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Potato yield, storage and exports
By Hina Kamal
POTATO (Solanum
Tuberesum) is a source of vitamin C, even though the
vitamin content per unit weight is comparatively low.
The amount is highest in new potatoes and falls
gradually during the post harvest storage.
As large amounts of potatoes are consumed, these
contribute more protein and iron than other vegetables
in the average diet and are also useful sources of
thiamine, niacin and several other nutrients including
fibre.
Factors affecting the stability of potato during the
extensive period of pre-harvest growth, storage,
transport, packaging and export can be classified into
three margins, including infection during pre-harvest
growth, physiological and mechanical damages during
post-harvest handling.
Pre-harvest factors are largely responsible for
significant post-harvest losses occurring either during
storage, transport or packaging. These factors include;
seed selection, seed storage, field pests, infection by
disease organisms, pest infestation, environmental and
cultural practices, and genetic factors.
High quality seed should be chosen with low level of
disease or those plants should be used which are
moderately resistant to late blight with thoroughly
clean and disinfect storage facilities and handling
equipment prior to receiving seed potatoes.
During the pre-harvest growth phase, the plant is
exposed to different diseases initiated by infection, if
handling is not appropriate. The infection may start
before harvest, through natural pores in the above and
below ground parts of the plant, which allows the
movement of air, CO2 and water vapour into and out of
the plant and since the pathogenic and spoilage micro
organisms are widely distributed in the air, soil and on
dead and decaying plant material, they result in
inoculating infection.
Severe infections can completely wipe out an otherwise
good crop. In the field, late blight reduces the ability
of the plant to provide nutrients to the tuber, often
resulting in a decrease in the number of marketable
potatoes.
In addition to the loss or yield reduction of a specific
field, neighbouring field can also be at risk due to
mobility of the organism. The quality can be severely
impaired. Late blight tuber rot is a direct result of
the late blight organism and can develop and spread
during the growing season, at harvest and in storage (if
potatoes going into storage are infected). To avoid late
blight disease spores washing onto tubers from infected
vines is conducted. The use of an effective combination
of contact/systemic fungicide needs to be applied in two
phases firstly, when the plants are small i.e., at the
beginning and at the end of season. The magnitude of
loss due to infection is variable.
Another factor is the presence and activity of field
insects which affect the plant in two ways; by boring
holes in tubers thus reducing the quantity and quality
of the produce and germination capacity, and by causing
damage to the epidermis providing entry for moulds and
bacteria to penetrate into the tuber.
Pyralid Moth and Tineidae species are known to create
losses during the pre-harvest stage of plant growth.
Pre-harvest factors are largely responsible for
significant post-harvest losses due to the
interrelationship and interaction between different
components of production and harvesting, of which
respiration is a vital intrinsic force such that: tubers
are living organisms and as such, they respire. The
respiration process results in the oxidation of the
starch (a polymer of glucose) contained within the cells
of the potato tuber which converts it into water, CO2
and heat energy. For respiration to occur freely a
supply of oxygen is needed and the resulting CO2 and
heat have to be removed from the products environment
because a limited supply of oxygen and inadequate
removal of CO2 may lead to effective asphyxiation and
death of product tissue.
Respiration rate of potato varies with the physiological
age of the tuber i.e., whether it is in sprouting or in
dormant phase, whether or not it has been damaged and is
healing its wounds and even by the storage conditions,
mainly temperature. The rate of respiration is
relatively higher at harvest followed shortly by a
decrease, especially during storage, then followed by an
increase once sprouting begins.
Dormancy is considered to be the point of physiological
maturity of potato. During dormancy, the endogenous
metabolic rates are reduced and the tuber depicts no
intrinsic or bud growth, although it retains the
potential for future growth. Hence dry matter losses are
correspondingly reduced. Dormancy is affected by major
extrinsic factors such as temperature, moisture content,
oxygen and CO2 content of the storage atmosphere.
Apart from it, the extent of wounding and any disease of
the tuber may also have an overriding effect. This
provides the fact that while tubers remain dormant they
can be stored satisfactorily. As soon as dormancy is
broken and sprouting begins, the rate of dry matter loss
increases since formation of sprouts require energy
which is drawn from the tubers’ carbohydrate reserves.
This also results in an increase in the rate of water
loss, pathogen penetration. However, it should also be
taken into account that avoidance of sprouting applied
by low temperature leads to sweetening of the tuber,
which is considered to decrease the value of the stored
crop.
The permeability of the skin of the tuber is a function
of its maturity and is significant in the rate of
respiration for example the periderm of freshly
harvested immature tubers is most permeable and thus
permits higher levels of respiration than similarly
harvested mature tubers.
Damage and wound healing increases influence respiration
and the incidence of invasion of pathogens such that the
initial infections cause by the pathogens produces a
breakdown of the host tissues and once these primary
pathogens are established, they are followed by an
invasion by a broad spectrum of secondary pathogens.
Mechanical damages are indeed also vital in keeping the
stability of potato. There are different degrees of
mechanical damages, from small bruises to deep cuts and
they may be sustained at any stage, from pre-harvest
operations, through harvesting and subsequent handling
operations when the product is graded, packed and
transported to market. Serious mechanical injury, which
may result in the product being rejected during grading,
is a direct loss.
Lastly, storage conditions including temperature,
humidity, air movement and water loss are influential in
masking the stability of potato tuber. In this regard
lower storage temperature gradually, maintaining steady
levels of humidity and temperature until all of the
field heat is removed. Continue to maintain steady
levels of temperature and humidity throughout storing
potato, but the rate of air movement needs to be kept as
low as practical to prevent excessive loss of moisture
to avoid the production and spread of moulds, especially
Fusarium Tuber Rot and Silver Scruf. If some decay
occurs, completely open outside air intakes and increase
the ventilation rate until the diseased potatoes dry
out.
Pakistani potatoes are losing export markets which have
created a crisis for growers. The traditional export
markets are Iran, Sri Lanka and Afghanistan. The
streamlines discussed earlier can greatly increase the
yield, storage conditions and export of potato, for
these reasons, the total production market and marketing
system needs to be address as a whole.
Courtesy: The DAWN |
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Pakissan.com;
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