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idiomorphs. Nucleotide sequences that occupy the same locus in different strains but are not related in sequence or common descent. (19)

imbricate. Overlapping, like the shingles of a roof. (17)

immune. Cannot be infected by a given pathogen. (2)

immunity. 1. The state of being immune. (2) 2. In plants, the ability to remain free from disease because of inherent structural or functional properties. (20)

imperfect fungus. See Deuteromycotina. (7)

imperfect stage. See anamorph.

imperfect state. The state of a fungus characterized by asexual spores (conidia) or the absence of spores. Also called imperfect stage.

incipient. Early in development (of a disease or condition). (5)

incisure. In nematodes: A longitudinal cuticular cleft that divides the lateral fields; sometimes called involution or line. (14)

incompatible. Not cross-fertile. (17)

incubation period. The period of time between penetration of a host by a pathogen and the first appearance of symptoms on the host. (2, 24)

indeterminate. Without definite margin or edge; terminal growth (of hyphae or conidiophores) unrestricted. (17)

indexing. A procedure to determine whether a given plant is infected by a virus. It involves the transfer of a bud, scion, sap etc. from one plant to one or more kinds of indicator plants sensitive to the virus. (2)

indicator host. A plant species that gives characteristic symptoms to a specific virus. Used in virus diagnosis. (10)

infect. Of a parasite: To begin or continue an interactive, usually pathogenic, relationship with the host. (21)

infection. The interaction of parasite with host; the beginning of that interaction. (21)

infection court. A site in or on a host plant where infection can occur. (5)

infection thread. The specialized hypha of a pathogenic fungus that invades tissue of the susceptible plant. (20)

infectious. Capable of producing propagules that disperse from one host to another and infect it. (3)

infective. Of an agent of inoculation, capable of transmitting inoculum. (20)

infest. Of microorganisms and viruses: To contaminate the surface of a plant without establishing an interactive relationship with it; to be present in high numbers in a plant's environment (soil, water, etc.). (3)

ingress. The act, by a plant pathogen, of gaining entrance into the tissues of a susceptible plant. (20)

inoculate. To introduce a microorganism into an environment suitable for its growth; to bring a parasite into contact with a host. (3)

inoculation. The act of inoculating; the placement of microorganisms or viruses at a site where infection is possible (the infection court). (3)

inoculum. The population of microorganisms introduced in an inoculation; the units of a parasite capable of initiating an infection. (3)

inoperculate. Of an ascus or a sporangium, opening by a pore or split to discharge spores, as in asci of the Helotiales. (8)

intercalary. Formed or situated somewhere between apex and base of a given structure. (16)

intercellular. Between cells. (2)

intersex. An individual more or less intermediate in phenotype between male and female, displaying secondary male or female characters. (14)

intracellular. Within or through the cells. (2)

intumescence. Hyperplastic symptom characterized by blister-like swelling on the surfaces of plant organs. (20)

invagination. Retraction, under force of pressure, of an outer surface toward the inside. (20)

in vitro. (Literally "in glass".) Cultivated in an artificial, non-living environment. (3)

in vivo. Within a living organism. (2)

invasion. In plant pathology: Spread of a pathogen through tissues of a diseased plant. (20)

involute. Of the margin of the pileus: Rolled in, especially when young. (17)

involution. See incisure.

isoenzyme. See isozyme.

isogamy. The condition in which gametes are morphologically similar, as in the members of the Zygomycotina. 920)

isogenic. Two or more organisms or cells having identical genotypes. (16)

isolate. In plant pathology: a culture or subpopulation of a microorganism separated from its parent population and maintained in some sort of controlled circumstance; also, to effect such separation and control, for example to isolate a pathogen from diseased plant tissue. (21)

isolation. 1. The process of getting an organism in pure culture. 2. The pure culture itself. (17)

isoline. (Isogenic line.) One line in a series of genetically similar plant lines that carry different specific genes for resistance to a particular pathogen. (11)

isotype. Any duplicate of the holotype of a taxon. (22)

isozyme One of a number of enzymes that catalyse the same reaction(s) but differ from each other in primary structure and/or electrophoretic mobility. (Also isoenzyme.) (16)

isthmus. In nematodes: Relatively narrow portion of esophagus just anterior to the basal region. (14)