Compendium of Potato Diseases - (PDF, 101 mb) - USAID

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Fig 4. Natural openings in a pota~o plant permitting entrance of pathogens: A, stor ate on leaf (bar represents 20 m): B, enlarged lenticels
on tuber surface, usually inconspicuous bit enlarged when soil is wet: C, section through enlarged lenticel (bar represents 100pm); D,
roots emerging through the surface of stems or other roots, producing open wounds (bar represents 100 pm).
S Scrinisha%. and I). t. U. \W'ang, eds. Protein Resources and
I clniology: Status and Rcscarch Needs. Avi Publishing Co., Inc..
Westport, Ct .
VAN I)F R ZAAG. 1). L. 1976. Potato production and uoli/ation in the
world. Potato Res. 19:37-72.
Oxygen-Temperature Relationships
Interrelationships between tuber respiration, gas exchange,
and tuber temperature are operative in the field before, during,
and after tuber enlargement. After harvest, they markedly
influence storage life, seed performance, and market quality,
[he potato tuber is capable of respiring both aerobically and,
for a limited time, anaerobically. Because the natural periderm
Of tihe tub( r is a harrier to gas diffusion, diffusion take:, place
through the lcnticels. I)iffusion rates differ between individual
lenticels. and diffusion is further dependent upon the exposed
intercellular spaces of tile underly:ng tuber tissue. Within the
tuber, gas difLusion takes place through the intercellular spaces,
wkhich occupy close to II( of the internal tuber volume.
Oxygen (():1 is present in the potlato tuber both in the atmosphere
of the intercellular spaces and dissol~ed in the cell sap.
Carbin dioxide WO()) diffuses through lenticels at a rate
approxiniatelv 80( 1 of that for 0). )uring early and rnidseason
stirage. CO: excess and () deficit %%ithinthe tuber are usually
about equal. later in storage (0) evolution mav much exceed
() absorption.
I uber periderin permeability is highest thro iglh immature
skins d uring growth of the crop, decreases du. ir', maturation of
the vines, and reaches a low ic\el after deati of1vines. Permeability
drops considerably during the first five weeks of storage
and gradually rise!, to a level comparable to that of mature
tub,'rs in the field. A thin film of water on the tuber surface
virt dllV stops oxygen diffusion through the lenticels and can
reduce the center of the tuber to anaerobic conditions within 6
hr at 111VC and in 2 hrat 21CC.
Respiration rates of small, medium, and large tubers are
essentially similar per unit of volume tinder satisfactoryenvironmental
condiion... However, the ratio of surface area to total
volume is much higher in small tubers than in large tubers,
Under conditions stimulating high respiration rates (high tem-
WIG(N(IT N, M. .1. 1974. Effects of temperature, oxygen tension and
relative humidity on the wound-healing process in the potato tuber.
Potato Res. 17:200-214.
(Prepared by W. J. Hooker)
perature) or reduced gas diffusion from tuber surfaces (surface
water films), the smaller ratio of surface area to volume in large
tubers may limit gas exchange and cause injury, whereas the
larger ratio in small tubers may enable them to escape damage.
Respiration rates ofimmature tubers are considerably higher
than those of mature tubers early in storage but later become
essentially similar. Respiration of mature tubers immediately
after harvest is often three times that of the same tubers a week
later. This increased respiration is in part associated with
mechanical injury during harvest and storage.
Respiration of potato tubers during storage (Fig. 5) is
or
12
8, _
6
4
C 2
0
0 5 10 15 20 25
Temperature *C
Fig. 5. Respiration rates of potato tubers at various storage
temperatures. (Redrawn from W. G. Burton 1966. By permission
from the author and H. Veenman en Zonen B. V.).
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