ABIOTIC DISEASES

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ABIOTIC DISEASES

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Abiotic Diseases

• Physiological (nutritional deficiency)
• Macroelements (N, P, K, Mg, Ca)

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Nitrogen (N)
Nitrogen (N) a major element needed by all
green plants. It is transported from older growth
to new growth.
Under nitrogen deficiency, chlorotic (yellow
color) symptoms and light red cast can be seen on
the veins and petioles of leaves the older
mature leaves gradually change from their normal
characteristic green appearance to a much paler
green. As the deficiency progresses these older
leaves become uniformly yellow over the entire
leaf including the veins. Leaves approach a
yellowish white color under extreme deficiency.
The young leaves at the top of the plant maintain
a green but paler color and tend to become
smaller in size. Branching is reduced in
nitrogen deficient plants resulting in short,
spindly plants (long week stem with poor root
development).
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Phosphorus (P)
Phosphorus (P) an important mineral that stores
energy in plants, also a flowering agent.
The P-deficient leaves show some necrotic spots.
A major visual symptom is that the plants are
dwarfed or stunted Phosphorus deficient plants
develop very slowly in relation to other plants
growing under similar environmental conditions
but without phosphorus deficiency. Some species
such as tomato, lettuce, corn and the brassicas
develop a distinct purpling of the stem, petiole
and the under sides of the leaves. Under severe
deficiency conditions, there is also a tendency
for leaves to develop a blue-gray luster. In
older leaves under very severe deficiency
conditions a brown netted veining of the leaves
may develop.
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Potassium (K)
Potassium (K) a nitrogen catalyst needed for
enzyme manufacture.
K-deficient leaves show marginal and tip necrosis
(burn and dead), others at a more advanced
deficiency status show necrosis in the
interveinal spaces between the main veins along
with interveinal chlorosis. Under sever
conditions, wilting and drying of the plant due
to poor water uptake.
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Magnesium (Mg)
Magnesium (Mg) is important in photosynthesis
and the chlorophyll molecule where light energy
is converted to chemical energy. Chlorophyll
gives plants their green color.
The Mg-deficient leaves show advanced interveinal chlorosis, with necrosis developing in the highly chlorotic tissue. In its advanced form, magnesium deficiency may superficially resemble potassium deficiency. In the case of magnesium deficiency the symptoms generally start with mottled chlorotic areas developing in the interveinal tissue. The interveinal laminae tissue tends to expand proportionately more than the other leaf tissues, producing a raised puckered surface, with the top of the puckers progressively going from chlorotic to necrotic tissue. Later, leaf tips curl, entire plant turns yellow and dies. Magnesium is mobile and is transported from older to newer growth. Old growth is affected first. In some plants such as the Brassica, tints of orange, yellow, and purple may also develop.                                            
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Calcium (Ca)
Calcium (Ca) helps form the structural parts of
the plants (it is a major element in cell walls).
The very low mobility of Ca is a major factor
determining the expression of
Ca-deficiency symptoms in plants. The
Ca-deficient leaves show necrosis around the base
of the leaves (soft dead necrotic tissue at
rapidly growing areas), which is generally
related to poor translocation of calcium to the
tissue rather than a low external supply of
calcium. Very slow growing plants with a
deficient supply of calcium may re-translocate
sufficient calcium from older leaves to maintain
growth with only a marginal chlorosis of the
leaves. This ultimately results in the margins of
the leaves growing more slowly than the rest of
the leaf, causing the leaf to cup downward. This
symptom often progresses to the point where the
petioles develop but the leaves do not, leaving
only a dark bit of necrotic tissue at the top of
each petiole.
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Abiotic Diseases (cont.)

• Physiological (nutritional deficiency) (cont.)
• (ii) Microelements (Cu, Fe, Zn, S, B, Mo)

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(Cu) Copper
Copper (Cu) is needed in only small amounts. This
metal aids in plant metabolism and general
health. It helps ward off disease and pests, aids
in the utilization of iron and the manufacture of
enzymes.
These Cu-deficient leaves are curled, and their
petioles bend downward. Copper deficiency may be
expressed as a light overall chlorosis along with
the permanent loss of turgor in the young leaves.
Recently matured leaves show netted, green
veining with areas bleaching to a whitish gray.
Some leaves develop sunken necrotic spots and
have a tendency to bend downward. Trees under
chronic copper deficiency develop a rosette form
of growth. Leaves are small and chlorotic with
spotty necrosis.
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Iron (Fe)
Iron (Fe) is an important constituent of
enzymes and plays a role in photosynthesis.
The Fe-deficient leaves show strong chlorosis
(yellow) at the base of the leaves with some
green netting. The most common symptom for
Fe-deficiency starts out as an interveinal
chlorosis of the youngest leaves (low mobility of
Fe), evolves into an overall chlorosis, and ends
as a totally bleached leaf (white). The bleached
areas often develop necrotic spots. Up until the
time the leaves become almost completely white
they will recover upon application of iron. In
the recovery phase the veins are the first to
recover as indicated by their bright green color.
This distinct venial re-greening observed during
iron recovery is probably the most recognizable
symptom in all of classical plant nutrition.
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Zinc (Zn)
Zinc (Zn) is needed in small amounts for growth
and chlorophyll synthesis.
The Zn-deficient leaves show an advanced case of
interveinal necrosis. In the early stages of zinc
deficiency the younger leaves become yellow and
pitting develops in the interveinal upper
surfaces of the mature leaves. As the deficiency
progress, these symptoms develop into an intense
interveinal necrosis but the main veins remain
green, as in the symptoms of recovering iron
deficiency. In many plants, especially trees,
the leaves become very small and the internodes
shorten, producing a rosette like appearance
(short stem internodes).
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Sulfur (S)
Sulfur (S) is a building block of amino acids
and proteins. Used in small amounts, it aids
transpiration and transport of other elements.
The S-deficient leaves show a general overall
chlorosis while still retaining some green color.
The veins and petioles show a very distinct
reddish color. The visual symptoms of sulfur
deficiency are very similar to the chlorosis
found in nitrogen deficiency. However, in sulfur
deficiency the yellowing is much more uniform
over the entire plant including young leaves. The
reddish color often found on the underside of the
leaves and the petioles has a more pinkish tone
and is much less vivid than that found in
nitrogen deficiency. With advanced sulfur
deficiency brown lesions and/or necrotic spots
often develop along the petiole, and the leaves
tend to become more erect and often twisted and
brittle.
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Boron (B)
Boron (B) is needed in small amounts. Boron
aids in cell division and in transporting sugars
through cell walls. It also aids in forming the
amino acids thymine and cytosine, important to
DNA synthesis.
The B-deficient leaves show a light general
chlorosis. The tolerance of plants to boron
varies greatly, to the extent that the boron
concentrations necessary for the growth of plants
having a high boron requirement may be toxic to
plants sensitive to boron. Boron is poorly
transported in the phloem of most plants (affects
new growth first), with the exception of those
plants that utilize complex sugars, such as
sorbitol, as transport metabolites. The
B-deficient causes "Heart rot" in beets and "stem
crack" in celery.
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Molybdenum (Mo)
Molybdenum (Mo) a catalyst needed in small
quantities. It is involved in nitrogen fixation
(assimilation) and in the manufacture of enzymes.
The Mo-deficient leaves show some mottled
spotting along with some interveinal chlorosis.
An early symptom for Mo-deficiency is a general
overall chlorosis, similar to the symptom for
nitrogen deficiency but generally without the
reddish coloration on the undersides of the
leaves. At high concentrations, molybdenum has a
very distinctive toxicity symptom in that the
leaves turn a very brilliant orange. In the case
of cauliflower, the lamina of the new leaves fail
to develop, resulting in a characteristic
whiptail appearance (long, narrow and severely
twisted, but not tightly bunched).
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Abiotic Diseases (cont.)

• (II) Environmental
• (Sunlight, Humidity, Temperature, pH,
• Chemical addition, Rainfall, Soil texture)

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High temperature
D. deremensis 'Warneckii' is subject to
notching, a condition affecting marginal tissue
near the leaf base. This condition is apparently
due to high temperatures. Apical necrosis caused
by rapid increases in temperature in foliage
plants was first described in 1961. The tested
plants were not damaged at 15.5 or 35ºC (60 or
95ºF), but raising the temperature from 15.5ºC to
35ºC resulted in apical necrosis or blackening of
new leaves.
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Chilling temperature
The symptoms are characteristically
greasy-looking, water-soaked lesion, developing
within 48 hours of exposure and affecting old
leaves most severely.
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Cold damage
Cold or cool environments (2-8ºC) can severely
damage tropical plants. Temperatures that are
safe for many other crops cause some injury in
some foliage plant. Exposure to these
temperatures results the development of white,
sunken, irregularly shaped lesions. Cold injury
is more severe in plants receiving high levels of
nitrogen and potassium than in plants receiving
lower levels of these nutrients.
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Direct sunlight exposure
necrosis (burn and dead)
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Drought Injury
Drought can broadly be defined as a low water
availability that limits or prevents growth. The
severity of drought depends on the duration.
Symptoms of drought stress begin with a bluish
color, followed by leaf rolling and eventual
browning. Drought stress also can be observed as
localized dry spots that appear as irregular
patterns of dead and dying leaves.
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Excess fertilizer
When too much fertilizer is applied, the nutrient
balances in grass plants or soil systems disrupt
so, excessive growth is favored, which may result
in scalping damage (burn or desiccation of leaf
tissues).
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Pesticide Damage
Many pesticides used for weed control and
turfgrass disease control, and other pest
management chemicals, have growth regulating
properties. Misapplication of pesticides may
cause injury or irregular growth. Pesticide
injury is easily differentiated from disease and
insect injury. Generally the damage will appear
in a pattern that corresponds to the method of
application and includes broad to narrow streaks,
corresponding to overlapped application or other
regular patterns. Specific signs of this type of
injury include lack of pest control, turfgrass
chlorosis, leaf speckling and death. These
symptoms can develop quickly after application or
several weeks later.