Glossary Plant Breeding

species, S. spontaneum. One of the seedling of this interspecific cross provided Co
205 that became commercially acceptable in sub-tropical India, and later replaced the
then existing varieties belonging to the species S. barberi.
Coefficient of Variation. A measure of relative dispersion for the purpose of comparing
two or more statistical series. The series may differ in respect of standard deviation,
means or both or may differ in units. However, cv, which is a percentage, and
therefore, unitless can be used to compare variability present in them. Numerically, it
is standard deviation expressed as the percentage of mean [cv = (σ/μ) x 100]. It
remains unaltered by a change in scale; but it is altered by a change of origin, which
affects the mean but not the standard deviation. The cv, as used in breeding
experiments, expresses experimental error as the percentage of mean. Numerically, cv
=[(σ 2 e) ½ / μ] x 100. It indicates the degree of precision with which the treatments
are compared, and is a good index of the reliability of the experiment. Thus higher the
cv value, the lower is the reliability of the experiment. The cv varies greatly with the
type of experiment, the crop being grown, the crop season, and the character
measured.
Cohorts. Progenies from different crosses in the same generation included for
simultaneous evaluation in the test nursery.
Combining Ability. The ability to produce superior hybrids when crossed with other
appropriate inbreds.
Commensalism. A kind of interaction in biotic community in which one population
(commensal) benefits but the second (host) is unaffected.
Common Phenolics. Phenolic compounds found in plants. These are present in small
concentration in both resistant and susceptible plants; but their synthesis or
accumulations appear to be accelerated following infection. These are toxic to the
pathogens, and their production and accumulations proceed at a faster rate after
infection in a resistant variety than in the susceptible one.
Community. In ecological sense, all the populations occupying a given area.
Competition Effect. Interdependence of adjacent plants because of their common need
for limited available resources such as sunshine, soil nutrients, moisture, CO 2 , O 2 , and
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