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

IAA
94 /
I Am
/N
F. n iFig. 26. Photochemical oxidant injury, first evident as collapse of
Fig. 25. Lightning damage, showing irregularly affected area. palisade mesophyll. Bar represents 50 pm.
Air Pollution: Photochemical Oxidants progresses upwards. Later, plants become generally chlorotic,
with premature leaf death progressing usually from the bottom
upward.
Potato
Leaves eventually
injury by photochemical
drop but do not
oxidants
abscise rapidly.
such as ozone, Lower leaf surfaces may be light in color occasionally with a
probably peroxyacetyl nitrate, and related compounds has glazed or silvery sheen.
recently been recognized. Symptom differences in the field Except for severe reduction in yield associated
between
with
the
veryearly
several photochemical oxidants have not yet been senescence, tuber symptoms have not been reported.
determined. Losses in sensitive cultivars may be severe Symptoms become evident within 24 hr following
following
heavy
exposure early in the season, exposure, but symptoms of advanced necrosis and chlorsis may
require 10-14 days.
Symptoms
Histopathology
Upper leaf surfaces are stippled by darkly pigmented spots, Palisade mesophyll cells are first affected (Fig. 26), becoming
sometimes with chlorosis and often with a bronzed appearance water-soaked and later necrotic. The spongy mesophyll and
(Plate 6). Injury is most severe on the lower, older leaves and epidermis collapse later.
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