Agriculture Reference
In-Depth Information
Figure 4.9
Potato yield assessment trials produce a vast volume of product (tubers) from a relatively small area.
retained and grown in the subsequent year for the first
time under '
ware growing conditions
' in unreplicated
trails at the third clonal year stage. Each selection was
also grown as a six plant plot at the seed site. After the
second clonal year, however, the seed site was only used
to increase clonal tubers and no selection was carried on
the basis of the performance at this site.
At the ware site measurements of a variety of char-
acters were taken and yield was recorded (Figure 4.9).
Thus the third clonal year, was the first one where selec-
tion was based on objective measurements, principally
yield but also other performance characters and disease
reaction. The fourth and fifth clonal generations were
repeats of the third year with reduced numbers of entries
after each successive round of selection but with more
replicates and larger plots, including with larger multi-
plication plots of 20 plants and 100 plants, respectively,
at the seed site.
In the sixth, seventh and eighth clonal generations
surviving clones were evaluated at a number of differ-
ent locations ('
regional trials
') in the United Kingdom.
After each round of trials, the most desirable clones
were advanced (i.e. re-trialled) and less attractive clones
discarded.
Clones that were selected in each of the three year's
regional trials were entered into the UK National
List Trials (a statutory government organized national
testing scheme). Depending on performance in these
trials a decision was made regarding cultivar release
and initial foundation seed lots were initiated. If all
went well, farmers could be growing newly developed
cultivars within 17 years of the initial cross being made.
Time to develop clonal cultivars
Despite the lengthy time period between crossing and
farmers growing a new potato cultivar, this is a short
time period in comparison to some of the other asexually
propagated crops. In potato the long selection process
is related to the difficulty in evaluating a crop where
the phenotype is greatly affected by the environment
(both where the seed and ware crops were grown). In
the case of potato, some of the length of the pro-
cess is related to a slow multiplication rate, around
10 : 1 per generation. In addition, seed tubers are bulky
and require large amounts of storage space. To accom-
modate planting material for one acre of potatoes will
require approximately 2000 lbs of seed tubers.
With many other clonal species the time from cross-
ing to cultivar release can be a very lengthy process.
In apple breeding, for example, it is often said that if
a breeder is successful with the very first parent cross
combination, then it is still unlikely that a cultivar will
be released (from that cross) by the time the breeder
retires! In this case there is the obvious difficulty in the
