Agriculture Reference
In-Depth Information
good links are set up with industry personnel and that
the breeding programme tries to integrate ideas from
the processing industry into the breeding strategy as
much as is feasible. This will also allow experiments
to establish the levels of relationship (the correlations)
between the 'lab tests' and the behaviour of the lines in
commercial practice.
In other instances it is easier to record a related char-
acter than to record the trait itself. For example, in
rapeseed breeding it is desirable to have low glucosi-
nolate content in seed meal. Glucosinolate breakdown
products are highly toxic and can cause dietary prob-
lems when seed meal is fed to livestock. Determining
glucosinolate content is a two-day process and expen-
sive. A much quicker and less expensive alternative
is available. One of the breakdown products of glu-
cosinolates is glucose. It is possible to obtain a good
estimate of glucosinolate content simply by crushing a
few seeds, adding water and estimating glucose concen-
tration, using glucose sensitive paper. Similarly, malt
barley breeders evaluate and select breeding lines for
seed nitrogen content and soluble carbohydrates, which
are highly related to the malting quality traits of malt
extract and oligosaccharides, but these latter two char-
acteristics are difficult to assess with small quantities
of seed. Finally, the quality objectives of forage/fodder
breeding programmes are biological in character and
would ideally be met by testing the growth of animals
fed on the breeding lines, but these large-scale feed stud-
ies are virtually never carried out, for reasons of time
and cost. It should always be remembered, however,
that these quality determinations are, at best, predic-
tions, and in many cases, only a crude estimate of the
character which is actually to be selected for.
Plant breeders seek to predict quality, however com-
plex, by relatively simple measurements or organoleptic
tests. Often small scale testing units based on the larger
operation are used but in many cases quality assessment
is determined by the correlation or relationship between
an easily measured character and the more difficult to
assess trait. However, before a new cultivar is released
into agriculture it is desirable that new genotypes be
tested on a commercial scale process. So wheats should
be milled in a commercial mill, barleys should be malted
and beer made, potatoes should be French fried and
sold in fast food stores, onions stored in commercial
storage and fodder fed to livestock before the product
is released.
It is only after several rounds of testing at the com-
mercial level that a secondary factor can be accurately
estimated - that is the uniformity of quality. Uniformity
of quality is as important as the actual quality charac-
ter itself. A cultivar, which produces excellent quality
in one environment or year but unacceptable quality in
others, will have little merit in commercial production.
Unfortunately, uniformity in quality (although one of
the most important characters of a new cultivar) is dif-
ficult to assess within the restrictions of a feasible sized
breeding scheme.
Overall, quality is what creates the demand for a
product. It is the end-user who will mostly determine if
that crop will be grown in future years. It is a very naive
breeder who ignores the fact that consumer preference
is continually changing and that the quality standards of
today may be superseded by a new set of standards in the
future. It is therefore imperative to organize a breeding
scheme to be flexible and to try to cover as many poten-
tial aspects of yield, quality and other factors which may
be important in the next two decades.
INCREASING PEST AND DISEASE
RESISTANCE
A major limiting factor affecting both harvested yield
and end-use quality of agricultural and horticultural
crops is infection or infestation by plant pests and dis-
eases. Breeding cultivars that are genetically resistant to
pests and diseases is still a primary objective of plant
breeding.
The development of resistant cultivars involves con-
sideration of the genetic variability of the pest or disease
as well as the variability in resistance (or tolerance) that
exists within the crop species (or related species from
which resistance can often be obtained). The durability
of resistance of developed cultivars can be affected by
the emergence of new races of the disease/pest that are
able to overcome the resistance mechanism in the host
plants. Thus the longevity of disease resistance that can
be achieved in a new cultivar is often as important as
the extent or degree of resistance that the new cultivar
actually exhibits.
The major forms of disease and pests include fungi
(air- and soil-borne), bacteria, viruses, eelworms and
insects. However, this is not an exhaustive list. Other
damage can occur (e.g.
bird damage and mammal
