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macroconidium. The larger of two types of conidia formed by certain fungi. (Pl. macroconidia.) See microconidium. (16)

macrocyclic. Of rusts: The two primary spore stages are present (telial with teliospores and aecial with aeciospores). (8)

macroscopic. Visible to the unaided eye. (16)

mammillate. Digitate, with nipple-shaped protuberances. (14)

masked symptoms. Virus-induced plant symptoms that are absent under some environmental conditions but appear when the host is exposed to certain conditions of light and temperature. (2)

mechanical inoculation. Of plant viruses, a method of experimentally transmitting the pathogen from plant to plant; juice from diseased plants is rubbed on test-plant leaves that usually have been dusted with carborundum or some other abrasive material. (20)

medium. In microbiology: any liquid or solid preparation made specifically for the growth, storage, or transport of microorganisms or other types of cell. (Pl. media.)

median bulb. See metacorpus. (16)

medulla. Central part of an organ. (20)

meiosis. The process in which a eukaryotic nucleus divides into nuclei whose ploidy is lower than that of the parent nucleus (typically, haploid nuclei being formed from diploid nuclei) and in which recombination usually occurs. (16)

meiospore. A uninucleate, haploid spore arising directly by meiosis. (22)

messenger RNA. A chain of specific ribonucleotides that codes for a specific protein; template for the assembly of amino acids into protein; in cells mRNA is transcribed from DNA, but some RNA viruses function directly as mRNA. (16)

metabasidium. The cell in which meiosis occurs in members of the Basidiomycotina. (Pl. metabasidia.) (15)

metacorpus. The swollen posterior portion of the corpus; sometimes called the median bulb. (14)

metaplasia. Changed condition of a structure or organ; hyperplastic class of symptoms characterized by overdevelopment other than that due to hypertrophy or hyperplasia. (e.g., abnormal starch accumulation, virescence, etc.). (20)

microconidium. 1. A spermatium. 2. A small conidium. (Pl. microconidia.) See macroconidium. (16)

microcyclic. A life cycle in the rusts where one or more of the main spore stages, usually the aecial, is absent. (8)

micropyle. In nematodes: A minute opening in the membrane of an egg through which the spermatozoa enter. (14)

microsclerotium. A small clump of dark-colored, more or less thick-walled cells, each of which is viable; produced in culture and rarely in the xylem of host plants. (See sclerotium.) (Pl. microsclerotia.) (17)

microscopic. Very small; seen only with the aid of a microscope. (2)

mildew. A fungal disease of plants in which the mycelium and spores of the fungus are seen as a whitish growth on the host surface. (2)

minimal medium. A type of culture medium lacking specific growth factors; it does not support the growth of some or all auxotrophic strains of a given organism but permits the growth of prototrophic strains. (16)

mitosis. A sequence of cellular events that culminates in the division of a eukaryotic nucleus into two genetically similar or identical nuclei whose ploidy is the same as that of the parent nucleus. Mitosis occurs during asexual cell division. . (Pl. mitoses.) (16)

mitospore. A uninucleate, haploid or diploid spore arising by mitosis. (17)

Mitosporic fungi. See Deuteromycotina.

MLO. Mycoplasma-like organism. See phytoplasma.

mold. A downy fungal growth on a substratum, usually consisting of mycelium of a Hyphomycete or a Zygomycete. (15)

mollicute. A proposed trivial name for any member of the class Mollicutes. The use of this name could permit "mycoplasmas" to be used specifically for members of the genus Mycoplasma. (16)

molt. To cast off the cuticle. (14)

monocyclic. Of a disease or pathogen: Producing one generation of inoculum and one cycle of infection during a single growing season. (See polycyclic.) (3)

monodelphic. Of nematodes: Possessing one genital tube or ovary. (14)

monoecious. Having male and female reproductive organs on a single thallus. (15)

monogenic. Of nematodes: Producing offspring of only one sex. (14)

monogenic resistance. Resistance determined by a single gene. (5)

monokaryotic. Having one nucleus per cell. (16)

monophialide. See conidiophore. (5)

monotype. The sole species of a newly proposed genus. (16)

morphologic. Pertaining to form. (21)

mosaic. A common symptom induced in leaves by many plant virus infections in which there is a pattern of dark green, light green and sometimes chlorotic areas. This pattern is often associated with the distribution of veins in the leaf. In monocotyledonous leaves it shows as stripes. (10)

mottle. A diffuse form of the mosaic symptom in plant leaves in which the dark and light green are less sharply defined. This term is frequently used interchangeably with mosaic. (10)

mRNA. See messenger RNA. mucro. In nematodes: A stiff or sharp point abruptly terminating an organ. (14)

mucronate. In nematodes: Ending in a sharp point. (14)

mulch. A protective covering that is spread on the ground around plants to inhibit evaporation and weed growth, control soil temperature, enrich the soil, or prevent the dispersal of pathogens. It may be organic material such as leaves, peat, or wood chips, or inorganic material such as plastic sheeting. (1)

multicomponent virus. A virus in which the genome needed for full infection is divided between two or more particles (e.g., cowpea mosaic virus, brome mosaic virus, cucumber mosaic virus). (10)

multiline. A plant cultivar made up of a mixture of isolines differing in their genes for resistance to a particular pathogen. (Also multiline cultivar.) (16)

multiseptate. Having more than one septum. (7)

mummy. A dried, shrivelled fruit colonized by a fungus. (3)

muriform. Having bricklike cells in a wall with both longitudinal and transverse septa. (5)

mushroom. A fleshy fruiting body of a fungus, especially of a basidiomycete of the family Agaricaceae. (20)

mutant. Of an organism, population, gene, chromosome, etc.: Differing from the corresponding wild type by changes in one or more loci. (16)

mutation. A stable, heritable change in the nucleotide sequence of a genetic nucleic acid (DNA, or RNA in viruses, viroids, etc) typically resulting in the generation of a new allele and a new phenotype. (16)

mutualism. See symbiosis.

mycelium. A mass of hyphae, often used to denote all hyphae comprising a thallus. (Pl. mycelia.) (15)

mycology. The study of fungi. (20)

mycoparasite. A fungus parasitic on other fungi.

mycoparasitism. One fungus living on another. . (16)

mycophagous. Feeding on fungi. (20)

mycoplasma. A wall-less prokaryotic microorganism of the class Mollicutes. (21)

Mycoplasma. A genus of cell wall-less, sterol-requiring, catalase-negative bacteria (family Mycoplasmataceae) occurring as parasites and pathogens. (16)

mycoplasma-like organism. See phytoplasma.

mycorrhiza. A specialized root structure resulting from a symbiotic relationship between a fungus and a higher plant. (Pl. mycorrhizae.) (15)

mycosis. Disease in animals caused by a fungus. (Pl. mycoses.) (20)

mycotoxicosis. Any disease of man or animals resulting from the ingestion of mycotoxins. (16)

mycotoxin. A toxin produced by a fungus. The term is usually reserved for fungal metabolites that are toxic to man and/or animals and are produced by molds growing on foodstuffs (e.g., aflatoxins, ergot alkaloids). (16)

mycotrophic. Refers to green plants having mycorrhizae. (20)

mycovirus. A virus that replicates in cells of fungi. (10)

myxamoeba. A naked cell capable of amoeboid movement; characteristic of the vegetative phase of myxomycetes and such Plasmodiophoromycetes as Plasmodiophora brassicae. (20)

Myxomycetes. See Myxomycota.

Myxomycota. The slime molds, a class of fungi characterized by amoeboid vegetative protoplasts, plasmodia, and by brightly colored spore bearing capillitia. (20)