Agriculture Reference
In-Depth Information
16
Potatoes
Chris Bishop, Debbie Rees, Muhammad U. A. Cheema,
Glyn Harper and Graeme Stroud
INTRODUCTION
Potato (
Solanum tuberosum
), sometimes referred to as
“white” or “irish” potato, originated in the highlands of
South America. Today, potato is the fourth most important
food crop in the world after wheat, rice and maize. The
world annual production is approximately 300 million
metric tons. More than one-third of the global potato output
now comes from developing countries and world
production is growing by approximately 4% per anum.
(CIP 2009). The world distribution of potato production is
summarised in Table 16.1.
Primarily, potatoes are grown to be eaten. There is some
production for potato starch but overall this is a small
proportion. Potatoes may be boiled, baked roasted or fried.
Slices fried and eaten hot are known as chips or French
fries, while wafer-thin slices fried and packaged for eating
cold are called crisps, or sometimes chips. The worldwide
market demand for crisps and chips contributes to the
potato's commercial importance. There is a wide range of
varieties grown, and these tend to be devoted to specific
purposes so that commercial processing potato varieties
are not the same as those produced for fresh home
consumption.
generally consists of six to ten suberized cell layers. It is
usually thicker at the stem than at the bud end. Pores, called
lenticels, are visible to the naked eye, and are necessary for
gas exchange as the periderm is almost impermeable to
oxygen and carbon dioxide. Visible potato eyes are the
sites where sprouting occurs. Generally between five and
20 eyes are arranged spirally in each tuber, either evenly
along the length of the tuber, or concentrated at the apical
end (Burton 1989). The main part of the tuber is made up
of starch storing paremchyma cells in the cortex and per-
imedullary zone, which are separated by a ring of vascular
tissue. When a tuber is cut longitudinally, the medullar rays
and medulla which make up the pith can be observed
(Fig. 16.1).
A wide range of characteristics can be observed among
potato varieties, in terms of skin texture and colour, and
flesh colour. (Burton 1989); thus skin may be smooth,
rough, partially netted, totally netted, heavily netted. Skin
colour may be uniform white-cream, yellow, orange,
brownish, pink, red, purplish red, purple, dark purple-
black, or multicoloured and a mixture of two or more of
these. Likewise flesh colour, may be uniform or with sec-
ondary colour- white, cream, yellow, red, violet or purple.
Tubers may be harvested when the above ground parts
of the plant (the haulm) are still green, in which case they
have thin delicate skin and are referred to as “new potatoes”.
Most crops are not harvested until the haulm has died down
either naturally or has been deliberately killed off using
chemicals. In this case the tuber is mature and has
developed a thicker periderm (Snowden 1991).
POST-HARVEST PHYSIOLOGY
The potato plant is a dicotyledon and the tubers develop
from underground shoots or stolons. The structure of the
tuber is illustrated in Figure 16.1 (derived from Diop &
Calverley 1998). The skin, or periderm, can vary in
thickness between varieties and growing conditions, but
