Agriculture Reference
In-Depth Information
2
Modes of Reproduction and Types of Cultivar
described by the breeder. The variation should also be
commercially acceptable and occur with no greater a fre-
quency than that defined for that type of cultivar (as we
will see below). The amount of variation that is permit-
ted to exist in released cultivars varies according to the
country of release. For example, in the United States,
provided the degree and type of variation is clearly stated
when the cultivar is released, the breeders can decide
exactly how much heterogeneity exists for any character.
In European countries, regulations regarding unifor-
mity are more clearly defined and requirements for these
to be adhered to. In the United Kingdom the guidelines
read '
The plant variety shall be such that the plants of which
it is composed are, apart from a very few aberrations, and
account being taken of the distinctive features of the repro-
ductive system of the plants, similar or genetically identical
as regards the characteristics, taken as a whole, which are
considered by the Ministers for the purpose of determining
whether the variety is uniform or not
'.
Stability
Stability of a cultivar means that it must
remain true to its description when it is reproduced
or propagated. Again the requirements for this differ
between countries - in Europe it is generally by statute
while in the United States and Canada it is usually con-
sidered to be the responsibility of the breeder to ensure
stability. Again the UK guidelines give a description of
what they mean by stability and it is '
The plant variety
shall continue to exhibit its essential characteristics after
successive reproductions or, where the breeder has defined
a particular cycle of reproduction, at the end of each cycle
of reproduction
'.
INTRODUCTION
The most appropriate type of cultivar which can be
developed to best fit the needs of a production situation
will be determined, in part, by the breeding system and
mode of reproduction of the species involved.
A cultivar (or variety) is defined as a group of one or
more genotypes which have a combination of characters
giving it
distinctness, uniformity
and
stability
(DUS).
Distinctness
When a cultivar is 'released' for produc-
tion it has to be proven that it is indeed new and that
it is distinct from other already available cultivars. Dis-
tinctness is often defined on the basis of morphological
characters that are known not to be greatly influenced by
the environment. But other features such as physiology,
disease or virus reaction, insect resistance and chemical
quality may be used as well as, increasingly, molecular
characterization in some countries (i.e. DNA markers).
In the Guide to UK National Listings distinctness is
described as follows: '
The variety, whatever the origin,
artificial or natural, of the initial variation from which it
has resulted shall be clearly distinguishable, by one or more
important characteristics, from any other plant variety
'.
This requirement is in part to ensure that new cultivars
have not previously been registered by other breeding
organizations. Information used to determine distinct-
ness, also can be used later to identify and protect
proprietary ownership of that cultivar so that other orga-
nizations cannot register the same cultivar or trade with-
out permission, (within a set period) in that cultivar.
Uniformity
Uniformity is related to the level and
type of variation which is exhibited (usually phenotypic)
between different plants within the cultivar. Any such
variation should be predictable and capable of being
The requirement of distinctness is needed to protect
proprietary cultivars and ensure that different orga-
nizations are not trying to claim the same cultivar
and identify such cultivars as to their breeder. The
