Plant Pathology


What is Plant Pathology? Plant Pathology is defined as the study of the organisms and environmental conditions that cause disease in plants, the mechanisms by which this occurs, the interactions between these causal agents and the plant (effects on plant growth, yield and quality), and the methods of managing or controlling plant disease. It also interfaces knowledge from other scientific fields such as mycology, microbiology, virology, biochemistry, bio-informatics, etc.

What is Plant Pathology? Plant Pathology is defined as the study of the organisms and environmental conditions that cause disease in plants, the mechanisms by which this occurs, the interactions between these causal agents and the plant (effects on plant growth, yield and quality), and the methods of managing or controlling plant disease. It also interfaces knowledge from other scientific fields such as mycology, microbiology, virology, biochemistry, bio-informatics, etc.

Abiogenesis: The concept of the living from non-living matter.

Abiotic: Disease not due to any microorganism but due to abiotic factors: also known as physiological or non-pathological disease.

Acervulus: A saucer shaped asexual fruiting body in Deuteromycetes producing conidia on conidiophores.

Acropetal Arrangement :Development of spores from the base to upward , with the youngest at the apex.

Acquired Resistance :Non-inherited or adapted resistance.

Acquistion Feeding :The period for which a vector after feeding on a virus affected plant becomes viruliferous or infective.

Actinomycetes :A group of bacteria, forming branching filaments, mostly Gram + ve and anaerobic.

Adsorption :Process by which the liquid is imbibed to and held on the surface.

Adult Plant Resistance: Resistance expressed at the adult plant stage and not expressed by seedlings.

Agro – Ecosystem: An agricultural area sufficiently large to permit long term interactions between all living organisms and their non-living environment.

Air – Borne :Organisms transported from place to place through air.

Alleloparasitism :When partners change their role while living together.

Alternate Host :Host other than parent host to complete life cycle of the parasite.

Alternation of Generation :The occurrence of two or more distinct forms or generations in the life cycle of an organism.

Anaerobic Respiration :Respiration in the absence of oxygen.

Anaerobic Fermentation: Fermentation in the absence of oxygen strictly by anaerobic bacteria or yeasts.

Anamorph :Asexual or imperfect or conidial state or stage of a fungus.

Anisogametes :Motile gametes similar in structure or morphology but differing in size.

Anisogamy :Union of two morphologically similar planogametes but differing in size.

Antheridium :The male sexual organ or male gametangium present in some fungi.

Anthracnose :A disease characterized by black, sunken lesions on stems, twigs, leaves or fruits.

Antibody :A protein produced by certain white blood cells in response to a foreign body.

Antibiosis :The inhibiting effect of a volatile or non-volatile toxic compound and active against competing fungi.

Antibiotic :A substance produced by one microorganism and inhibiting or killing the other microorganism.

Antidote :A substance used to counteract the effects of a poison.

Apoplastic movement :Movement in the direction of the transpiration stream, also called as acropetal or upward movement.

Apothecium :An open saucer shaped ascocarp in Discomycetes , bearing asci and ascospores.

Appresorium :The swollen flattened tip of hypha that helps in the attachment to host surface and later penetration by the fungus.

Arthrospore :A spore resulting from the fragmentation of a hypha at the septum.

Ascocarp :Fruiting body in Ascomycetes containing or bearing asci.

Ascogonium :The female gametangium or sexual organ in Ascomycetes.

Ascogenous hypha :A specialized hypha which gives rise to asci.

Ascus :An elongated sac like structure usually containing eight ascospores produced by free cell formation.

Assimilation :Utilization by a living organism of absorbed food material for different processes such as growth , reproduction and repair.

Atrophy :Degeneration or under development of a plant part or an organ.

Atropine :An antidote used for the treatment of organophosphate and carbamate poisoning.

Autoecious Fungus :Fungus completing its entire cycle on the same host.

Axenic culture :Micro-organisms growing in the absence of the host.

Auxin :Hormonal substances responsible for growth promotion, by cell enlargement.

Azotobactor :Free living aerobic nitrogen fixing bacteria.

Bacteria :Unicellular prokaryotic organisms usually lack chlorophyll and multiply by fission.

Bacteriophage :A virus that is parasitic within bacterium.
Bacteriocin :Substance produced by certain bacteria and active against one or more strains of the same or closely related species.
Bacteriostatic :An agent that prevents multiplication of bacteria without killing them.
Basipetal :Development of spores with the oldest at the apex.
Basidiocarp :The entire fructification of Basidiomycetes bearing basidia.
Basidium :A structure bearing on its surface a definite number of basidiospores , those are usually formed following karyogamy and meiosis.
Binomial nomenclature :A system of classification introduced by Linnaeous, composing of two names, the first as genus and second the species.
Binal viruses :Viruses having polyhedral head with helical tail.
Biocide :A chemical toxic to a living organism.
Biotroph :An organism that can live and multiply only on another living organism.
Black heart :A storage disease due to the lack of oxygen in poor ventilation conditions.
Blight :General and rapid killing of leaves , flowers or stems.
Blister :A raised lesion on the leaf surface , which opens to expose spores.
Blotch :A disease characterized by large irregular spots or blots on leaves , shoots or stems.
Botanical pesticide :A pesticide obtained from plants.
Bromoviruses :Viruses having rounded particles.
Brown rot :When hemicellulose and celluloses in the wood are decomposed except lignin, giving brown colour.
Budding :A bubble like structure protruding from the hypha and separated by constriction of wall from the parent hypha.
Canker :A necrotic often sunken lesion on a stem , branch , twig or fruit , arising from destruction of epidermal or cortical tissues.
Capsid :The protein coat covering nucleic acid in case of viruses.
Capsule :A layer of polysaccharides around bacterial cell for protection from adverse environment.
Carcinogen :A substance capable of producing cancer.
Carrier :A liquid or solid material added to a chemical compound to prepare a proper formulation. A source of infection for other plants.
Caulimovirus :Virus containing circular double stranded DNA.
Cell :Mass of protoplasm bounded by a wall or membrane. It is the basic unit of structure of all living organisms except viruses.
Cellulose :The main constituent of cell wall. A polysaccharide composed of glucose units linked by glycosidic bonds.
Chemotherapeutant :Fungicides those act on the pathogen by entering into plant system.
Chitin :Nitrogen containing compound found in cell walls of fungi.
Chlorosis :Yellowing of normally green tissues due to destruction of chlorophyll or failure of chlorophyll formation.
Chromosome map :Map showing relative position of genes.
Clamp connection :Outgrowth of hyphae those form bridges around septa , thus connecting two cells.
Coenocytic :Not septate ; refering to the fact that the nuclei are embeded in the cytoplasm without being separated by cross walls.
Collar rot :Rotting of stem or main axis at or about the level of soil.
Commensalism :A type of symbiosis in which two species live in close association when one member benefits but with no harm to the partner.
Compound interest disease :when there are many generations of the pathogen in the life of the crop and disease is generally widespread.
Constitutional dormancy :A condition where in the development is delayed due to an innate property of dormant stage.
Cultural control :Method of pest control by means of skillful combination of agronomic practices.
Cyst nematode :A carcass of dead females containing viable eggs in genus like Heterodera.

Damping off :Sudden collapse , death and rotting of seedlings at soil level resulting from the attack of Pythium spp.
Deficiency disease :A disease caused by inadequate intake of any essential macro or micronutrient.
Dermatomycosis :A fungus infection of animal or human skin.

Die back :Progressive death of shoots from tip and progressing backward towards the main stem.

ELIZA : It is the abbreviation of Enzyme Linked Immunosorbent Assay; an important biological test for the valid identification of plant viruses and bacteria.

Gene cloning : Isolation and multiplication of an individual gene or gene sequence by inserting into a bacterium or yeast cell for replication.

Gene :Unit of hereditary present on a chromosome in a bead like structure.

Genetic engineering : Transfer of a specific gene between organisms.

Genetic recombination :Variation in genetic make up of an offspring.

Genome : The entire genetic information of an organism.

Genotype : The genetic constitution of an organism.

Genus : A taxonomic category including a number of species.

Germination : Ability of seed to develop into a normal plant under favourable conditions.

Germ tube : A thread like structure coming out of the germinating spore.

Gibberellins : A group of plant growth regulating substances with a variety of functions.

Girdling : Surrounding stem and completely cutting off water supply and causing death.

Growth regulator : A natural substance that regulates the enlargement , division or activation of plant cells.

Gamete : A male or female reproductive cell.

Gummosis : Production of gum by or in a plant tissue.

Guttation : Exudation of water partially along leaf margins.

Halophytes : Plants able to tolerate high salinity.

Hectare :An area of land equal to 2.47 acres.

Hemibiotrophs : Organisms those attack living tissues but may continue to sporulate after the tissue is dead.

Heterotrophic : Requiring an organic source of energy , not producing their food  of their own but depend on other host for getting nutrition.

Histology : Science dealing with tissues and their organization.

Homothallic : A fungus producing male and female gametes on the same mycelium.

Host range : The number of hosts attacked by a pathogen.

Pandemic : A wide spread and destructive outbreak of disease simultaneously in several countries.

Parasitism : A type of symbiosis , in which a parasite depend on the host for essential food.

Pathogen : Any organism capable of causing a disease.

Pathogenesis : The sequence of events with the start of infection till the completion of disease.

Pathogenicity : Ability of the pathogen to cause a disease and the degree of pahtogenicity is termed as virulence.

Perthotrophs : Organism which kills the host in advance of penetration.

Physiologic race : A group of micro-organism similar in morphology but differ genetically.

Physiologic specialization : Existence of number of races or forms of one species of a pathogen.

Phytoalexin : A substance produced in plants as a result of chemical, biological or physical stimuli , inhibiting growth of certain micro-organisms.

Plasmogamy : Fusion of protoplasm of two haploid cells without fusion of nuclei.

Polycyclic : Response of a plant to repeated cycles of infection under field conditions.

Polymorphic : Occurrence of more than one spore forms in the life cycle of a micro- organism.

Primary host : The host upon which the telial stage of a rust fungus is produced.

Primary inoculum : The inoculum produced as a result primary infection , that later becomes a source of secondary infection to other plants.

Prokaryote : Organisms lacking true nucleus (Bacteria and MLO).

Propagative virus : A virus that multiplies in its insect vector.

Protectant: A substance that protects an organism against infection by a pathogen.

Pustule: A small blister like elevation of epidermis.

Race: A group of biotypes with similar virulence on a particular host.

Receptive hypha: Hypha in a pycnium of a rust fungus with a female sexual function ,fertilized by a male pycniospore.

Respiration: A biochemical phenomenon where there is breakdown of carbohydrates into carbondioxide and water.

Retrovirus: An RNA virus that uses reverse transcriptase to synthesize DNA and RNA.

Rhizoids: A root like structure of thin hypha growing toward substrate.

Rickettsia: Organisms intermediate between bacteria and viruses with ability to multiply only in living plant cells.

Ring spot: A circular area of chlorosis with a green center.

Roguing: Removal of undesirable plants from the growing crop.

Rot: Softening , discoloration and often disintegration of a succulent plant tissue as a result of fungal or bacterial infection.

Scorch: Burning of leaf margins as a result of infection or unfavourable environments.

Seed pathology: Science dealing with seed-borne diseases and their management.

Seed: A mature ovule with a miniature or rudimentary plant.

Selective medium: A culture medium suitable for culturing a specific pathogen.

Shot hole: A symptom in which small diseased fragments of leaf fall off leaving small holes in the lamina or leaf.

Soft rot: Softening and disintegration of plant tissues by enzymes , produced in case of fungal or bacterial infection.

Soil amendments: Any substance added into soil for improving its physical or chemical properties.

Soil drenching: A pesticide used for application to the soil surface before or after plant emergence.

Soil-borne:Micro-organisms living and surviving in soil.

Spawn: The secondary mycelium used  in the commercial production of mushrooms.

Spawning: Placement of spawn into the substrate upon which mushrooms grow.

Species: A group of closely related individuals resembling each other in inherited characteristics.

Spiroplasma: A prokaryote with helical shape and lacking cell wall.

Sporadic disease: Diseases those occur at very irregular intervals and locations and in relatively a few instances.

Spore: A single to many celled small reproductive unit in fungi with no preformed embryo.

Sporodochium: A compact cushion like fruiting structure with short condiophores in cluster.

Sterilization: Elimination of pathogen from the surface with chemical or heat.

Stipe: The stalk of a stipitate basidiocarp or ascocarp.

Substratum: The substance on which the fungus grows.

Sun scald: Burning effect due to high sun heat.

Suppressive soil: Soils in which certain diseases are suppressed because of the presence of antagonists.

Susceptibility: Inability of the plant to resist the effect of a pahtogen.

Symptom: Visible reaction or expression on a  plant due to abiotic or biotic factors.

Syndrome: Disease picture , a group of signs and symptoms those occur together.

Synergism: Healthy association of two organism not damaging each other.

Systemic: Spreading internally throughout the plant parts.

Systemic fungicide: A fungicide translocated within the plant away from the site of application.

Thermal death point: Temperature at which all the bacterial cells in a suspension are killed after exposure for 10 minutes.

Thermophilic: Organisms those tolerate high temperature (45-65 oC).

Tinsel flagellum: A flagellum that bears hairs at the flagellar membrane.

Toxin: A compound produced by a microorganism and being toxic to a plant or animal.

Transformation: It is the transfer of genetic material.

Tumor: An uncontrolled overgrowth of tissues.

Unilateral: Hymenium found on only one side of the basidiocarp.

Variegation: Regular colour changes particularly in flower petals and leaves.

Vascular bundle: Conducting tissues consisting of primary xylem.

Vector: Insect able to transmit a virus.

Vein clearing: Destruction of chlorophyll adjacent or in the vein tissues mostly as a result of virus infection or an increased translucency or whitening of veinal system in a leaf.

Viricide: A substance capable of inactivating or suppressing the multiplication of a virus.

Viroid: Single stranded small circular naked RNA (virus particles without protein coat) replicating in host nucleus.

Virulence: Organism having a high capacity to produce disease.

Viruliferous: Insect vector with virus in its body and being capable of introducing it into a susceptible host.

Virus: Submicroscopic strictly obligate parasite filterable infective entities nucleo-protein in nature.

Vivotoxin: The toxin that can produce disease symptoms in the host plant , usually host non-specific.

Wart: Abnormal growth on the epidermis or any surface.

Wet rot: Rapid and complete disintegration of the tissues with the release of water from dead cells.

Xylem: Plant tissues in the root for upward conduction of water and minerals.

Zoosporangium: A sporangium containing zoospore.

Zoospore or swarm spores: A spore capable of moving by cilia or flagella.

Muhammad Ramzan Rafique
Muhammad Ramzan Rafique

I am from a small town Chichawatni, Sahiwal, Punjab , Pakistan, studied from University of Agriculture Faisalabad, on my mission to explore world I am in Denmark these days..

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