. Fusarium oxysporum produces microconidia, macroconidia and chlamydospores.

Alternaria - Species in this genus cause lesions and blights on many different host species. Alternaria species produce dark, multicellular conidia in chains.

Septoria - Species in this genus cause lesions and blights on many different host species. Septoria species produce long, thin conidia in pycnidia.


Basidiomycetes

Basidiomycetes

Fungi in the Phylum Basidiomycota that produce sexual spores on a basidium.

Basidiocarp

Fruiting body of Basidiomycetes that contain the basidia and basidiospores.

Basidium

A club-shaped structure that prodcued basidiospores.

Basidiospores

Sexual spores of Basidiomycetes prodcued on basidia.

Dikaryotic hyphae

Hypahe with two haploid nuclei. This is the normal vegetative state for Basidiomycetes.

Clamp connections

Specialized hyphal structure that maintains the dikaryotic condition of Basidiomycete hyphae.

Telia

Rust and smut fruiting bodies that produce teliospores.

Teliospores

Overwintering spores of rusts and smuts that produce basidia and basidiospores.

Aecia

Rust fruiting bodies that produce aeciospores.

Aeciospores

Dikaryotic spore of a rust fungus produced in an aecium; in heteroecious rusts, a spore stage that infects the alternate host.

Spermatia

Male gametes of rust fungi.

Spermagonia

Rust fruiting bodies that contain receptive hyphae and produce spermatia.

Receptive hypha

The part of a rust fungus spermogonium that receives the nucleus of a spermatium.

Uredia

Rust fruiting bodies that prodcue uredospores.

Uredospores

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.

Macrocyclic

Rusts that produce all five spore types.

Microcyclic

Rusts that lack one or more of the five spore types.

Heteroecious

Rusts that require two different hosts to complete their life cycle.

Autoecious

Rusts that complete their life cycle on a single host.

Groups of Basidiomycetes to know

Rusts

Smuts

Wood rotting fungi

Rhizoctonia


Other fungi and fungal-like organisms

Myxomycetes

Slime molds - Fungal-like protists that can cause disease by growing on the surface of plants

Plasmodiophoromycetes

Fungal-like protist that cause a few important plant diseases. They produce resting spores and zoospores.

Zoospore


Resting spore

Long term survival spores produced by Plasmodiophoromycetes.

Chytridiomycota

Chytrids - True fungi that lack true mycelium. They produce resting spores and zoospores with a single flagellum.

Zygomycetes

Group of fungi with coenocytic hyphae that produce thick walled resting spores called zygospores and sporangiospores.

Zygosporangia

Thick-walled sexual spores produced by Zygomycetes.

Sporangiospores

Asexual spores produced in a sporangium by Zygomycetes.

Genera of other fungi and other fungal-like organisms to know

Physarum - Genus of slime mold causing disease on turf

Plasmodiophora - Genus of Plasmodiophoromycetes causing club root of cabbage

Spongospora -Genus of Plasmodiophoromycetes causing powdery scab of potato

Rhizopus - Genus of Zygomycetes that are oppotunistic pathogens casuing soft rots mainly on fruit


Nematodes

Nematodes

Nematoda - Phylum of worm-like animals. Soil dwelling and plant parastic nematodes are microscopic.

Stylet

A long, slender, hollow feeding strcuture used by plant parasitic nematodes.

Ectoparasite

A parasite that feeds from outside the host.

Endoparasite

A parasite that enter and feed from inside the host.

Sedentary

Describes a life style of plant parasitic nematodes that stay in one place and set up a feeding site.

Migratory

Describes a life style of plant parasitic nematodes that move through the host as they feed.

Egg


Egg Mass


Cyst


Juvenile

Immature, non-reproductive stage of nematodes.

Giant cells

Syncytial structure produced by Meloidogyne spp. as a feeding site.

Syncytia

A large, multinucleate, cell-like structure.

Groups/Genera of nematodes to know

Meloidogyne - Root knot nematodes, these sedentary endoparasites form galls on plant roots.

Heterodera and Globodera -Cyst nematodes, these sedentary endoparasites produce cysts on plant roots. Heterodera glycines - Soybean cyst nematode.

Pratylenchus - Lesion nematodes, these migratory endoparasites cause lesions on roots.


Viruses

Virus

A submicrscopic obligate parasite consisting of nucleic acid and protein.

Viroids

Small RNAs that can infect a host and cause disease

Nucleoprotein

Refering to viruses, which consist of nucleic acid and protein

Submicroscopic

Particles too small to be seen with a compound microscope

Multipartite/Multiparticulate

Refers to viruses which are packaged in multiple particles

Coat Protein

Protein, encoded by virus nucleic acid, which covers the viral nucleic acid

Inclusion body

Aggregation of virus partilces in a host cell that is visible with a compound microscope

Plasmodesmata

A connection across a plant cell wall that connects the cytoplasm of two neighboring cells

Movement Protein

Protien, encoded by virus nucleic acid, that facilitates the movement of the virus through the plant and/or by the vector

Vector transmission

Transmission of a pathogen from plant to plant by another organism

Mechanical transmission

Refers to virus transmission from plant to plant by infected plant sap

Non-persistant transmission

Refers to vector trasmission of a virus where the vector quickly picks up virus particles on its mouthparts and is infective for a short period of time (hours).

Semi-pertsistant transmission

Refers to vector trasmission of a virus where virus particles enter the vectors foregut. In this case the vector also picks up the virus quicly but is infective for somewhat longer (days) than with non-persistant transmission.

Circulative transmission

Refers to vector trasmission of a virus where virus particles must circulate through the vectors hemolymph and enter the salivary glands to be tramsitted. In this case the vector aquisition and retention time is longer than with non or semi-persistant transmission.

Propagative transmission

Refers to vector trasmission of a virus where virus particles are repliacted in the the vector. In this case the vector retention time is longer than with circulative transmission and, in some cases, the virus can be transovarially transmitted.

Transovarial transmission

Refers to viral transmission from an insect vector to its offspring, meaning offpring of an infected vector are also infective.

Aquisition period

Refers to the period of time need for a virus vector to aquire a virus while feeding on an infected plant host.

Inoculation period

Refers to the period of time need for a virus vector to transmit a virus while feeding on an uninfected plant host.

Latent period

Refers to the period of time before a vector is infective after picking up the virus from an infected host.

Hemolymph

Fluid of an insects circulatory system, "insect blood"

Viruses to know

Tobacco mosiac virus (TMV) - Highly stable, rod-shaped virus that is an important pathogen of tobacco and other solanaceous crops. It was the first virus to be discovered.

Cucumber mosiac virus (CMV) - Multipartite, isometric virus that is an important pathogen of many plants, most importantly cucumbers, melons, peppers, beans, bananas and brassicas.

Potato virus Y (PVY) - Flexuous rod-shaped virus that is an important pathogen of potato and other solanaceous crops.

Papaya ringspot virus (PRV) - Flexuous rod-shaped virus that is an important pathogen of papaya. It almost destroyed papaya production in Hawaii until a genetically engineered resistance was developed.

Tomato spotted wilt virus (TSWV) - Spherical virus with a membrane enclosing the nucleoprotien that is an important pathogen with a wide host range.


Bacteria

Bacteria

Large group of ubiquitous single celled prokaryotes.

Extracellular polysacharide

Substance produced and excreted by bacteria for protection and/or adherance. It is what gives bacterial colonies a "slimy" appearance when grown in culture.

Flagellum

A long whip-like structure used by bacteria for movement.

Pili

Hair-like appendage of found on the surface of a baterium. Used for conjugation with another bacterium.

Plasmid

Small, circullar, extrachromosomal DNA found in bacteria.

Gram positive

Refers to a group of bacteria with one membrane in association with their cell wall.

Gram negative

Refers to a group of bacteria with two membranes in association with their cell wall.

Fission

Refers to bacterial reproduction by simple cell division.

Quorum sensing

Dependence of bacterial behavior and pathogenicity on thier cells reaching a certain density by sensing the concentration of certain signal molecules.

Phage

Virus that attacks bacteria.

Transposons/Insertion elements

A segment of chromosmal DNA that can move around in the genome.

Natural transformation/competence

When a bacterial cell takes up DNA from the environment.

Ti-plasmid

Tumor inducing plasmid of Agrobacterium tumefaciens that causes gall formation and opine production by infected plants.

Opines

Nitrogen and sugar source used by Agrobacterium tumefaciens.

Type three secretion system

Protein sectretion system used by some bacteria to inject bacterial proteins into a host cell.

Stomates

Microscopic pores on plant leaves used for gas exchange.

Plant pathogenic bacterial genera and species to know

Pectobacterium and Dickeya spp. - Soft rot pathogens.

Agrobacterium tumefaciens - Causal agent of crown gall.

Pseudomonas syringae - Large group of plant pathogenic bacteria with more host specific pathovars that are important pathogens of many crops.

Ralstonia solanacearum - Causal agent of bacterial wilt.

Citrus greening disease - Important bacterial disease of citrus.

Erwinia amylovora - Causal agent of fire blight, an important disease of apple and pear.

Streptomyces spp. - Large group of common, antibiotic producing, filamentous bacteria. Streptomyces scabies causes common potato scab.


Parasitic plants

Plant parasitic plants

Vascular, flowering plants that get nutrients directly from the host plant. These plants have a close relatioship with the host plant. They have specialized structures (haustoria) to enter the host's vasuclar tissues and retrieve nutrients.

Haustoria

Specialized structure, a modified root, of a parasitic plant that enters the host host plant and obtains nutrients. (The same term is used for a specialized fungal hyphae that enters and absorbs nutrients from a host cell.)

Hemiparasites

Parasitic plants that have chlorphyl and can make some of their own sugar but still rely on thier host for water and other nutrients.

Holoparasites

Parasitic plants that do not have chlorphyl and rely on thier host for all nutrients.

Climbing vines

A group of plants that have roots and grow in the soil, but still damage other plants by growing over them and restricting photosynthesis and/or vascular systems.

Parasitic plant genera to know

Phoradendron spp. - Leafy mistletoe (genus found in the United States) is a semi-parasitic plant that parasitizes hardwoods.

Striga spp. - Witchweed is a semi-parasitic plant that parasitizes many crop species, mainly in Africa and Asia.

Cuscuta spp. - Dodder is a true parasite that parasitizes many crop species in many areas of the world.

Arceuthobium spp. - Dwarf mistletoe is a true parasite that parsitizes conifer trees.


Epidemiology

Epidemic

A disease increase in a population; usually a widespread and severe outbreak of disease.

Epidemiology

The study of factors affecting the outbreak and spread of disease.

Disease incidence

The number or poroportion of individuals that are diseased.

Disease severity

The amount or proportion of tissue that is diseased.

Disease progress curve

A graph that plots disease vs. time.

Polycyclic disease

A disease with several cycles each year (or growing season) of inoculum production and infection.

Monocycic disease

A disease where only one disease cycle is completed each year or growing season.

Primary inoculum

Inoculum that produces the first infection of plants in a year or growing season.

Secondary inoculum

Inoculum produced by previous infections that infect in the same year or growing season.

Inoculum density

The number of infective units in a given volume or area.

Disease-gradient curve

A graph that plots disease vs. distance from an inoculum source.


Diagnosis

Selective medium

Medium used to isolate a target organism, and no other organisms. These media are designed to enhance growth of the target organism while inhibiting growth of non-target organisms.

Differential medium

Medium that differentiates between the target organism and all others that may grow on that particular medium. Differentiation is often based on color.

Indicator plants

Certain plant species or cultivars that show characteristic symptoms of infection.

Differential hosts

Host range can be tested and compared to known pathogens for identification

Antibodies

A type of protien produced by vertebrate immune systems to detect harmful substances.

Antigens

Substances, ususally proteins, detected by antibodies.

ELISA

Enzyme linked immunosorbent assay - a test used to detect antigens. Antibodies can be created to detect pathogen proteins.

PCR

Polymerase chain reaction - technique to amplify sequences of DNA. Can be used to detect specific sequences of pathogen DNA.

DNA fingerprinting

Technique for pathogen identification where restirction enzymnes are used to cut genomic DNA, producing a pattern specific to a pathogen.


Pathogenesis - Terms comming soon


Plant Disease Management Strategies

Avoidance

Prevent disease by selecting a time of the year or a site where there is no inoculum or where the environment is not favorable for infection.

Exclusion

Prevent the introduction of inoculum.

Eradication

Eliminate, destroy, or inactivate the inoculum.

Protection

Prevent infection by means of a toxicant or some other barrier to infection.

Resistance

Utilize cultivars that are resistant to or tolerant of infection.

Therapy

Cure plants that are already infected.

Other terms related to disease management

Antagonism

The activity of any organims that suppresses the activity of a pest organism. An antagonist is not autmatically a biological control agent, but antagonists are used to create biological controls.

Crop rotation

Planting of different crops in the same area in sequential years (or seasons) to balance fertility and reduce the build up of crop pests.

Integrated Pest Management

The attempt to prevent pests from causing economic damage by using a variety of management methods that are cost effective and cause the least damage to the environment.


Host resistance

Interaction phenotype

The phenotypic reaction of a plant to an interaction with a potential pathogen at a given point in time and environment.

Susceptible

Phenotypic expression related to extensive symptom development and/or pathogen reproduction and accomplished by uninhibited invasion of host by pathogen.

Resistant

Phenotypic expression related to complete or partial suppression of symptom severity and/or pathogen reproduction and accomplished by arrested or slowed invasion of host by pathogen.

Partial resistance

Expression of symptoms, but less than full susceptibility or greater than complete resistance.

Non-host reaction

No interaction of pathogen and host; the pathogen is unable to infect the plant because the plant is not a host.

Hypersensitive response

Plant responds to pathogen infection by quickly killing the infected cells, blocking the advance of the pathogen.

Pathogenicity/Virulence

Refers to the ability of a microbe to cause disease (invade, infect, cause symptoms, reproduce).

Avirulence

Refers to the inability of a pathogen to cause disease.

Race

A genetically and often geographically distinct mating group within a species; also a group of pathogens that infect a given set of plant varieties.

Aggressiveness

Virulent forms of pathogen cause differing degrees of symptom severity.

Single gene resistance

Resistance attributed to the function of a single gene. Often confering complete resistance or hypersensitive response.

Polygenic resistance

Resistance attributed to the function of multiple genes. Often confering partial resistance.

Race specific resistance

Resistance that is effective against only one race of a pathogen and not other races of the same pathogen.

Rate-reducing resistance

Partial resistance where that pathogen is able to infect the plant but reproduction is reduced or eliminated thereby reducing the spread of the pathogen.

R gene

Resistance gene, a plant gene that confers resistance to a pathogen.

Avr gene

Avirulence gene, a pathogen gene whose product is recognized by a plant and leads to a resistant reaction in the plant.

Avr protein/effector

A pathogen protein that is recognized and leads to a resistant reaction in resistant plants but that is often a virulence factor in susceptible plants.

Systemic aquired resistance

Whole plant resistance response that occurs following an earlier localized exposure to a pathogen.

Transgenic plants

Plants that have been genetically manipulated to express a gene from a different species.


Chemical control

Preventative

Refers to a chemical control method aimed at preventing infection of the pathogen.

Curative

Refers to a chemical control method aimed at inhibiting the development of an established infection.

Protectant

Refers to a chemical meant to reside on the plant surface as a preventative control measure.

Systemic

Refers to a chemical meant to be taken up by and distributed throughout the plant as a preventative or curative control measure.

ED 50

Effective dose, the amount needed to have the desired effect in 50% of the population.

Active ingredient

In pesticides, the chemical responsible for the desired effect.

Mode of action

The molecluar mechanism of a pesticide; how the chemical interacts with the pathogen. Pesticides are grouped by mode of action. Some groups of pesticides are more likely to lead to the development of resistance than others.

Fumigant

A toxic gas or volitile substance that is used to disinfest soil of various pests.

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Documents

Introductory Plant Pathology