Glossary

Compiled by Catherine F. George.

ACERVULUS (ah-sir-vu-tus) One of many types of fruiting bodies produced by fungi. It is a shallow, saucer-shaped, depressed structure consisting of a layer of stalk-like filaments (called conidiophores) that bear at their tips nonsexual spores (conidia) in a cushion-like mass. As the acervulus expands it ruptures the cell layers of the host plant, thus exposing its surface and permitting the spores to be set free. Plural: ACERVULL AECIUM (ee-see-um) A cuplike spore-producing structure developed by rust fungi. The spores produced in it (AECIOSPORES) can infect the same host on which they are formed but generally infect a different, unrelated one for example, the aeciospores of stem rust of wheat are formed on barberry and carry the infection to wheat.

AGAR A gelatin-like substance extracted from a seaweed. It is an ingredient used in making culture media to study the growth characteristics of micro-organisms.

ALLELOMORPH (a-lel-o-morf) Either of a pair of contrasting genes, or characters, such as roughness and smoothness, occupying the corresponding position in a pair of chromosomes. Adjective: ALLELIC, ALLELOMORPHIC; noun: ALLELOMORPHISM.

ALTERNATE HOST One of two kinds of plants upon which a parasitic fungus must develop to complete its life cycle. For example: The fungus that causes black stem rust of wheat parasitizes wheat and barberry and if deprived of either host cannot complete its life cycle. An aid in the control of rust on wheat, therefore, is to eradicate all barberry bushes in the locality.

AMPHIDIPLOID (am-fe-dip-loid) A combination resulting from the hybrization of two Species that contains the total chromosome complement all the characteristics of both parents.

ANTIBIOSIS (an-te-by-o-sis) Antagonism between two organisms, particularly microorganisms in soil, to the detriment of one of them. Antibiosis is used to control some soil fungi (such as the one that causes Texas root rot) by adding to the soil organic materials that encourage the growth of the antibiotic organisms at the expense of the pathogen.

ANTIBODY A chemical substance in the host that opposes the action of parasites, their products, or foreign materials.

ANTHRACNOSE Any disease caused by fungi that produce nonsexual spores in the type of fruiting body called an acervulus. Anthracnose usually is characterized by ulcer-like areas on the host.

APOTHECIUM (ap-o-thee-see-um) A disk-, saucer-, or cup-shaped fungus structure whose inner surface is lined with saclike membranes called asci, which contain spores called ascospores. Apothecia are found seated on or in the host or raised on a stalk. Some apothecia are barely visible to the eye; others are several inches in length or diameter. Usually they are more or less fleshy. The ascospores sometimes are set free by simultaneous explosion of the asci within the apothecium.

APPRESSORIUM (ap-re-sor-e-um) A sucker-like structure, usually disk-shaped, at the tip of a filament (hyphae) of some parasitic fungi by which the fungus adheres to the host plant. A peg, formed at the center of the appressorium, penetrates the host tissue.

ASCOMYCETES (ass-ko-my-see-teez) One of the major groups of fungi, characterized by the production of spores within an oval or tubular membranous sac called an ASCUS. The cells of the ascus divide to form the spores (usually eight), which are called ASCOSPORES. The asci (ass-see) of some fungi form a layer over the surface of a part of the host plant. Asci of other fungi are contained in fruiting bodies, of which there are two types perithecia and apothecia. Yeasts, molds, mildews, and truffles belong to the group and may be referred to as ascomycetes (ass-comy-seetz).

BACTERIOPHAGE A viruslike bacteria-destroying agent.

BACTERIUM A one-celled, microscopic organism which is a low form of plant life. The cell, which may be spherical (coccus type), rod-shaped (bacillus type), or spiral and cylindrical (spirillum type), may occur singly or in colonies or long chains, but each is considered an individual unit. Some have tiny filaments (flagella) that enable them to swim through a liquid. Bacteria are widely distributed in air, water, soil, bodies of living animals and plants, and dead organic matter. Lacking the green coloring matter, chlorophyll, they cannot manufacture their own food from carbon dioxide and water and must get it already prepared from other sources. Some live off dead matter and keep the earth from becoming a junk yard of plant and animal remains. Many live in the bodies of animals or in plants and thereby cause disease. The ones that cause plant diseases are usually of the rod-shaped type. They enter plants through a natural opening, such as a water pore, or through a wound. Once inside they multiply simply by dividing in two, and migrate among the cells of the plant. They may kill the cells or cause cancerous development of them.

BASIDIOMYCETES (ba-sid-i-o-my-see-teez) One of the major groups of higher fungi characterized by the production of sexual spores (BASIDIOSPORES) on a club-shaped filament called the EASIDIUM. Typically four basidiospores are formed on each basidium. Except for that characteristic, the fungi belonging to the group (such as rusts, smuts, and mushrooms) differ widely in structure and habits. In rust and smut fungi the basidium is called the promycelium and the basidiospores, the sporidia. A member of the group may be referred to as a basidiomycete (ba-sid-i-o-myseet) .

BIOTYPE A group of micro-organisms that have the same genetic characteristics; a subdivision of a race of fungi. See PHYSIOLOGICAL RACE.

BLASTING Causing failure to produce fruit or seeds.

BLIGHT A general term used to describe symptoms of plant disease which may include spotting, sudden wilting, or death of leaves, flowers, stems, or entire plants.

BORDEAUX 4-2-100 The figures following the name of this fungicide indicate the amounts of copper sulfate, hydrated lime, and water to be mixed. In this case, 4 pounds of copper sulfate and 2 pounds of lime in Ion gallons of water.

CAEOMA (see-oh-ma) A spore-producing structure of rust fungi similar to an aecium but commonly surrounded with fungus filaments rather than a definite wall; also a genus of the rust fungi.

CALYX (kay-liks) The outer group of floral leaves of a plant, often smaller and green in color as contrasted to the inner, more showy part, the corolla.

CAMBIUM LAYER A soft layer, strip, or cylinder of living cells which divide to form new tissues of the plant. The layer ordinarily extends over the plant body except at the growing tips.

CANKER A definite diseased area, usually on woody stems.

CARRIER A plant or animal bearing internally an infectious agent of disease, although it shows no marked symptoms of it. A carrier plant can be a source of infection to other plants or animals. An insect contaminated externally with an infectious agent is sometimes called a carrier.

CAUSAL ORGANISM The organism that produces a given disease.

CELL The structural and functional unit of all plant and animal life. It consists of a small mass of protoplasm, the substance which constitutes living matter, and a denser smaller body, the nucleus, and is surrounded by a membranous tissue, the cell membrane or cell wall. Living organisms may have one cell (bacteria) or billions (man).

CENTIGRADE THERMOMETER A thermometer on the scale of which the interval between the freezing and boiling points of water is divided into ion parts or degrees. To change degrees centigrade to degrees Fahrenheit multiply by nine-fifths and add 32.

CERTIFICATION OF SEED Seed production and marketing under control to maintain varietal purity and freedom from seed-borne pests.

CHEMOTHERAPY (kem-o-ther-a-pee) The treatment of disease by chemicals that work internally.

CHLAMYDOSPORE (klam-e-doe-spore) A rounded, nonsexual spore (formed by direct transformation of certain cells of a fungus filament or of an entire filament) which has a thick wall that favors its survival in soil or plant debris.

CHLOROPHYLL The green compound found in leaves and other plant parts by means of which the plant converts water and carbon dioxide of the air into food through the energy of the sunlight in a process called photosynthesis.

CITLOROSIS Yellowness of normally green tissues due to partial failure of chlorophyll to develop. Many diseases cause chlorosir, and frequently the pattern of the chlorotic area helps diagnose the disease.

CLEISTOTHECIUM (kly-sto-thee-see-um) A minute, black fruiting body of some fungi consisting of a surrounding wall completely enclosing one or more saclike membranes (asci) in which spores (ascospores) are produced. Under pressure of the developing asci the cleistothecium bursts, liberating the ascospores by forcible discharge.

CLONE A group of plants derived from a single plant by means of vegetative propagation such as the rooting of cuttings or slips, budding, or grafting. Every member of a clone has the same heredity, so that under uniform environment a group of plants from a single clone is quite uniform. Compare Strain.

COLLENCHYMA (ko-leng-ki-ma) The tissue in elongating soft stems and certain other parts of plants which helps support the plant.

CONIDIUM (ko-nid-e-um) A fungus spore formed by being pinched off or cut off from the tip of a specialized, erect, aerial filament (hypha) called a CONIDIOPHORE. Conidia have various shapes and sizes. They are sometimes called summer spores because they are produced in abundance during the growing season. Usually they are wind-borne, but some are washed away by rain or drop to the ground where they may be moved about by man, animals, machinery, or water.

COREMIUM (ko-ree-me-um) A cluster of erect fungus filaments (hyphae) which are joined together to form a column and which bear nonsexual spores (conidia).

CORIACEOUS (ko-ree-a-shus) Tough, leather-like.

COROLLA (ko-rol-a) The petals of a flower collectively; the inner part of the floral leaves of the plant, usually more delicate and brightly colored than the outer part, the calyx.

CORTEX The portion of the stem or root of vascular plants external to the vascular tissue. Adjective: CORTICAL.