Principles of Plant Genetics and Breeding

Advantages
1 It is the simplest of the designs to use and analyze.
2 It yields the highest number of degrees of freedom
for error, making the level of error to be of the relatively
lowest magnitude compared to other designs.
3 Missing data, when they occur, do not complicate the
analysis.
Disadvantages It is not conducive for field studies for
obvious reasons of soil heterogeneity.
A typical ANOVA table for a CRD for 15 entries and
four replications is as follows:
Source df
Treatment 14
Error 45
Total 59
Complete block designs: randomized complete block
design (RCBD)
In this design, there are as many blocks as there are
replicates. Each replicate of a genotype is represented
in each block. This design is suitable for a test involving
a small number of entries. It is the most widely used
experimental design in plant breeding.
Advantages
1 It is flexible, being applicable to small as well as moderately
large entries.
2 It is relatively easy to conduct. The field layout and
statistical analysis are relatively straightforward.
3 Unbiased error can be effectively estimated.
Disadvantages
1 It is applicable to evaluations in a homogeneous
environment.
2 It is not suitable for a large number of entries.
A typical ANOVA for an RCBD for 15 entries and four
replications is as follows:
Source df
Blocks 3
Treatment 14
Error 42
Total 59
Complete block designs: Latin square
In Latin square design, blocking is used to control
environmental variation in two directions. It is best used
PERFORMANCE EVALUATION FOR CROP CULTIVAR RELEASE 431
when field variation occurs in two directions, perpendicular
to each other.
Incomplete block designs: lattice design
The lattice design is a preferred design for evaluating a
large number of genotypes.
Advantages
1 It allows unbiased error to be estimated to determine
the origin (genetic or environmental) of observed
variation among genotypes.
2 It provides more effective comparison among genotypes.
Disadvantages Randomization and statistical analysis
for design can be challenging (without the use of a
computer).
Materials, equipment, and machinery for
field evaluation of genotypes
Plant breeding, even on a small scale, entails the evaluation
of large numbers of genotypes. Modern technology
has enabled certain aspects of the field testing process to
be mechanized. Some of the materials, equipment, and
machinery commonly used in plant breeding field tests
are discussed here.
Materials
1 Field plan. A notebook or field record book is prepared
to show the layout of plots according to the
experimental design. The layout also shows the treatment
assignments to plots.
2 Labels/stakes. Computer software such as MSTAT
will allow the plant breeder to select a design, allocate
treatment to plots, print labels for seed envelopes,
print a field layout, and print record books for the
study, among other options. Stakes (wooden, plastic)
are prepared to identify the plots.
3 Seed envelopes. The computer labels are pasted on
paper envelopes. Some breeding programs use cloth
bags, in which case labels are pasted on card labels
and fastened to the sack by means of wires. Breeders
may use permanent ink pens to prepare their labels.
4 Seed treatment. Treatment of the seed with fungicides
may be needed. A bucket (or an appropriate
container) may be needed for the process.
5 Record books. Data collection is facilitated by having
record books printed according to the field plan
and traits to be scored.