Agar – A gelatinous mixture of dried polysaccharides obtained from certain red algae and used to prepare semisolid culture media on which microorganisms such as fungi and bacteria are grown and studied.
Appressorium (pl. appressoria) – A swollen, thick-walled, or flattened terminal of a germ tube of a fungus that serves to attach to the host surface during the infection process.
Ascospore – A sexual spore formed inside an ascus following the union of two nuclei.
Ascus – A saclike cell where ascospores are formed during the process of meiosis.
Chlorosis – Yellowing or paling of normally green plant tissue resulting from destruction of chlorophyll. It may be due to disease or lack of nutrients.
Collar – A band between the leaf blade and sheath on the outside of a grass leaf.
Conidiophore – A hyphal cell or group of cells that bears conidia-producing (conidiogenous) cells.
Conidium (pl. conidia) – An asexual spore developing externally or liberated from a conidiogenous cell.
Cultivar – Group of closely related plants of common origin within a species that retain their distinguishing features when reproduced sexually or asexually.
Cytotoxic – toxic to a cell/s.
Diarrhea-inducing – Causing diarrhea, an intestinal disorder that results in abnormal frequency and fluidity of fecal evacuations.
Differentials – Special genotypes, cultivars, or lines of plants differing in susceptibility to a disease agent and enabling the identification of pathogen races based on distinctive symptoms produced on the differentials.
Erumpent – Projecting from or bursting through host tissue.
Feekes scale – One of several cereal development scales used in cereal research and agriculture. Feekes growth stages range from Feekes 1 (first leaf through coleoptile) to Feekes 11.4 (kernel hard, can no longer be dented by thumbnail).
Flag leaf – The last leaf to emerge on a wheat plant.
Gene – The basic unit of heredity in a living organism, made up of a segment of deoxyribonucleic acid (DNA).
Genotoxic – Toxic to a gene/s.
Genotype – The genetic makeup of an organism that influences the phenotype.
Germ tube – A hyphal thread that forms from a fungal spore wall and/or cytoplasm during germination of the spore.
Glume – One of the two sterile chaff-like bracts at the base of a grass spikelet.
Inoculum (pl. inocula) – Any part of a pathogen (e.g., a spore or vegetative structure) capable of causing disease.
Kernel – a whole seed grain.
Ligule – An outgrowth on a grass leaf from the upper and inner side of the leaf blade where it joins the sheath.
Line – A type of cultivar.
Meiosis – A two-stage cell division in a sexually reproducing organism that results in cells with half the chromosome number of the original cell.
Mitosis – Nuclear division in eukaryotic cells that conserves chromosome number by equally allocating replicated chromosomes to each daughter nucleus.
Mutagenic – Causing mutagenesis, the production of mutations.
Mutation – An abrupt change in a gene.
Mycelium (pl. mycelia) – Strands or mass of interwoven, tubular hyphae making up the vegetative body of a fungus.
Mycotoxin – Toxin produced by a fungus.
Necrosis – Death and disintegration of plant cells or parts of plants, usually resulting in browning or blackening of tissue.
Pathogen – An organism capable of causing disease in a particular host or range of hosts.
Pathotype – A variant of a given pathogenic species.
Phenotype – Visible or otherwise observable characteristics of an organism determined by its genotype and modified by the environment.
Physiologic race – Subdivision within a species of an organism, e.g. a fungus, whose members are alike in morphology but differ from other races in virulence or symptom expression on specific host genotytpes.
Potato dextrose agar – Agar containing extract from potatoes with added dextrose (glucose).
Precursor – A chemical that is transformed into another compound and therefore precedes that compound in the synthetic pathway.
Primary infection – Infection caused by primary inoculum.
Primary inoculum – Inoculum, usually from an overwintering source, that initially causes disease.
Pseudothecium – A (usually) dark fungal fruiting body in which asci are formed directly in a cavity within a stroma.
Race – A subcategory within a species distinguished by host cultivar specificity but not morphology, e.g. races can be distinguished by differing in virulence to cultivars of the same host species.
Residue – Something that remains after a part is removed, disposed of, or used; e.g., crop residue that remains after harvest.
Resistant – Possessing the ability to hinder or reduce the development of a pathogen or the damaging effects of other factors.
Secondary infection – Infection caused by secondary inoculum.
Secondary inoculum – Inoculum arising from primary or subsequent infections during the same growing season.
Spore – A one- to many-celled microscopic reproductive body of a fungus or bacterium that becomes free and can develop into a new fungus or bacterium.
Strobilurin fungicides – A class of fungicides named in recognition of a mushroom, Strobilurus tenacellus,which was the original source of the chemical that formed the basis of the chemistry of this group of fungicides.
Stroma – Compact mass of specialized vegetative hyphae.
Susceptible – Lacking the ability to hinder or reduce the development of a pathogen or the damaging effects of other factors.
Toxin – Poisonous secretion produced by a living organism.
Triazole fungicides – A class of fungicides characterized by having a five-membered ring of two carbon atoms and three nitrogen atoms and a common mode of action (inhibition of ergosterol biosynthesis).
V8 agar – Agar containing V8 vegetable juice.
Vesicle – A swollen hyphal cell.
Virulent – Having the ability to cause severe disease.
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