Download Symptoms of plant disease

Symptoms of plant disease
Types of symptoms
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Morphological symptoms (Externally symptoms)
(exhibited by whole plants or by any organ of a plant), detected visually or
through the senses (smell, taste or touch) are termed morphological
symptoms.
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Histological symptoms (Internal symptoms)
Detected by microscopically examination of diseased tissue.
Type of Morphological symptoms (Externally symptoms)
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Necrosis
Hypoplasia
Hyperplasia & Hypertrophy
Necrosis
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Necrosis: degeneration of protoplast followed by death of the tissue or
organ or plant.
Two type of necrosis:
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Plesionecrosis (Nearly dead): Necrotic symptoms expressed before the
death of the protoplast are called plesionecrosis. E.g. Yellowing,
Hydrosis, Wilting.
Holonecrosis: Necrotic symptoms expressed after the death of the
protoplast are called holonecrosis. In this the affected tissue turns
brown in color E.g. Rots, spots, blights.
Plesionecrotic symptoms:
_ Yellowing: Appearance of uniform or non-uniform yellowing of
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leaves due to infection. it is the result of breakdown of the chlorophyll
e.g. by fungi (e.g., celery yellows), viruses (e.g., sugar beet yellows
virus),
bacteria (e.g., coconut lethal yellowing),
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protozoa (e.g., hart rot), spiroplasmas or phytoplasmas
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_ Wilting: A symptom characterized by loss of turgor, which results in
drooping of leaves, stems, and flowers. e.g. Fusarium wilt of tomato.
— Pathological wilt: caused by pathogen-fungus, bacteria and
viruses
— Physiological wilt: due to water stress and high temperature
_ Hydrosis: Appearance of water soaked trnasluscent diseased tissues
whose intercellular spaces contains liquid. This type of symptoms precedes
holonecrotic symptoms
Holonecrotic symptoms
May develop on any part of the plant and generally the infected tissues turns
brown.
Holonecrotic symptoms can be divided into three categories
o Necrosis of the green plant parts
o Necrosis of the storage organs
o Necrosis of woody tissues
Necrosis of the green plant parts leads to formation of number of disease
symptoms like:
• Restricted necrosis
– Damping off: Is the collapse and death of seedlings due to extensive
necrosis of stem tissues before or after they emerge from the soil (preemergence and postemergence damping-off, respectively)
– Spots: A will defined or self-limiting grey, tan or brwon necrotic lesion on
a leaf
– Shot holes: When a necrotic tissue with in a leafspot cracks and fall off,
leaving small holes in their place.
– Blotch: A necrotic area covered with brown fungus mycelium on leaves,
shoots, and stems.
– Streaks and stripes: Streaks and stripes mainly occur in
monocotyledonous plants.
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Extensive necrosis
_ Blights: A disease characterized by rapid and extensive death (Necrosis)
of plant foliage.
_ Scald: Nonpathogenic necrosis of epidermal and sub epidermal cell (sun
scald).
_ Scorch: Necrosis around leaf margins.
_ Blast: It is sudden death of unopened bud or inflorescence.
_ Anthracnose: Purplish coloration resulting from over development of
anthocyanine pigments.
Necrosis of woody tissues:
_ Die back: Extensive necrosis of shoots from top/ tip to down ward e.g. die
back of citrus
_ Cankers: Formation of sharply delineated, dry, necrotic, localized lesions
on the stem due to death of cambium tissue of bark, or (in non-woody plants)
_ Gummosis: A plant disease in which the lesions exude a sticky liquid.
_ Guttation: Exudation of water from plants, particularly along the leaf
margin.
Necrosis of the storage organs
_ Rots: The softening, discoloration, and often decay or disintegration of a
succulent plant tissue as a result of fungal or bacterial infection.
_ Leak: Exudation of juice from tissues with soft rot is called leak
Mummification: Drying of the rotted organs resulting in shriveling and
hardening like mummies.
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Hyperplastic & Hypertrophic symptoms
Hyperplasia: A plant overgrowth due to increased cell division.
Hypertrophy: A plant overgrowth due to abnormal cell enlargement.
_ Tumors: An uncontrolled growth of tissue or tissues.
_ Galls: An abnormal plant structure formed in response to parasitic attack
by certain microorganisms (bacteria, fungi, viruses) or insects.
_ Witches Broom: An abnormal form of plant growth characterized by
profuse outgrowth of lateral buds to give a broom like appearance.
_ Enations: A symptom caused by certain plant viruses in which there are
small outgrowths on the plant.
Scab: Raised and rough lesion due to overgrowth of epidermal and under
lying tissues.
Virescence: The development of chlorophyll in tissues.
Hypoplastic symptoms: Failure of plant or organs to developed fully.
_ Chlorosis: The loss of chlorophyll from the tissues of a plant.
_ Atrophy/ Hypoplasis/ dwarfing/ Stunting: Failure of plants to attain full
size.
_ Rosette: In this the internodes do not enlarge and leaves are clustered like
petals of rose e.g. Peach rosette, ground rosette
_ Albication:
_ Mosaic: Appearance of dark green, light green pattern or sometimes
chlorotic areas on leaves due to virus infection.
Signs: there are some examples of signs.
 Mildew: the white powdery or downy growth of a fungus on leaves,
shoots, flowers, or fruits.
 Mold: the fuzzy growth of a fungus on a plant part.
 Mycelium: the thread like, weblike, or matlike growth of a fungus.
 Ooze: the amber or cream-colored drops of liquid containing bacteria,
the drip or seep from infected plant parts.
 Rust: the red, yellow, orange, or some time black fruiting bodies or
spore masses
seen on plants infected with rust fungi.
 Sclerotia: a hard, durable structure produced by certain fungi that
allows the fungus to survive in soil or plant debris for many years.
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