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On-Line Glossary: A

Each entry consists of a term (in bold), a definition of the term, and a number in parentheses (0) indicating the source of the definition. Clicking on the speaker icon will give you the pronunciation of the term. (Be sure to close the window for the sound player after each use.) The pencil icon will give you a drawing, and the camera icon will give you a photograph.


abaxial. Directed away from the stem of a plant; pertaining to the lower surface of a leaf. (5)

abiotic. Non-living; of non-biological origin. (16)

abscission. Of plants: The shedding of leaves or other parts as the result of physical weakness in a specialized layer of cells (abscission layer) that develops at the base. (21)

acerose. Needle-shaped, like pine needles. (17)

acervulus. A mass of closely clustered conidiophores and conidia not covered by fungal tissue, initially subcuticular or subepidermal but eventually exposed. (pl. acervuli) (15)

acropetal. Describes the development of structures (such as spores) in succession from the base towards the apex. (20)

actinomycete. Any member of the order Actinomycetales; the name is often used to refer specifically to those species which form mycelium. (pl. actinomycetes). (16)

actinomycetes. (literally "ray fungi") filamentous bacteria that have sometimes been classified as Fungi Imperfecti. Actinomycetes typically are saprobes (especially in soil) but a few are pathogenic to man, animals, and plants. (7)

acute. 1. Developing suddenly, severe (with reference to disease symptoms). 2. Less than 90 degrees (with reference to an angle). (5)

acute symptoms. See shock symptoms.

adanal. (Nematology) Pertaining to a bursa that does not envelop the entire tail. (14)

adaxial. Directed toward the stem of a plant; pertaining to the upper surface of a leaf. (5)

adjuvant. Material added to improve some chemical or physical property (e.g., of a plant protectant) or a biological property (e.g., to improve antibody response to an antigen). (8)

adnate. (Mycology) Of gills or tubes broadly attached to the stipe; attached by nearly the entire width of the gills or layer of tubes. (17)

aecidiospore. See aeciospore.

aecidium. An aecium with a cup-like outer wall. (pl. aecidia). (16)

aeciospore. A dikaryotic "transfer" spore of the Uredinales, formed in an aecium on the alternate host in macrocyclic rusts and infecting only the primary host; spores of Stage I in heteroecious or autoecious rusts. (12)

aecium. In the Uredinales the first sorus that is formed after plasmogamy and bears binucleate aeciospores (Stage I heteroecious or autoecious rusts). (Pl. aecia.) (15)

aerobe. An organism that requires free oxygen for respiration. (15)

aerobic. With the qualities of an aerobe. (15)

agar. Mixture of polysaccharides derived from red algae that forms a gel at temperatures below about 40C. Used as a support medium, when supplemented by appropriate buffers and/or nutrients and other ingredients, for the production of microbial cultures, overlaying tissue culture cells, electrophoresis, etc. (10)

agarose. One of the constituents of agar. Often used in preference to agar because it gels at a lower temperature and does not contain the inhibitors of virus growth frequently present in agar. It is also used widely in gel electrophoresis because it has a more uniform pore size than that of agar. (10)

agent of disease. An organism or abiotic factor that causes disease; a pathogen. (21)

agent of inoculation. That which transports inoculum from its source to or into the infection court (e.g., wind, splashing rain, insects, humans). (20)

agglutination. The formation of insoluble aggregates following the combination of antibodies with cells or other particulate antigens or with soluble antigens bound to cells or other particles or following the combination of soluble (or particulate) antigens with cell-bound or particle-bound antibodies. (16)

aggressiveness. Of a plant pathogen: relative ability to colonize and cause damage to plants. (21) See also virulence. (Note: The Federation of British Plant Pathologists, now the British Society for Plant Pathology, has rejected this term and considered it to be synonymous with pathogenicity.) (8)

alae. (Nematology) Expansions or projections formed by a longitudinal thickening of the cuticle of a nematode. Cervical alae are confined to the anterior region of nematodes parasitic in animals. Caudal alae occur in the posterior region of males in a number of genera. Longitudinal alae, usually four, extend the length of the body sublaterally. (14)

allantoid. Of spores: sausage-shaped; somewhat curved, with rounded ends. (17)

allele. (allelomorph). Any of one or more alternative forms of a given gene; both (or all) alleles of a given gene are concerned with the same trait or characteristic, but a particular allele codes for a product qualitatively and/or quantitatively different from that coded by other alleles of that gene. (16)

allelomorph. See allele.

alternate host. One of two kinds of plants on which a parasitic fungus (e.g., a rust) must develop to complete its life cycle. . (16)

alternative host. A plant other than the main host that a parasite can colonize; alternative hosts are not required for completion of the developmental cycle of the parasite. (20)

amerospore. A non-septate spore. (12)

amerosporous. Having one-celled spores. (17)

amphid. In nematodes: A chemosensory organ, occurring laterally in pairs, located in the anterior region. Sometimes called lateral organs. (14)

amphidelphic. In nematodes: Having two ovaries, one directed anteriorly and the other posteriorly. (14)

amphigynous. In fungi: Having an antheridium through which the oogonial initial grows. (23)

amphimictic. In nematodes: 1. Reproduction in which sperm and eggs come from separate individuals (cross-fertilization). 2. Capable of interbreeding freely and of producing fertile offspring. (18)

amphiospore. Urediniospore with thickened walls and capable of hibernating. (20)

amphispore. Amphiospore. (20)

amplification. Production of multiple copies of a DNA sequence, either in vivo or in vitro, starting with one or a few copies. (19)

ampulliform. Flask-like in form. (7)

amyloid. Of spore walls, spore ornamentation, hyphal walls, ascus tips, etc.: Staining blue or grayish to blackish-violet in Melzer's reagent, presumably because of the presence of starch or a starch-like compound. (17)

anaerobic. Not requiring free, molecular oxygen for respiration. (15)

anamorph. An asexual (usually conidial) stage in the life cycle of a fungus. (15)

anastomosis. (= hyphal fusion). Fusion of somatic hyphae; characteristic of most Dikaryomycota. (Pl. anastomoses.) (12)

aneuploid. Chromosome constitution differing from the usual diploid constitution by loss or duplication of chromosomes or chromosomal segments. (13)

angiocarpous. Of basidium-producing organs: Hymenial surface at first exposed but later covered by an incurving pileus margin and/or excresences from the stipe. (7)

annule. Thickened interval between transverse striae in the cuticle of a nematode. (14)

annulus. A membraneous skirt surrounding the stipe of a hymenomycete or gasteromycete. (pl. annuli) (15)

antagonism. An ecological association between organisms in which one or more of the participants is harmed or has its activities limited. (15)

antagonist. An agent or substance that counteracts the action of another. (1)

antagonistic symbiosis. Parasitism; one organism of an association beefits at the expense of the other. (20)

antheridium. A male gametangium. (Pl. antheridia.) (16)

anthocyanescence. Having reddish-purple color in tissues that are normally green; often a symptom of plant disease appearing in the nearly dead margins around completely dead spots in green leaves. (20)

anthracnose. Any of various plant diseases, particularly those caused by fungi of the Melanconiales, in which discrete, dark-colored, necrotic lesions develop on the leaves, stems, and/or fruits. (16)

antibiosis. An association between two organisms that is detrimental to the vital activities of one of them. (20)

antibiotic. Substance used to inhibit the growth of micro-organisms, including bacteria and fungi. (10)

antibody. Any immunoglobulin molecule produced in direct response to an antigen and which can combine specifically, non-covalently, and reversibly with the antigen which elicited its formation. (16)

antigen. Molecule of carbohydrate or protein which stimulates the production of an antibody, with which it reacts specifically. (10)

antiserum. The serum from a vertebrate that has been exposed to an antigen and which contains antibodies that react specifically with the antigen. (Pl. antisera.) (10)

apiculate. Having an apical point or apiculus. (17)

apiculus. A short, sharp, but not stiff, point, usually as the bud of a spore. (Pl. apiculi.) (17)

apothecium. An ascus-bearing structure (ascocarp) in which the ascus-producing layer (hymenium) is not covered by fungal tissue at maturity. (Pl. apothecia.) (15)

appressorium. An enlargement on a hypha or germ tube that attaches itself to the host before penetration takes place. (Pl. appressoria.) (15)

arbuscule. Of vesicular-arbuscular mycorrhizae: a much-branched, microscopic haustorial structure of the fungal symbiont that forms within living cortical cells of the root. The interface of the arbuscule with the plant protoplast is a site of exchange of nutrients and growth-regulating chemicals. (21)

arcuate. Curved like a bow. (14)

areolated. Divided into small spaces or areolations; usually pertains to the cuticle of a nematode. (14)

areolation. A condition in which the transverse body annulation of a nematode traverses the lateral field. (14)

arthrospore. A spore resulting from the fragmentation of a hypha, as in the conidial stage of many Basidiomycetes. (17)

ascigerous. Of fungi: having asci. (21)

ascocarp. Ascospore-bearing, multicellular sporocarp formed by a member of the Ascomycotina. (15)

ascoconidium. A budded spore arising from an ascospore within an ascus. (15)

ascogenous hypha. The restricted dikaryophase of many Ascomycetes; a dikaryotic hypha that grows out from the fertilized ascogonium. (12)

ascogonium. In Ascomycetes: the female gametangium; it may be unicellular or multicellular, simple or complex in form. (Pl. ascogonia.) (16)

ascohymenial. Of, pertaining to, or having the characteristics of the Ascohymeniales. (17)

Ascohymeniales. Ascomycetes having asci (and paraphyses) developing as a hymenium and not in a preformed stroma. (7)

ascolocular. Of, pertaining to, or having the characteristics of the Loculoascomycetes, the loculate Ascomycetes. (17)

ascoma. Synonymous with ascocarp. (Pl. ascomata.) (16)

ascomycete. Fungus of the subdivision Ascomycotina. . (In some taxonomic schemes these fungi form the class Ascomycetes.) (16)

Ascomycotina. A subdivision of fungi characterized by the formation of sexually derived spores (ascospores) in asci. (Ascomycetes, Ascomycota) (16)

ascophore. A structure bearing asci (e.g., an ascus-producing hypha). (17)

ascospore. A spore borne in an ascus. (15)

ascostroma. A fructification of the Ascomycetes consisting of an undifferentiated mass of tissue or stroma on or in which the asci are developed. (Pl. ascostromata.) (17)

ascus. A cell that is the site of meiosis and in which endogenous spores (usually meiospores but sometimes also ascoconidia) are formed. (Pl. asci.) (15)

aseptate. Lacking septa (nonseptate). (16)

asporogenous. Not capable of forming spores. (16)

autoecious. Capable of completing a life cycle on one host.

autotrophic. Capable of growth independent of outside sources of nutrients or growth factors. (20)

auxotroph. A strain of microorganism lacking the ability to synthesize one or more essential growth factors. (16)

avirulent. Not exhibiting virulence; nonpathogenic. (5)

avoidance. Principle of plant disease control marked by deliberate actions to take advantage of environmental factors and time unfavorable for disease development. (20)

axial. Belonging to, around, in the direction of, or along an axis. (14)

azygospore. A parthenogenetic zygospore; formed by some vesicular-arbuscular mycorrhizal fungi (family Endogonaceae). (21)

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