Glossary

Aggressiveness - to maintain self in nature; disease-causing capacity in nature; a component (with virulence) in parasitic fitness; a concept similar to parasitic fitness. See Shaner et al. (1992), Annual Review Phytopathology 30:47-66 for further discussion of this concept.

Allantoid- curved spores, sausage-like in form.

Anastomosis- of hyphae and exchange of their contents.

Anthesis-, evident in cereals and grasses by extrusion of the anthers.

Apical meristem- at the tip of a shoot that function in cell division and differentiation.

Apiculus- short projection on the end of a spore by which it was fixed to the sterigma.

Appressorium- swelling on a germ tube or hypha for attachment in early stages of host penetration.

Areolate- divide into small areas by margins that differ in color, texture, or structure.

Avirulent- of a pathogen to overcome host resistance.

Axenic culture- growing system for one microorganism free of others.

Basidiospore- propagative cell produced on a basidium after meiosis. It contains one or more haploid nuclei.

Bipolar- form of heterothallism involving only one pair of alleles at a single locus that controls compatibility .

Biotype- subdivision of physiologic race the individuals of which have similar genetic makeup; of bacteria, a subdivision of species distinguished by some physiological characteristic.

Bunt- smut fungus that sporulates only in the ovaries. Also, the disease caused by these fungi.

Bunt ball- of smut fungi that replaces the kernel.

Caryopsis- seed of a grass or cereal.

Centipoise- standard of viscosity equal to 0.01 poise, the c.g.s. unit of viscosity. Water at 20oC has a viscosity of 1.002 centipoise or 0.002 poise.

Coleoptile- protective sheath surrounding the shoot in cereals and grasses.

Common bunt- smut disease caused by Tilletia tritici or T. laevis that infects seedlings.

Control of disease- check or reduce the presence of or the effects of plant disease.

Cotyledon- first seedling leaf or leaves.

Cultivar- cultivated variety as opposed to a botanical (taxonomic) variety.

Differential host- line or cultivar that is susceptible to some pathogen isolates, but resistant to other isolates.

Differential set- group of genotypes used for distinguishing physiologic races that usually include a universal susceptible and a universal resistant genotype among the genotypes that differ in reactions to the pathogen collections.

Dikaryon- fungal cell containing two genetically distinct and sexually compatible haploid nuclei.

Dikaryophase- of three phases in the life cycle characterized by cells with two haploid nuclei of opposite mating type.

Diploid-&A nucleus carrying two sets of chromosomes.

Diplophase- of three phases in the life cycle characterized by diploid nuclei.

Disease- abnormal physiological reaction of a plant to a pathogen, often accompanied by symptoms and altered morphology and/or anatomy.

Disease cycle- chain of events involved in disease development, including the stages of pathogen development and effects of the disease on the host.

Disomic- two sets of homologous chromosomes or genes.

Dissemination- and spread of fungus spores from the site of production.

Dominant- allele that masks the phenotypic effect of another allele of the same gene. The phenotypic effect is the same in the heterozygous as in the homozygous condition.

Dormant- due to reduced physiological activity.

Dwarf bunt- smut disease caused by Tilletia controversa that infects seedlings and severely stunts tillers.

Endosperm- tissue surrounding the embryo in the seed that provides nutrition to the embryo.

Environment- physical and biological surroundings of a species or group of species.

Exospore- outer covering of a spore.

Filiforme--like structure.

Flag leaf- uppermost leaf on the stem.

Flag smut- smut disease that affects primarily leaves and culms, as in Urocystis agropyri.

Floret- flower in the spikelet of a cereal plant.

Formae speciales- subdivision of a pathogen species based primarily on the host genera that are attacked.

Fungicide- chemical that is toxic to fungi.

Fungistatic- chemical that inhibits the growth of fungi without killing.

Fungus- undifferentiated plant lacking chlorophyll and conductive tissues.

Funiculus- slender stalk of an ovule or seed.

Fusiforme--like in shape.

Gene- hereditary unit on a chromosome which determines or conditions one or more characteristics.

Gene-for-gene relationship- specific interaction of a host and a pathogen that is conditioned by complimentary genes of host and pathogen.

Germicide- chemical that kills micro-organisms, especially pathogens.

Germination- initiation of growth from a resting propagule.

Glume- bract at the base of a spikelet of a cereal or grass.

Haploid- a single set of chromosomes.

Haplophase- of three phases in the life cycle characterized by nuclei that are haploid.

Haplont- organism having haploid somatic nuclei.

H-body- structure formed by the fusion of sporidia.

Heterobasidiomycete- that have basidia of different form and that are usually divided by septa.

Heterothallic- different genotypes or mating types are required for sexual reproduction.

Homothallic- haploid nucleus can give rise to a mycelium that is capable of sexual reproduction.

Host range- genera and species that are susceptible to a pathogen; resistant or immune genera or species are not usually included among hosts.

Hypersensitive reaction- response to infection characterized by rapid death of cells and tissues that prevents further growth of the pathogen.

Hypocotyl- part of the stem below the cotyledons in the embryo.

Immune- from infection by a pathogen.

Incompatible reaction-/pathogen response to infection that results in immune or resistant reactions.

Infect- establish a pathogenic relationship with a host plant.

Inoculate- introduce pathogen propagules onto or into a host or culture for the purpose of producing infection or for growing the pathogen in culture.

Inoculum- of microorganisms used for inoculation.

Isolate- spore or culture of a microorganism, and derived cultures, that are separated from others.

Karnal bunt- bunt disease that infects immature seeds, caused by Tilletia indica; named for the town of Karnal, India.

Karyogamy- union and interchange of nuclei after cytoplasmic fusion, the fusion of two compatible haploid nuclei into one diploid nucleus.

Latent period- time between inoculation and appearance of symptoms and/or spore production.

Lemma- lower enclosing bract of the flower in cereals and grasses.

Linkage- association of genes located on the same chromosome.

Lodicules- small scale-like structures below the ovary in cereals and grasses that swell up at flowering and open the bracts.

Loose smutA- smut disease caused by Ustilago tritici that infects ovaries only.

Mating type- subdivision of a microorganism on the basis of mating behavior.

Matrix potential- absorption and capillary forces that bind water to plant and soil constituents.

Meiosis- reduction division of chromosomes in a diploid nucleus that results in the formation of four haploid gametes.

Micron (µm)- unit of length equal to 0.001 mm.

Mitosis- division of a nucleus in which chromosomes are duplicated, giving rise to two daughter nuclei with the original chromosome complement.

Monogenic- one type of gene.

Monokaryon- individual having one nucleus per cell.

Monokaryotic- consisting of cells with single nuclei.

Monosomic- plant with one missing chromosome.

Morphological resistance- of plant disease by means of structural and anatomical features of plants.

Mycelium- mass of hyphae or the thallus of a fungus.

n- single set of chromosomes per nucleus; 2n- double set of chromosomes per nucleus; (n + n)- haploid nuclei of opposite mating type within a cell.

Nucellus- central portion of an ovule containing the embryo sac.

Ovary- female reproductive structure that contains the egg.

Palea- upper enclosing bract of the flower in cereals and grasses.

Partial resistance- expressed by reduced rate of infection, though symptom expression and macroscopic development of the pathogen are similar to those on a susceptible genotype; in smuts, infection occurs followed by some sporulation.

Pathogen- organism capable of causing disease.

Pathogenicity- to cause disease.

Pathotype- subdivision of a species with characteristic pathogenicity, especially host range, synonymous with formae speciales.

Pericarp- wall of a ripened ovary.

Physiological resistance- or reduction of plant disease development or severity due to physiological responses of the plant to the pathogen.

Physiologic race- population of individuals that are alike in morphology, but differ in their virulences on a set of differential cultivars or that differ in other cultural or physiological characteristics.

Physiologic specialization- process whereby isolates or races of microorganisms become differentiated in function, as in pathogenicity or ability to grow on specific media.

Plasmogamy- process of anastomosis of two cells with intermingling of their protoplasts and bringing haploid nuclei of opposite mating type into one cell.

Plumular bud- apical meristem.

Primary homothallism- nuclei are of the same genotype and sexual reproduction occurs without the intervention of another spore or thallas.

Promycelium- germ tube (basidium) of a ustilispore (teliospore) of a smut fungus.

Rachis- stem of the spike in cereals and grasses.

Recessive- allele that does not produce a phenotypic effect when heterozygous with the dominate allele, masking the effect of an allele by another allele of the same gene.

Resistance- genetic characteristic of a plant that prevents or reduces pathogen or disease development toward disease.

Reticulation- net-like appearance of the teliospore wall of smut fungi like Tilletia tritici.

Rogue- remove unwanted plants from a plot or field.

Scutellum- flat portion of the embryo of a cereal or grass, probably the cotyledon pressed against the endosperm.

Secondary homothallism- of nuclei of compatible mating types within a single spore and sexual reproduction occurs in cultures derived from the single spore.

Septum- wall of a hypha or other fungal structure.

Set of testers- as differential set.

Smut- disease characterized by masses of dark spores, caused by members of the Ustilaginales.

Solopathogen- isolate of a smut fungus with diploid sporidia due to failure of meiosis. The cultures are detected by infection caused by a single sporidium.

Sorus- compact spore bearing structure characteristic of smut fungi or other fungi.

Spike- inflorescence on an axis, or the head of cereals or grasses.

Spikelet- appendage of a spike that consists of florets and glumes.

Spore ball- structure made up of sori and peripheral cells, characteristic of flag smut fungi.

Sporidium- smut spore other than a ustilospore (teliospore).

Spring wheat- that does not require vernalization to grow and produce a crop; usually sown and harvested without interruption in the growth of the crop.

Stomata- openings in the epidermis of a plant that are surrounded by guard cells.

Subcrown internode- internode between the crown and the germinated seed.

Symptom- indication of disease in a plant.

Stubble- crop residue.

Substitution lines- stocks in which an entire chromosome has been replaced by an equivalent chromosome from another cultivar or species.

Teliospore- to ustilospore, a dikaryotic black resting spore, with two haploid nuclei (n + n), which become diploid (2 n) before germinating.

Teliosporogenesis- formation of teliospores.

Testa- hard outer covering of a seed.

Tetraploid- cell with four sets of chromosomes in the nucleus.

Tetrapola- form of heterothallism that involves two loci each with a pair of alleles that control compatibility.

Tiller- shoot or culm of a cereal or grass plant arising from a crown bud at the ground level.

Tilletiaceae- family of Ustilaginales the teliospores of which germinate by a promycelium (basidium) that bears terminal sporidia (basidiospores).

Transgressive segregation- pattern of inheritance in which some progeny have superior resistance to either parent and others have inferior resistance.

Trimethylamine- volatile chemical that causes the foul odor characteristic of bunt diseases.

Ustilaginaceae- family of Ustilaginales the teliospores of which germinate by a promycelium (basidium) that bears lateral sporidia (basidiospores) or branches.

Ustilaginales- of fungi, the smut fungi, consisting of the families Tilletiaceae and the Ustilaginaceae.

Ustilospore- resting spore of smut fungi that gives rise to the basidiospore. Analogous to teliospore.

Vacuum inoculation- of seeds or spikes in a vacuum that is suddenly released to bring inoculum and seed surfaces into close contact.

Vernalization- act of stimulating reproductive growth in a plant by subjecting seedlings to low temperatures away from light.

Virulence- specific ability of a pathogen to overcome host resistance.

Winter wheat- that requires vernalization, usually sown late in the fall and harvested the next growing season.