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Abaxial. Facing away from the axis, lower, undersurface or “back” of the leaf.

Abiotic stress. Nonliving environmental factors such as nutrient deficiency, drought, excessive heat, high winds, etc., that can have harmful effects on plants.

Abscission (adj. abscissile). The separation of leaves from a plant. This process is controlled primarily by 3 compounds, namely auxin, ethylene and abscisic acid.

Acarine. Refers or describes  the members of the Acari, an order in the class Arachnida, which includes the mites and ticks. They are characterized by an oval, one-part body and a minute to small body size.

Acervulus (pl. acervuli). The erumpent, cushion-like fruiting body bearing conidiophores, conidia, and sometimes setae.

Acid soil. Soil containing more hydrogen cations (H+) than hydroxyl anions (OH-) with the concentration of the H+ determining the acidity; soil with pH level lower than 6.0.  Generally, soil acidity is not a problem for sweetpotato at  pH 5.0 or higher.  If pH is less than 5.0, concentrations of Aluminium or Manganese may increase to toxic levels, and several nutrients become increasingly insoluble and more likely to be deficient.

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Facing toward the axis, for example the upper surface of a leaf

AdsorptionThe accumulation of gases, liquids, or solutes on the surface of a solid or liquid.

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A fully developed animal or insect, capable of reproduction.

Alkaline soil. Soil containing more hydroxyl anions (OH-) than hydrogen cations (H+)  (basic); soil with pH value greater than 7.0.  High pH makes several plant nutrients less soluble, so that deficiency is likely.  Calcium carbonate (lime or coral) is the most common cause of soil alkalinity.  Sodic soils (very high in sodium) may also be alkaline.

Alkaloid. Often toxic, bitter tasting, nitrogen-containing organic compounds released by plants.

Allelopathy (adj. allelopathic). The inhibition of growth of one plant species by another due to its release of toxic chemical substances.  Yield reduction in some intercrop combinations are suggested to be due to allelopathy.

Amphimictic. Pertains to organisms that are developed through the fusion or mixing of the egg and the sperm pronuclei.

Anaerobic. Absence of oxygen.  As most life forms rely on oxygen to mobilize energy, only specialist organisms or chemical pathways within organisms, can function in anaerobic conditions.

Anaerobic respiration. Gaseous exchange in which the hydrogen removed from the glucose during glycolysis is combined with an organic ion instead of oxygen.

Anamorph (adj. anamorphic; syn. imperfect state). the asexual form in the life cycle of a fungus, when asexual spores (such as conidia) or no spores are produced.

Androecium. Refers collectively to the stamens of one particular flower.

Anthocyanin. The scarlet, pink, purple and blue pigments that give the flowers,  leaves and storage roots their characteristic colours.

Aphids. Small, often wingless sucking insects, sometimes referred to as 'plant lice', that live on plant sap and exude sticky or waxy secretion from the abdomen. A number of aphid species can transmit viruses.  They belong to the order Homoptera.

Apical. At or pertaining to the tip (apex).

Apical dominance. Inhibition of axillary growth (branching) due to apical growth.

Appendage. Any limb or other organ, such as an antenna or leg, which is attached to the body by a joint.

Appendix. In insects, a short vein on the wing, especially a short continuation after the main vein has changed direction.

Ascoma  (pl. ascomata; syn. ascocarp). Sexual fruiting body of an ascomycetous fungus that produces asci and ascospores.

Ascomycete. A type of fungus that produces asci.

Ascospore. A sexual spore borne in an ascus (see definition below)..

Ascus (pl. asci). A saclike structure containing ascospores (typically eight) and usually borne in a fungal fruiting body (ascoma).

Asexual.  Not involving the combining of genetic information from two different individuals.  Asexual reproduction results in many individuals who are genetically identical to the parent.  In plants this may be referred to as vegetative propagation (i.e. by cuttings or sprouts)

Attractants. Substances which elicit a positive directional response; chemicals having positive attraction for animals such as insects, usually in low concentration and at considerable distances e.g. sex pheromones.

Axillary. Pertains to an axil, which is the acute angle formed by the junction of a leaf petiole and a stem. The axil contains meristematic tissue from which branches may grow.


Bacillus thuringiensis. Commonly known as B.t., is a bacterium from which a toxin is manufactured that has insecticidal properties against various insects. Compounds sold as B.t. generally contain the manufactured toxin and not the bacteria.

Basal (alt. basilar).  Refers to the base of a structure;  part closer to the stem in reference to leaves or nearer the soil line in reference to stem.

Basidiospore. Haploid (1N) sexual spore produced on a basidium.

Basidium (pl. basidia; adj. basidial). A fungal fruiting structure on which haploid basidiospores are produced externally.

Beetles. Insects belonging to the order Coleoptera, characterised by biting mouth parts and thickened forewings forming elytra or covers that protect the hindwings.

Bioassay. The use of a living material or organism to determine the biological activity and relative strength of a substance.

Biological control. The use of living things to control pests and diseases such as employing predators, parasites, or pathogens.

Biotic. Refers to any form of life.

Blade.  The expanded portion or flat surface of a leaf, frond, etc.

Blight. Refers to a disease of plants that results to sudden withering, cessation of growth, and death of parts, especially young and growing tissues.

Blister. Refers to raised dark spots which develop on the skin of storage roots, and may be sparsely scattered or numerous, covering a large proportion of the root surface.

Blotching.  An irregular patch of colour or discolouration with poorly defined edges.

Bract. A small leaf without a stem (petiole) at the base of a flower or other plant part.

Broom-like. Having many short parallel branches as in witches' broom.

Bug. Insects of the suborder Heteroptera (order Hemiptera). They are wingless or four-winged, with mouthparts adapted for piercing and sucking.

Butterfly. Any of various insects of the order Lepidoptera, characteristically having slender bodies, knobbed antennae, and four broad, usually colourful wings.


Calcareous. Refers to soils or rocks, containing abundant calcium carbonate, which results in alkaline or basic reactions (high pH) and consequently low availability of several essential plant nutrients, making them problematic for crop production.

Callus. A mass of undifferentiated swollen cells, such as may be formed on and around a wound.

Canker. A patch of dead cells or necrotic, localized, dry diseased area; may also be used to refer to the lesion itself.

Carotenoids.  Include  carotene (orange or red-orange) and xanthophyll (yellow) pigments present in most photosynthetic organisms, and functioning together with chlorophyll to capture light energy.  During autumn the chlorophyll is degraded allowing the more stable carotenoids to surface and produce the orange and yellow autumnal foliage colours.  These pigments are also give the yellow and orange colour to plant products such as carrots, tomatoes and orange-fleshed sweetpotatoes.

Caterpillar. The larva of a moth or butterfly such as the leaffolders, army worm, cut worm and horrnworm, which feed on leaves.

Cation. An ion having a positive electrical charge.

Cation Exchange Capacity (CEC): The total potential of soils for adsorbing cations, expressed in milligram equivalents per kg of soil.

Cerci. (singular: cercus) The feeler-like paired long appendages originating from the tip of the abdomen in many insects.

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A furrow or a groove on plant parts, eg. storage roots which may be caused by feeding of insects such as rough sweetpotato weevil or white grub.

Chelicera. (pl. chelicerae). The frontal pair of appendages in insects like the spiders and mites.

Chlamydospore. Thick-walled or double-walled asexual resting spore formed from hyphal cells (terminal or intercalary) or by transformation of conidial cells that can function as an overwintering stage.

Chlorophyll. The green pigment in leaves that is primarily responsible in harvesting light energy for photosynthesis. It is produced in the chloroplasts of leaf, stem and flower cells.

Chlorosis (adj. chlorotic). 
Examples of Chlorosis:
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An abnormal plant condition where there is reduction, poor development or loss of the green pigment (chlorophyll) due to any disease, disorder or physiological stress, resulting in light green, yellow or whitish colour. 

Class. A division of the animal or plant kingdom lower than a phylum and higher than an order, for example the class Insecta.

Closterovirus (from Greek kloster, "thread"). Member of a group of plant viruses with very long, flexuous, rod-shaped particles containing a single molecule of linear RNA.  Some closteroviruses are transmitted by whiteflies.

Club. The thickened tip (farthest from the head) of the antennae.

Coalesce. To fuse or merge together.

Columella. The  central sterile part of sporangium in some fungi.

Concentration. The amount of one substance contained within a unit measure of a mixture (for example, a solution or a plant tissue).

Conidiophore. Simple or branched, fertile hypha on which conidia are produced.

Conidium (pl. conidia). Asexual spore borne at the tip or side of a specialised hypha (conidiophore). There are two types of conidia, the larger one is called macroconidium (pl. macronidia) and the smaller, microconidium (pl. microconidia).

Cornicle.  Paired secretory structures on the abdomen of aphids.

Cortex. The region of tissue in a root or stem lying between the epidermis and the vascular tissue. It may function in photosynthesis, food storage, support, and growth of the plant.

Crinivirus. The genus in the family Closteroviridae such as the sweetpotato chlorotic stunt virus.

Crop damage. The adverse effect on crops due to biotic or abiotic agents, resulting in economic loss (reduction of yield and/or quality).

Crop rotation. The successive planting of different crop species; often used to improve soil fertility or to reduce disease and pest problems. 

Curling. A symptom of insect, diseases or nutritional disorder that causes leaves to roll up or down.

Cutting. A part of the vine or stem used as propagation or planting material.


Damping off (alt. dampen off).  Rapid decline of germinating seed or seedling  before or after emergence leading to death due to decomposition of the root and/or lower stem.

Decay. The gradual decomposition of plant part.

Deficiency (nutrient). Nutrient status when the concentration is below the critical level thus limiting plant growth and development.

Defoliate (n. defoliation).  To cause the leaves of a plant to fall off due to causes other than ageing or senescence; may be brought about by large number of insects feeding on the leaves. 

Depressed. Somewhat sunken.

Deutonymph. A third instar of a mite.

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

Disease. An abnormal condition or functioning of a part, organ, or system of a plant or organism resulting from various causes, such as infection, genetic defect, or environmental stress, and characterised by an identifiable group of signs or symptoms.

Disease cycle. Succession of all of events and interactions among the host, parasite and environment that occur in a disease, from initial infection of the plant or organism by a causal agent, through pathogenesis, to over-seasoning, until another infection occurs.

Disease incidence. Number of plants or organisms affected by a disease within a population.

Distal. Towards the apex or away from the point of origin.

Dorsal. On or concerning the back or top of an insect or animal.

Dwarfing. General reduction in length or height of plant due to underdevelopment of organs caused by nutritional or physiological disorder, disease, or any environmental stress.


Ectohormone. A substance secreted by an insect or animal to the outside of its body causing a specific reaction, such as determination of physiological development, in a receiving individual of the same species.

Ectoparasite. A parasite that lives on the outside of its host.

Enzyme-linked immunosorbent assay (acronym ELISA).  A serological test in which the sensitivity of the reaction is increased by attaching an enzyme that produces a coloured product to one of the reactants

Elytron (plural elytra). The thickened, leathery or horny forewing of a beetle or an earwig that protects the membranous hindwings.

Endemic. Restricted to a well defined geographical region.

Endoparasite. A parasite living inside its host.

Entomogenous. Pertaining to organisms growing in or on an insect, such as some wasps and  fungi.

Enzyme. A biological catalyst, normally a protein formed and secreted by a living cell that facilitate the conversion of a substrate molecules to a product.

Eradication. Control of plant disease by eliminating the pathogen after it is established or by eliminating the plants that carry the pathogen.

Escape. Failure of inherently susceptible plants to become diseased, even though disease is prevalent.

Excreta. The waste products of metabolism.

Exudations. Secretions or modified excretory products from epidermal glands such as wax (from bees), silk (from caterpillars), nutrient or sugary excretions (from  aphids), scents to attract other insects or the opposite sex (e.g. sweetpotato weevil).


Family. A taxonomic subdivision of an order, suborder, or superfamily that contains a group of related subfamilies, tribes and genera. Family names always end in -idae.

Filiform. Threadlike.

Flaccid. Wilted, lacking turgor or rigidity.

Flagellum (pl. flagella). Hairlike, whip-like, or tinsel-like appendage of a motile cell, bacterium or zoospore that provides locomotion.

Fleck. Minute, discoloured spot in green tissue; different from lesion.

Foliar diagnosis. Evaluation of the nutrients in a plant, or the plant nutrient requirements of a soil, by analysing the leaves.

Frass. Excreta of insects such as leaffolders, sweetpotato stem borer and sweetpotato weevils.  It is brown or blackish, and may be dry and friable or moist. It is one of the best indicators of borer presence in a vine.

Fruiting body. In fungi, any of various complex, spore-bearing reproductive structures.

Fumigant. (v. fumigate). A gas or volatile substance used to kill or inhibit the growth of microorganisms or other pests.

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


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An abnormal growth or corky localised swelling of a plant part (leaves, shoots or roots) caused by a fungus, bacterium, nematode, insect or some other organisms. Insects like gall mites, aphids, gall wasps, and gall midges and the root knot nematode produce galls on plant parts.

Gynoecium. The pistil or pistils considered as a group.

Genus. A group of closely related species (plural: genera). The name of the genus is incorporated into the scientific names of all the member species: Cylas formicarius  and Cylas brunneius, for example, both belong to the genus Cylas.

Girdle. To circle and cut through a stem disrupting the phloem and xylem.

Glabrous. Absence of hairs.

Globose. Having a spherical or globular shape.

Gram-negative.  Relates to a type of bacteria that possesses cell walls consisting  of an outer membrane and a cytoplasmic membrane. Of, relating to, or being a bacterium that does not retain the violet stain used in Gram's method.

Gram-positive bacteria. Of, relating to, or being a bacterium that retains the violet stain used in Gram's method.

Grasshopper. Any of numerous insects of the families Acrididae and Tettigoniidae (order Orthoptera). Grasshoppers usually have long, powerful hind legs adapted for jumping.

Green manure. Crop or plants grown and ploughed under to increase soil organic matter like Crotolaria juncea.

Grub. An elongate insect larva, specifically applied to Coleoptera (Scarabaeiform) and  some Hymenoptera.  Usually with C-shaped and thick body.


Hemiptera.  A large order of insects including aphids and many kinds of plant bugs characterised by piercing and sucking mouthparts.

Herbicide. A substance that kills herbaceous plants.

Homoptera. Order of insects containing cicadas, hoppers, psyllids, whiteflies, aphids and scale insects. They are characterized by uniformly leathery or uniformly membranous forewings, sucking mouthparts, and an incomplete metamorphosis.

Hormone. A chemical substance that elicit specific effects on the growth and physiology of organisms.

Honey dew. The sweet liquid emitted from the anus of aphids and some other sap sucking bugs.  Other insects feed on it as source of energy. When left on leaf surfaces, it  promotes growth of sooty mould.

Host. The organism in or on which a parasite lives; the plant on which an insect or other arthropod feeds.

Host plant. Living plant attacked by or harbouring a parasite or pathogen and from which the invader obtains part or all of its nourishment

Host range. The range of plants on which an organism, particularly a parasite, feeds.

Humidity (adj. humid).  The water content of air.

Hypha (pl. hyphae). The microscopic, multicellular, nonphotosynthetic filaments of fungi and seaweeds.

HyalineTransparent or nearly so; translucent; often used to mean colourless.


Indigenous. Native to a place.

Infection. Presence of pathogen inside a host that may subsequently lead to a disease.

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

Indicator plant.  Plant that reacts to a pathogen or an environmental factor with specific symptoms, used to detect or identify the pathogen or determine the effects of the environmental factor.

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

Infection court. Site in or on a host plant where infection can occur.

Infestation. Presence of an aggregate of insects or nematode on plant surface.

Injury. Damage from insect feeding, chemical action or any abiotic stress on plant or plant part.

Inoculum (pl. inocula). Pathogen or its parts, capable of causing infection when transferred to a favourable location.

Internal brown spot.  It is characterised by the occurrence of brown necrotic areas in the flesh, irregularly distributed but more prevalent in the cambial zone, close to the surface of the root.

Insecta. A 'class' of the 'phylum' Arthropoda, distinguished by adults having three body regions: head, thorax, and abdomen; and by having the thorax three-segmented with each segment bearing a pair of legs.

Insect vectors. Insects that carry and distribute disease-causing microorganisms.

Instar. The stage in an insect's life history between any two moults. A newly-hatched insect which has not yet moulted is said to be a first-instar nymph or larva. The adult (imago) is the final instar.

Integrated pest management (abr. IPM).  A philosophy of pest management that put together different management control measures with emphasis on environment and users' safety such as the use of biological control agents e.g. insect predators, over the use of chemicals.

Intercropping.  System of simultaneously growing two or more crops on the same piece of land.

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Part of the stem between two nodes.

Interveinal.  Refers to the surface of the leaf blade in between veins.


Juvenile. An immature form that appears similar to but usually smaller than the adult and is not sexually mature (e.g. insects with gradual metamorphosis, nematodes).


Lamella. (pl. lamellae).  A thin flat plate or laterally flattened structure.

Lamina. A blade or flat portion of the leaf; the leafy portion of a frond.

Larva. The juvenile worm-like stage of insects before reaching the adult stage such as grubs and caterpillars.

Latent. Present but not manifested or visible, as a symptomless infection by a pathogen.

Latent infection.  Infection unaccompanied by visible symptoms.

Latex. The milky sap that exudes from cut surfaces of some pant species including sweetpotato.

Leaffolder.  Insect that folds over the leaf edges, fasten them together with silk and make a nest inside; also referred to as leaf sewers.

Lenticel. A corky spot on the surfaces of stems or storage roots through which gases are exchanged between the atmosphere and the underlying tissues. 

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Well-marked, dead (brown or black), localised area caused by diseases, pests, disorders or stresses; can be interchangeably used with spot when referring to dead, brown or black distinct colour or mark on a surface.

Lignin. A complex polymer, the chief noncarbohydrate constituent of wood, that binds to cellulose fibers and hardens and strengthens the cell walls of plants. Lignify. To become woody.

Lime. Compounds of calcium (ground limestone-calcium carbonate, hydrate limestone -calcium hydroxide, or burnt lime-calcium oxide/CaO). The amount of lime in the soil determines whether it is acid, neutral or alkaline. Limestone that is worked into the soil raises the pH from an acid pH to one that is alkaline. 

Limestone. A sedimentary form of calcium carbonate and is used to alter or increase the soil's pH.

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A division of a leaf or plant part that is deeply indented.


Macronutrient. Essential element required in relatively large quantities for plant growth and development.

Major veins. Thick veins on the leaf blade directly branching from the midvein or midrib and radiating outward to the marginal veins.

Marginal. Refers to the  edges or borders of a leaf, e.g. leaf marginal chlorosis means reduction or loss of chlorophyll on the borders of the leaf.

Marginal vein. The vein that runs just inside the margin of the blade and parallel to it.

Medulla. The inner portion of a structure.

Mesothorax. The middle or second segment of the insect's body.

Micronutrient. Essential element required in relatively small quantities for plant growth and development.

Midrib. The central or main vein of a leaf that bisects the blade from the petiole to the tip.

Mildew. A fungus that leaves a thin white coating on the surface where it grows. thin coating of mycelial growth and spores on the surfaces of infected plant parts.

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Tunnel in leaves appearing like whitish blotches or trails.

Minor veins. Secondary and tertiary branches of the major veins.

Mite. Any of various small or minute arachnids of the order Acarina that are often parasitic on animals and plants, infest stored food products, and in some species transmit disease.

MLO (syn. mycoplasma like organism). Archaic term for phytoplasma; plant-parasitic pleomorphic mollicute (prokaryote with no cell wall) found in phloem tissue; cannot yet be grown on artificial nutrient media.

Morphology. The science of the form and structure of animals and plants and of their organs.

Moth. Any of numerous insects of the order Lepidoptera, generally distinguished from butterflies by their nocturnal activity, hairlike or feathery antennae, stout bodies, and the frenulum that holds the front and back wings together.

Motile.  Capable of self-propulsion by means of flagella, cilia, or amoeboid movement.

Mottled. Appearance of uneven colour due to less distinct but regularly distributed pale or purple areas contrasting with the normal colour.

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

Moult. To moult is to shed the outer covering of the body - the exoskeleton.

Mu. (µ) Greek letter used  to symbolise micro or a millionth (0.000 001 or 1 x 106).

Mummy.  A dried shrivelled plant part or organ partially or completely replaced with fungal structures.

Mycelium (pl. mycelia). The mass of interwoven filamentous hyphae that forms especially the vegetative portion of the thallus of a fungus.

Mycorrhiza (alt. mycorhiza). The symbiotic association of fungus hyphae with plant roots.


Nanometer (nm). A billionth of a meter (10-9 meters). A nanometer is the unit of measure used to measure the wavelength of visible light. For example, the thickness of a human hair is approximately 76,200 nanometers or 3 thousandths of an inch. Particles sizes in silver colloids are expressed in nanometers.

Necrosis (adj. necrotic).
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The localised death of tissue due to diseases or disorders usually accompanied by browning or blackening.

Nectary. Any place or organ where nectar is secreted.

Nematode. Small, slender, microscopic round worms which live in the soil. They may be parasitic in animals or plants, or free-living in soil or water. As parasites, they can cause damage to and even kill plants. Others can be beneficial.

Nepovirus. A multicomponent plant virus with two isometric particles containing two species of linear RNA, transmitted mechanically and by soil-inhabiting nematodes.

Nocturnal. Active at night.

Node. The place on a stem where leaf petioles are attached.

Nymph. Name given to the young stages of those insects which undergo a partial metamorphosis. The nymph is usually quite similar to the adult except that its wings are not fully developed. It normally feeds on the same kind of food as the adult.


Obtect pupa.

A pupa with appendages 'glued'  to the body by hardening of the outer cover (exoskeleton).

Occlusion. Refers to an obstruction or a closure.

Olivaceous. Olive green in colour.

Omnivorous. Refers to organisms that eat both animal and vegetable food.

Ootheca (pl. oothecae). The covering or case of an egg mass of certain insects such as grasshoppers and beetles.

Order. A subdivision of a class or subclass containing a group of related families.

Organophosphates. Organic compounds containing phosphorous; an important group of synthetic insecticides belong to this class of chemicals.

Organic.  Compounds containing carbon derived from decomposed animal or plant organisms. 

Ovipositor. Egg-laying structure at the hind end of the abdomen of  female grasshoppers.

Oxidation. The loss of electrons from an atom, compound or molecule. It is generally applied to a chemical reaction of a substance with oxygen (O2) or an oxygen-containing material which adds oxygen atom(s) to the compound being oxidized.


Parasite. An organism that spends all or part of its life in close association with another species, taking food from it but giving nothing in return. Ectoparasites live on the outside of their hosts, while endoparasites live inside the host's body.

Parasitism (adj. parasitic). A type of symbiosis in which one member depends on another for its nutrients, or other services.

Parenchyma.  A tissue composed of living, thin-walled cells that can continue to divide even when mature; parenchyma cells usually leave intercellular spaces between them.

Parthenogenic. Refers to organisms asexually reproduced or developed through parthenogenesis.

Parthenogenesis. Reproduction without fertilisation (asexual); common in some mites,  insects and nematodes.

Pathogen (adj. pathogenic).  A disease-causing organism or agent.

Pedicel. A tiny stalk; the support of a single flower.

Peduncle. A primary flower stalk, supporting either a cluster or a solitary flower.

Periderm.  The outer layers of tissue of woody roots and stems, consisting of the cork cambium and the tissues produced by it.

Perithecium (pl. perithecia). flask-shaped, thin-walled fungal fruiting body (ascocarp) containing asci and ascospores, the latter being expelled or released through  a pore (ostiole) at the apex.

Pest.  Any organism that damages plants or plant products.

Petiole. Stalk of the leaf attached to a stem node.

pH. The measure of soil's acidity or alkalinity, measured on a scale of 1 to 14. Water is considered neutral at pH 7.

Pheromone. A chemical substance secreted by an animal or insect which when released externally in small amounts causes a specific reaction, such as stimulation to mate with or supply food to a receiving individual of the same species.

Phloem. Conductive vessels that transport food (carbohydrates) and waste products throughout the plant.

Photosynthesis. Process of manufacturing plant food  in which CO2 and H20 with light are combined to produce carbohydrates and O2.

Phylum (pl., phyla). A major division of the animal kingdom, containing various suborders and classes, etc.

Physiological disorder. Disorder due to physiological stresses caused by factors such as water, nutrition and temperature. 

Phytoalexin. A substance produced by higher plants which is toxic or inhibits the growth of microorganisms, especially phytopathogenic fungi such as Fusarium oxysporium and Ceratocystis fimbriata, and can be harmful for the host plant itself. 

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

Phytotoxic. Poisonous to plants.

Pigment. A coloured compound, such as chlorophyll, in the cells of plants or fungi.

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Small, depressed or sunken area in the leaf or any plant part. 

Polyphagous. Feeding on many different kinds of food.

Potyvirus (Siglum of potato virus Y). Member of a large group of plant viruses with flexuous particles containing a single molecule of linear RNA, most of which are transmitted by aphids in a noncirculative manner.

Predator. An insect that attacks and feeds on other insects, usually smaller and weaker than itself.

Prey. The insect on which a predator feeds.

Protonymph. A second instar of a mite.

Proximal. Concerning the basal part of an appendage - nearest to the point of attachment.

Pubescent. Covered with short, soft hair.

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Leaf surface contracting into wrinkles or bulges; showing an uneven bumpy appearance.


Mark or small dots made by insects on the leaf or any plant surface by piercing or pricking it.

Pungent. Unpleasantly sharp smell or taste.

Pupa. (pl., pupae).

The stage between larva and adult in insect with a complete metamorphosis such as butterflies and beetles. It is a non- feeding and usually inactive stage.

Pupate. To turn into and exist as a pupa.

Pycnidiospore. Pycnidium produced within a conidium.

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


Resistant. Possessing properties that prevent or impede disease development (see susceptible).

Reduviid. Any one of a group of winged insects (Reduviidae) whose mouthparts - adapted for piercing and sucking - take the form of a long proboscis that is tucked beneath the head when not in use.

Rhizobia. Bacteria in a symbiotic relationship with leguminous plants that results in nitrogen fixation.

Rhizosphere. Microenvironment in the soil, immediately around plant roots.

Roguing. Removing inferior, diseased or off-type plants.

Root exudates.  The various compounds that leak from growing and expanding sections of roots as well as from broken cells at exit points of lateral roots

Rosetting. A disease symptom characterized by short, bunchy growth habit due to shortened internodes and no comparable reduction in leaf size.

Rot. The discolouration, and often disintegration or breakdown of a succulent plant tissue as a result of fungal or bacterial infection.

Rugose. Wrinkled, roughened appearance of plant or plant part.


Saccate.  Having a pouch- or sac-like shape.

Salinity. Refers to an excess of salts in the soil which causes leaves to scorch and turn yellow and does great harm to many plants.

Sanitation. Disease or pest management activity to reduce spread of pathogens and pests such as  destruction or removal of infected and infested plants or plant parts; decontamination of tools, equipment, containers, work space, hands, etc.

Saprophytic. Living on dead or decaying organic matter.

Scarabaeiform.  A grub-like larva having a thick, soft body with a well-developed head and strong thoracic legs but with no legs on the hind region: often permanently curved into a C.

Sclerotium (pl.. sclerotia). A mass of hard, frequently rounded usually dark pigmented hyphal cells capable of being dormant for a long period of time and germinating under favourable conditions  to produce stroma, fruiting body, mycelium, or conidiophores.

Scorching. The drying and browning of leaf usually caused by unfavourable environmental conditions and some pests.

Secondary infection. Infection resulting from the spread of infectious material previously produced by another pathogen.

Seedbed. The bed on which storage roots (also referred to as seeds) are planted and from which storage roots sprouts are obtained for planting or for further multiplication.

Seedling.  In sweetpotato, it refers to the grown storage sprouts.

Senescence. Degeneration due to maturation, disease or disorder leading to death of plant or plant parts.

Septate. Having membrane or cross wall.

Septum (pl. septa). A cross wall in a hypha or spore;  thin partition or membrane that divides two cavities or soft masses of tissue in an organism

Seta. A bristle, or stout hair.

Shrivelled. Shrunken and wrinkled, often by drying.

Shot-hole .   Presence of round holes on  leaf surface caused by insects; symptom in which small lesions fall out of leaves, giving the leaf the appearance of being hit by buckshot.

Sign. Visible indication of disease such as the pathogen or its parts like spores, mycelia, hyphae. indication of disease from direct observation of a pathogen or its parts (see symptom).

Silaging. Storing and fermenting green plants in a silo.

Silica. A white or colourless crystalline compound, SiO2, occurring abundantly as quartz, sand, flint, agate, and many other minerals and used to manufacture a wide variety of materials, especially glass and concrete.

Siliceous. Containing, resembling, relating to, or consisting of silica.

Skeletonise. To remove tissue between leaf veins, having the network of veins intact.

Soil drench.  Application of a solution or suspension of a chemical to the soil, especially pesticides to control soilborne pathogens.

Soilborne.  Carried on or beneath the soil surface.

Solarization.  It is a non chemical control method against some diseases such as Fusarium wilt. It uses calorific energy irradiated by the sun. The objective is to increase the soil temperature up to levels that are lethal or sub-lethal to several soil pathogens. It is done by covering the wet soil with a transparent plastic sheet for 2,3 or more weeks as necessary, during the hottest part of the year. The temperature under the plastic increases to more than 50oC, which is the temperature that destroys fungi and nematode structures present in the soil, i.e mycelium, conidia, chlamydospores, sclerotia, nematode cysts, etc. This method has been found efficient  up to depth of 20 cm  from the soil surface.

Sooty mould. Black fungus that develops on sweetpotato leaf surface due to the presence of honeydew excreted by aphids and whiteflies, which may become so dense that it interferes with metabolism of the plant.

Sorus (pl. sori). Compact fruiting structure, especially the spore mass in rust and smut fungi.

Species. The basic unit of living things, consisting of a group of individuals which all look more or less alike and which can all breed with each other to produce another generation of similar creatures.

Spider. Any of numerous arachnids of the order Araneae, having a body divided into a cephalothorax bearing eight legs, two poison fangs, and two feelers and an unsegmented abdomen bearing several spinnerets that produce the silk used to make nests, cocoons, or webs for trapping insects.

Sporangiophore. A differentiated hypha  bearing sporangium.

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

Sporangiospore. Spores that develop in a sporangium.

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

Sporocarp. A fruit body that produces spores.

Sporodochium (pl. sporodochia). A cluster of conidiophores that arises from a stroma or mass of hyphae.

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A distinct colour or texture or marked part of a surface as on leaves, petioles, and stems, usually round or less elongated than strips or streaks caused by diseases, pests, disorders or stresses; more defined than mottling;  can interchangeably used with lesion when referring to brown, black or dead spot. For example:

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A shoot of a plant, as from a germinating seed or storage root.

Stage. A distinct, sharply differentiated period in the development of an insect,  e.g., egg stage, larval stage, pupal stage, adult stage;  r plant, e.g seedling, vegetative, reproductive stages.

Stem. The vascularized above-ground supportive portion of a plant, and below-ground structures with the same anatomy and development.

Sterilization (adj. sterilised). The total destruction of living organisms by various means, including heat, chemicals or irradiation.

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Series of small dots or speckles in which chlorophyll is absent.

Storage root. The starchy, edible roots of sweetpotato, sometimes referred to as tubers.

Stroma. A compact mass of vegetative tissue, sometimes intermixed with host tissue, often bearing sporocarps either within or upon its surface.

Stunting. A reduction in height of a plant resulting from a progressive reduction in the length of successive internodes or a decrease in internode number.

Stylospore. Elongated pycnidiospore.

Suberin.  Water-impermeable, waxy substance associated with corky tissues in or on plant parts.

Susceptible.  Lacking the inherent ability to resist disease or attack by a given pathogen; not immune; prone to develop disease when infected by a pathogen.

Symbiosis. A relationship in which two dissimilar organisms live in close association with each other.  Sometimes a symbiotic relationship is good for both species, or one species benefits more than the other, and in other cases neither species gains anything from the relationship.

Symptom. Manifested reaction of plant to a pests, pathogens or disorder e.g. yellowing of leaves, formation of galls, leaf spots, wilting, etc.

Systemic.  Pertaining to a disease in which the pathogen (or a single infection) spreads generally throughout the plant;may also pertain to chemicals that spread internally through the plant.


Tachinid fly.  Common name for any of the flies of the family Tachinidae, which parasitise caterpillars, beetles, grasshoppers, and other insects. Tachinid flies are generally small (about the size of houseflies), often bristly, and sometimes brilliantly coloured.

Tap root. primary root that grows vertically downward and from which smaller lateral roots branch.

Thallus. Vegetative body of a fungus.

Thatch. Tightly intertwined layer of plant litter from accumulations of undecomposed or partially decomposed plant residues.

Thorax. Insect body part between the head and abdomen.

Tillage.  The process of turning or stirring the soil.

Thinning. Removal of young plants or seedlings to provide bigger space for others to develop.

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

Toxicity. (nutrient). Occurs when nutrient concentration exceeds the critical concentration and becomes toxic to the plant.

Totipotency. The potential, throughout life, to express the full behavioural repertoire of the population (even if never actually expressed), and the ability to produce offspring like oneself, exhibiting the full behavioural repertoire of the population, without help.

Transpiration. Loss of water from plants through leaf pores in the form of water vapour.

Tropical. Occurring in the Tropics.

Tropics. Region of the earth's surface lying between either of two parallels of latitude on the earth, one 23°27 north of the equator and the other 23°27 south of the equator, representing the points farthest north and south at which the sun can shine directly overhead and constituting the boundaries of the Torrid Zone.


Upright growth. Erect  plant habit usually accompanied by shortening of internodes and sometimes, reduction in leaf size giving the dense or compact appearance.


Vacuole. Generally spherical organelle within a plant cell bound by a membrane and containing dissolved materials such as metabolic precursors, storage materials, or waste products.

VAM.(vesicular-arbuscular mycorrhiza). Mutual symbioses between the roots of most plants and fungi in the order Glomales (Zygomycetes).

Vascular. Refers to a plant's circulatory system, which consists of, or relates to, the specialized conducting tissues of plants-xylem and phloem, which circulates sap.

Vector. A living organism (e.g., insect, mite, bird, higher animal, nematode, parasitic plant, human) able to carry and transmit a pathogen and disseminate disease.

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

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Refers to the veins, eg. veinal chlorosis means loss of chlorophyll on the veins.

Vein clearing.   Disappearance of green colour in or around leaf veins; a symptom of virus-infected leaves in which veinal tissue is lighter green than that of healthy plants.

Ventral. On or concerning the abdomen or front or lower surface of an insect or animal body.

Vine twining. Twisting or coiling of vine around a central axis.

Virulence. The degree of ability of an organism to cause disease; degree or measure of pathogenicity; relative capacity to cause disease

Virus. An infectious, simple, submicroscopic particle composed of a protein capsule and a nucleic acid core, which is dependent on a host organism for replication  and not typically considered a living organism.


Walling-off.  Separation of diseased from healthy tissues by barrier tissues produced by a diseased plant.

Water-soaked.   Describing disease symptom of plants or lesions that appear wet, dark, and usually sunken and translucent.

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A reduction in plant rigidity and freshness resulting to drooping of  leaves and stems due to water stress  (i.e. inadequate water supply or excessive water loss).

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Formation of small furrow-like creases, depression or ridges; puckered appearance.


Xylem.  Conductive vessels that transport water and absorbed nutrients from roots to other tissues.


Yellowing.  A symptom characterized by chlorosis or loss of the green pigment, chlorophyll.



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Compiled by: Vilma Amante