variable stocking The practice of allowing a variable number of animals on a fixed area of land during the time when grazing is allowed. Compare set stocking.

variant Seeds or plants that (i) are distinct within the variety but occur naturally in the variety, (ii) are stable and predictable with a degree of reliability comparable to other varieties of the same kind, within recognized tolerances, when the variety is reproduced or reconstituted, and (iii) were originally a part of the variety as released. Usage: Variants are not the same as off-types.

variety A distinct, uniform, and stable assemblage of cultivated individuals that make up a subdivision of their kind: distinct in that the variety can be differentiated by one or more identifiable morphological, physiological, cytological, chemical, or other characteristics from all other varieties of public knowledge; uniform in that variations in essential and distinctive characteristics are describable; and stable in the sense that the variety is true-breeding (i.e., will remain unchanged, to a reasonable degree of reliability, in its essential and distinctive characteristics and its uniformity, when reproduced or reconstituted as required by the different categories of varieties). Usage: Especially when a variety has been registered, the term cultivar is preferred, to avoid confusion with botanical variety. See also race; strain.

vascular tissue Conducting tissue with vessels or ducts.

vector The plasmid or phage chromosome used to carry cloned DNA in recombinant DNA experiments. A vector generally contains one or more unique restriction sites, is capable of autonomous replication in a defined host, and confers a well-defined, selectable phenotype on the host organism (e.g., drug resistance). Compare vehicle. See also expression vector; replacement vector; shuttle vector.

vegetative cover A soil cover of plants irrespective of species.

vegetative propagation Asexual propagation using pieces of vegetation (e.g., sprigs or sod pieces). Compare vegetative reproduction. See also Part II.

vegetative stage The developmental stage prior to the appearance of fruiting structures. See also pasture stage; whorl stage.

vehicle The host organism used for the replication or expression of a cloned gene or other sequence in a plasmid or phage vector.

vernalization Floral induction by low temperatures.

verticuttingSee vertical mower.

vigor Indicative of active growth, relative absence of disease or other stresses. See also plant vigor index.

vitreous Characterizing slightly translucent kernels; usually, but not always, associated with hardness. Synonym (in maize): flinty. Compare chalky.

volunteer plants Plants that occur (in a population) not as a result of current seeding (of the crop under consideration) but resulting from seeds or propagative vegetative parts growing uncontrolled from previous seeding or from plants escaped from cultivation that have been scattered by natural means.