Agriculture Reference
In-Depth Information
the previous single-hill generation, as does posi-
tive selection for tuber type. The larger number of
tubers in the 12H plots also allows for tubers to be
cut in the field to allow evaluations for internal
defects such as brown center/hollow heart, and
vascular and stem-end discolorations; with plots
being left in the field, where a high percentage of
internal defects are noted. In the single hill, with
almost all tubers needed for seed for 12H plots, se-
lection against internal defects is not readily ap-
plicable during the selection process.
Annually,
20-
25% of 12H plots are se-
lected in the field, with all tubers of a plot being
harvested. Yield obtained from the plots is ad-
equate for the first time to allow the collection of
data on specific gravity (dry matter content), as
well as processing attributes (fry or chip color)
following approximately 5 months storage at 4.4
and 7.2°C. Following the obtainment of process-
ing data, tubers of all field-selected 12H plots are
inspected visually in the cellar for final dispos-
ition, with processing data and storage charac-
teristics such as tuber dormancy and shrinkage,
stem-end/vascular discoloration, skin color re-
tention (in the case of red- or purple-skinned se-
lections), and storage rots (dry and soft) all being
factored into the final determination of which
breeding clones advance or are discarded in the
breeding program. This final cellar disposition in
March results in the discard of an additional
50-
60% of the 12H breeding clones originally
selected in the field the previous fall.
merit of breeding clones without the confound-
ing presence of viruses.
Replicated trials in the third field season in
the Aberdeen program are the first opportunity
for statistical inferences to be made among
breeding clones relative to check cultivars, espe-
cially in the context of yield, which up to this
point has not been a primary determinant in the
advancement of a breeding clone due to the first
and second field generations being non-replicated.
Most potato breeding programs use a random-
ized complete-block design. Data are collected
on total yield, as well as on marketable yield (US
No 1); US No
1
yield comprising all tubers
greater than 4.8 cm diameter (approximately
113.4 g) and with cull tubers, with defects such
as second growth and growth cracks having
been removed, as well as any tubers showing wet
rot. In addition, tubers of a breeding clone with
the potential for processing or fresh market rus-
set usage are separated by size into weight
categories of less than 113.4, 113.4-170.0,
170.1-283.5, and >283.5 g. Tuber size distri-
bution is important to the fresh pack and pro-
cessing industries, with market usage defining
desirable tuber size. For example, the 170.1-
283.5 g (6.4-8.3 cm diameter) is of importance
for processing into French fries and other frozen
potato products, whereas smaller size tubers
with diameters of 1.9-6.4 cm (≤170.1 g) are de-
sired for fresh pack of specialty cultivars having
unique skin or flesh colors, where smaller size
commands a premium price from consumers.
Tubers ranging in size from 226.8 to 396.9 g are
the most valuable for the russet fresh pack in-
dustry (Guenthner, 2003), with those sizes
being used in “count cartons” of varying tuber
numbers based on tuber size (e.g. a
60-
count
carton would contain
60
tubers ranging in
weight from 283.5 to 453.6 g).
Besides yield data, other characteristics of
breeding clones evaluated for the first time in the
third field season include blackspot bruise sus-
ceptibility and storage disease response follow-
ing inoculation with
Erwinia
and
Fusarium
for
soft and dry rot, respectively. The ability to store
for prolonged durations in storage is important
to the industry of the western USA, with tubers
of the long dormancy cultivar, Russet Burbank,
being stored for periods as long as
9-
10 months
following harvest; increased susceptibility to
storage rots relative to industry standards is
Seed increase and replicated trials
(3rd field generation and higher)
Ten tubers of 12H breeding clones retained for
advancement in the breeding program are as-
sayed for the presence of the three major potato
viruses, PVY, PVX, and PLRV, using ELISA.
Those tubers free from all viruses are planted in
a seed increase plot at a field site isolated from
any nearby commercial production to decrease
the possibility of current-season infection by vir-
uliferous aphids. The number of individuals rep-
resented in previous field generations does not
allow for the cost-effective evaluation for virus
until numbers are made more manageable at the
end of the 2nd field season. Virus-free seed is
crucial to the success of a potato breeding program
in allowing for accurate assessments of the
