Agriculture Reference
In-Depth Information
suitable off-season location for growth and
inspection. This is common in the USA and
Canada, where the samples are planted during
the winter months in temperate southern cli-
mates like Florida, Arizona, California, and Ha-
waii, or in a greenhouse.
After plant foliage reaches a
40-
50 cm
height, inspections are conducted by official
certification personnel, who look for disease
problems, varietal mixtures that may have gone
unnoticed during the growing season, or viruses
that were spread too late in the season to detect.
Inspections are one of the main methods for de-
termining if undetectable levels of disease have
moved into the lot, if cultivar mixing took place
during harvest or storage, or if any chemical
carry-over has occurred. In some cases, these
evaluations are the final tool to determine if a lot
should be eligible for sale as certified seed.
In most other cases, postharvest testing is
used to determine re-certification eligibility for
the following year. If field growth is not possible
or preferred, agencies will use greenhouses to
grow the tubers and either visually read or use
laboratory testing techniques to examine the
tubers for the presence of various pathogens—
especially virus-related problems (NIVAP, 2005).
Finally, agencies routinely test individual tubers
for the presence of specific issues (primarily vir-
uses) in lieu of field or greenhouse growth.
Testing can be very effective and is useful in
separating out lots exceeding tolerance levels for
certified seed. The disadvantages are that testing
must be pathogen specific (thus chemical
carry-over may be difficult, if not impossible, to
detect), and often costs are higher. However, test-
ing can be performed at almost any time after
the sample has been taken and stand issues, in-
sect problems, and other normal situations of
field growth are not a problem.
Once again, disease tolerances are employed
to verify seed lot status. The earlier the generation or
class of seed, the lower the tolerances allowed. In the
USA, the State/National Harmonization Program
allows for no more than 1% of the samples to be
infected with mosaic-type viruses, and no more than
0.5% infected with
Potato leaf roll virus
(USDA, 2006).
In the Netherlands, however, each class of seed falls
within a certain range of virus allowed with class S
(the basic seed), having a tolerance of 0 plants out of
200,
while class C (the oldest generation) is allowed a
tolerance of
10
plants out of
100
(NIVAP, 2005).
Storage inspections
In countries with certification systems, storage
inspections are conducted on each facility hold-
ing seed potatoes. Inspectors check the adequacy
of the storage units to be sure they are capable of
holding seed at the appropriate temperatures
(
3-
4°C), relative humidity (95% +), and that air
flow into the bins is adequate to prevent un-
wanted sprouting. Often, seed lots are harvested
and stored in cribs (typically holding around
0.5 to
1
t per unit), which may be stacked to fill the
storage area or are stored in bins as a bulk unit.
Bins for bulk storage are normally in the
450-1200 t range, to maintain adequate isola-
tion and manage the environment appropriately.
Inspectors also check the location of each
lot within the structure, verify the number of
metric tonnes stored, and verify each seed lot is
adequately identified by a label or tag. Seed lots
within the storage unit are also examined for the
presence of tuber issues (rots, cultivar mixing,
etc.), and maps of the storage unit with seed lot
locations are produced. These steps allow each
seed lot to have complete traceability from the
application process, to the field growth, and finally
to the storage unit. Once in storage, no sprout in-
hibitors are allowed on the seed to prevent later
problems with germination.
Tagging and shipping point inspection
When seed lots are sold, they are prepared for de-
livery to the buyer. No seed potatoes can be
moved into the marketplace unless they have
had an official shipping point inspection and are
tagged as certified seed. Shipping point inspec-
tions are conducted to confirm each seed lot
meets the grade standards for diseases and size,
has contaminants (such as adhering soil) within
tolerances, and has appropriate physiological
condition (no excessive sprouting, bruising, or
other issues indicative of tuber problems). It is
during these inspections that samples are taken
from the lot as it is being loaded into the shipping
conveyance. After examining each sample, the
inspector can make a determination about the
seeds' status.
Common tuber diseases examined during
inspection include wet rot, dry rot, and late
