IAA Indoleacetic acid, a natural hormone. See also auxin.

illegitimate recombination Recombination between DNA species that show little or no homology. Illegitimate recombination is promoted by transposable elements. See also transposition.

illuminanceSee light intensity.

immune Not subject to attack by a specified pest. Immunity is absolute.

IMP Inosine 5'-monophosphate.

in vitro Part II.

in vitro dry matter disappearance A gravimetric measurement of the amount of dry matter lost upon filtration following the incubation of forage in test tubes with rumen microflora, usually expressed as a percentage: (Wt. dry matter sample - wt. residue) / (weight dry matter sample). Abbr.: IVDMD. Synonym: in vitro digestible dry matter (IVDDM). Usage: The term disappearance is preferred to digestibility. Compare: in vitro organic matter disappearance.

in vitro propagation Propagation of plants in a controlled, artificial environment using plastic or glass vessels, aseptic techniques, and a defined growth medium. See also micropropagation.

in vitro translation The synthesis of proteins in the test tube using purified mRNA molecules and cell extracts containing ribosomal subunits, the necessary protein factors, tRNA molecules, and aminoacyl tRNA synthetases. ATP, GTP, amino acids, and an enzyme system for regenerating the nucleoside triphosphates are added to the mix. Prokaryotic translation systems are usually prepared from Escherichia coli or Bacillus stearothermophilus. Eukaryotic systems usually employ rabbit reticulocyte lysates or wheatgerm extracts. Synonym: cell-free translation.

in vivo nylon bag technique System of determining dry matter disappearance of forage placed in fine-mesh nylon bags, either placed in the rumen or suspended in the rumen from a canula cover of a fistulated animal.

incidenceUsage: Refers to the presence of a measured characteristic. In tall fescue studies, the term may (if properly defined earlier in a publication) be used to refer to, e.g., the number of infected plants or, if expressed as a percentage or in hundredths, to the rate of occurrence of a specified fungus in or on a known number of plants.

incomplete digestSee partial digest.

indehiscent Not splitting open at maturity. Compare dehiscence.

indeterminate inflorescence Flowers arising laterally and successively as the floral axis elongates.

indigenous A plant native to the location where it is growing.

inducible The capability of a gene (or its promoter) to increase transcription when exposed to an inducing agent. Compare constitutive.

infectionUsage: Infection may be used as a general term to denote the presence of a symbiont (such as the endophytic fungus Acremonium coenophialum in tall fescue); no pathogenic relationship is implied. Endophyte presence is the preferred term, but infection is definitely preferred over infestation, which is not appropriate for an endophyte.

initiation (1) Inception of a new organ, as in organ formation at a meristem (e.g., leaf and floral part initiation at the shoot apical meristem), activation of an existing meristem (cambia in shoots and potential underground storage organs), or development of a new meristem (lateral root initiation, adventitious bud initiation). (2) A morphological change of the growing point from the vegetative condition to the floral condition.

initiation codonSee start codon.

initiator codonSee start codon.

inoculation The physical process of applying inoculant to seed or soil.

insert The piece of foreign DNA introduced into a vector molecule.

insertion sequence A class of small (several hundred base pairs) bacterial DNA elements capable of transposition and thus inactivating a gene into which it inserts. Its presence is generally detected by loss of the target gene's function. Abbr.: IS.

integration The recombinational insertion of a small DNA molecule such as a virus into a larger one such as its host. Circular molecules require one crossover for insertion; linear molecules require two.

intensity of cultureSee cultural intensity.

intermittent grazing A method that imposes grazing for indefinite periods at irregular intervals.

interseeding Seeding between sod plugs, sod strips, rows, or sprigs, or seeding into turf to improve the stand or alter its composition.

intervening sequenceSee intron.

introduced species A species not part of the original fauna or flora of the area in question; i.e., brought by human activity from another geographical region.

inverted repeat Two or more regions of DNA that have identical (or nearly identical) nucleotide sequences in the opposite orientation within a single DNA molecule. Inverted repeats may be either contiguous or separated on the same molecule. Compare direct repeat.

irrigation, automatic Hydraulic-electric control of irrigation in response to a transducer that senses plant needs. The term is commonly used more loosely to refer to hydraulic or electrically actuated valves manually present on a time-based controller.

irrigation, semiautomatic An irrigation system in which valves respond directly to a manually operated remote-control switch.

ISSee insertion sequence.

isochromosome Chromosome with arms equal in length and genetically identical, but with the loci in reverse order; produced when the centromere splits transversely.

isogenic Differing in genotype by only one or a very few genes.

isozymeSee isoenzyme.