Glossary Plant Breeding

genetic and environmental (non-genetic) causes is called genetic and environmental
variance, respectively. The total variance, that is, genetic plus environmental is
referred to as phenotypic variance. In principle, variance should not be negative.
However, components of genetic variance sometimes turn out to be negative due to
sampling error, poor plot techniques, large experimental error, and the like.
Variant. An individual organism that is recognisably different from an arbitrary standard
type in that species. The basis of the difference may be genetic or non-genetic. It may
also be defined as a putative mutant yet to be tested for heritable nature of the trait
(for which it is a “mutant”).
Variate. A single observation or measurement. In a data set comprising x 1 , x 2 , x 3 , …, x n ,
each observation is a variate, for example. It is a quantity that varies from individual
to individual and aggregate of individual values is called a population.
Variation. The occurrence of differences among individuals due to differences in their
genetic composition and/or environment to which they are exposed. The variation,
which is totally environmental, cannot be exploited in plant breeding. Thus from the
standpoint of practical utility, the variation must be at least partly genetic in origin.
Variational Theory (Darwin 1859). An accepted theory to explain the process of
evolution. In this theory, variation exists among organisms within a species.
Evolution of the species as a whole results from differential rates of reproduction of
the various types, so that the relative frequencies of the types change over time (over
generations). Therefore, evolution in this view, is a sorting process rather than a
transformational one.
Variegation. The occurrence within a tissue of sectors with differing phenotypes.
Variety. A group of individuals within a species, which are distinct in form or function
from other similar arrays of individuals. The term may be used interchangeably for
cultivar. However, the term “cultivar” is commonly used in scientific literature and
must be preferred to variety as the latter is also used in the taxonomy. The distinction
of being named and made commercially available serves to set apart “variety” from
the experimental strain or line. It must have three properties: distinctiveness,
uniformity and stability (DUS). These requirements are clearly satisfied in the
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