Agriculture Reference
In-Depth Information
9
Some Practical Considerations
tolerance or resistance) or increased profit (e.g. reducing
input costs by incorporation of disease resistance).
In each of the cases it will always be necessary to
evaluate the performance of breeding lines for qualita-
tive and quantitative characters. In some instances it is
possible to select and screen for single gene characters
without the complication of interaction with environ-
mental factors. However, it is accepted that virtually all
quantitatively inherited characters (most often the ones
with greatest commercial value, e.g. yield, quality and
many durable disease resistances) are highly modifiable
by the environment. Consider the observation of a sin-
gle plant; the aim is to minimize the non-genetic effect
from the equation:
P
INTRODUCTION
As noted at the beginning of this topic, plant breeding
demands a range of skills including good manage-
ment and a multitude of other scientific disciplines in
combination, to achieve success. Plant breeding oper-
ations and evaluation of plant breeding lines will be
conducted in laboratories, glasshouses and field sit-
uations. This final section attempts to outline some
of the practical difficulties in a plant breeding pro-
gramme. Sections covered in this chapter examine:
experimental design, including the types of designs suit-
able for different parts of a plant breeding programme;
glasshouse management and field management and the
applications that can be covered and managed using
computers. Finally, this chapter considers some of the
practical considerations of the actual cultivar release
procedure.
2
e
where P is the phenotypic expression, G is the geno-
typic effect, E is the effect of environmental variables,
G
=
+
+
(
×
)
+
σ
G
E
G
E
×
E is the effects attributable to the interaction of
the genotype with the environment effects and
e
is
a random error term associated with a single observa-
tion. In the evaluation of breeding material it is only
possible to observe the phenotype (a combination of
genotypic and environmental effects). The aim is to
determine the genetic potential of each breeding line,
and hence it is necessary to either estimate or mini-
mize the environmental and error effects. To achieve
this demands careful use of a number of
experimental
designs
.
Running a plant breeding programme is no different
from organizing a whole series of scientific experiments
and therefore all aspects of the operation should be
treated with the same care and detail that individual
experiments should be planned and handled. Good
experimental design leads to knowledge of the accu-
racy of the data on which evaluation and selection are
based. The quality of information collected in a plant
σ
EXPERIMENTAL DESIGN
It has been stressed previously that the basic operations
of cultivar development can, for simplicity, be divided
into three stages: producing genetic variation, selec-
tion among recombinants for desirable new cultivars
with specific characteristics, followed by stabilization
and multiplication. The following few sections are con-
cerned particularly with the middle one of the three
processes.
The aim in selection is to identify recombinants,
which are genetically superior to existing cultivars.
Superiority can be achieved by increased productiv-
ity (e.g. increased yield or better end-use quality), by
making productivity less variable (e.g. reduced risk of
crop failure by introduction of disease, insect or stress
