Principles of Plant Genetics and Breeding

in two stages. The first stage, called the preliminary
yield trial (PYT), starts at an earlier generation (e.g.,
F 6 , depending on the objectives and method of breeding),
and consists of a larger number of entries (genotypes).
Further, these entries may be planted in fewer
rows per plot (e.g., two rows without borders) and
fewer replications (2–3) than would be used in the final
trial, the advanced yield trial (AYT). Superior genotypes
are identified for more detailed evaluations. The
PYT is designed to be a quick evaluation of the breeding
efforts. The PYT consists of a fewer number of promising
genotypes (10–20), depending on resources. It is
conducted for several years at different locations, using
more replications and plots with more rows and with
border rows. It is also subjected to more detailed statistical
analysis.
Breeders’ trials vary in scope, according to the crop,
its distribution and importance, and resources available
to the breeder. Some breeders (especially in the public
sector) limit their evaluations to within the state or
mandate region. Commercial breeders may conduct
regional, national, and even international trials through
established networks. Public breeders may have wide
networks for trials (e.g., INTSOY – the International
Soybean Program in the USA). In terms of management,
breeders’ trials may also be conducted in one of
two ways – research managed or farmer managed.
1 Research managed. This is a trial conducted at a
research station or experimental farm under the
supervision of researchers. These are usually replicated,
full-scale, and self-contained trials designed
to collect data that can be published in a scientific
publication. Extensive data are often collected.
2 Farmer managed. The trials are conducted on farmers’
fields (see participatory breeding in Chapter 26).
Often, it is a scaled down version of what is conducted
at a research station (fewer replications, fewer
plots, etc.), so that the farmer is not be overburdened.
The breeder may use some creative analysis to
obtain valid data from these trials. For example, different
farmers in the same location may be considered
as a block in a randomized complete block design.
Official trial
After a genotype has been identified as a potential cultivar,
the breeder may seek legal protection by applying
for protection under the Plant Variety Protection (PVP)
Act (see Chapter 15) and/or registration of the cultivar
with an official seed agency. This trial is more detailed than
the performance trial for yield and provides information
PERFORMANCE EVALUATION FOR CROP CULTIVAR RELEASE 419
needed to establish legal identity for the cultivar, showing
its distinctness from existing ones. Data must be
collected to also indicate its uniformity and stability
(i.e., the genotype breeds true from year to year).
Designing field trials
One of the phases of plant breeding in which statistical
analysis is used extensively is the design and conduct of
performance evaluations. The key considerations in the
design of a field trial are as follow:
1 Number of genotypes to evaluate. As previously
indicated, PYTs have more entries than AYTs.
Whereas research-managed trials have the full complement
of genotypes, farmer-managed trials may be
reduced to a small number.
2 Where to conduct the trials (locations). Breeders
usually conduct trials at multiple locations. These
locations, ideally, should be representative of the target
regions for which the cultivars are to be released.
In practice, test locations are seldom randomly
selected. Breeders are limited to sites where they
have collaborators (e.g., institutes, research stations,
universities), or farmers who have an interest in participating
in the project. Where possible, the breeder
should endeavor to test at both research stations
(where an optimal selection environment can be
obtained), as well as at sites that reflect the major
cropping areas and farming practices. Even when
trials are conducted at research-managed sites, efforts
should be made to replicate the actual production
conditions in the farmers’ fields (e.g., crop management
practices). Research institutions often strategically
locate a few research farms in target regions
that represent the climatic and soil conditions of the
area. The total number of sites is variable (about
5–10), but it depends on the extent of variability in
the target region. Areas of major production should
have more sites than those with less production of
the crop.
3 What statistical design to use for field layout.
Randomized complete block designs are commonly
used in breeders’ trials. Research-managed trials may
adopt more sophisticated designs, but farmer-managed
trials should be as simple as possible. The former
should have more replications than the latter, as previously
stated.
4 What data to collect. Researchers at experimental
stations may use equipment and machinery designed
for research (e.g., plot planter and combines). They
have the time and the expertise to collect a wide