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Plant Disease Symptoms

Pl. Path. 111 (Cr. Hrs. 3+1)

P.N. Sharma

Department of Plant Pathology,

CSK HPKV, Palampur (H.P.)

symptom and Sign

Symptom – are the expression of the disease caused by the

manifestation of the physiological reaction of the plant due

to harmful activity of the pathogen

Sign - physical evidence of the presence of disease

agent (e.g., mold or fungal spores, bacterial ooze)

Syndrome

Defined as sequential appearance of disease symptoms on a plant during the development of the disease or sum total of symptoms exhibited by a disease

Fleck or necrotic spot

Uredial pustule

Telial pustule

Death of organ or plant

Local infection:

An infection affecting a limited part of a plant e.g. leaf

spot.

Systemic infection:

infection that spread point of infection to different parts

of the plants e.g. wilts, virus infection, loose smut

Lesion

A localized necrotic or chlorotic areas of diseased

tissue/ organ.

Local lesion:

A localized spot produced on a leaf upon mechanical

inoculation with a virus.

Types of symptoms

Morphological symptoms

Histological symptoms

• Morphological: (Externally detectable

symptoms caused by any pathogen e.g.

blight, leaf spot

– Necrosis

– Hypoplasia

– Hyperplasia & Hypertrophy

Morphological symptoms

Morphological: (Externally detectable

symptoms caused by any pathogen e.g.

blight, leaf spot

– Necrosis

– Hypoplasia

– Hyperplasia & Hypertrophy

Necrosis degeneration of protoplast followed by death of the

tissue or organ or plant

• 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 colour

E.g. Rots, spots, blights

Plesionecrotic symptoms

• Yellowing:

• Wilting:

• Hydrosis:

Yellows/ yellowing

Appearance of uniform or

non-uniform yellowing of

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),

protozoa (e.g., hart rot), spiroplasmas or

phytoplasmas

Wilt Browning of vascular tissues

Wilt: A symptom characterized by loss of turgor, which results in drooping of leaves, stems, and flowers. e.g. bacterial 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

– Necrosis of the green plant parts

– Necrosis of the storage organs

– Necrosis of woody tissues

• Necrosis of the storage organs

– Rots

– Leak:

– Mummification:

Necrosis of the green plant parts

leads to formation of number of disease

symptoms like:

• Restricted necrosis

– Damping off

– Spots

– Shot holes

– Speck or fleck

– Blotch

– Streaks

– stripes

Damping-off • Is the collapse and death of

seedlings due to extensive

necrosis of stem tissues before

or after they emerge from the

soil (pre-emergence and post-

emergence damping-off,

respectively).

•caused by Pythium and

Rhizoctonia ,

Leaf spot: A wll defined or self-limiting grey,tan or brwon

necrotic lesion on a leaf

Angular leafspot of beans

Septoria leafspot of tomato

Veinal necrosis and local lesions

BCMNV

Shot hole. When a necrotic tissue with in a

leafspot cracks and fall off, leaving small

holes in their place

Shot hole of Cherry: Coccomyces hiemalis

Purple Blotch of garlic:

Alternaria porii

Blotch: A necrotic area covered with brown fungus mycelium

on leaves, shoots, and stems

Streaks & Stripe

Maize Streak- MSV Barley stripe

Drechslera graminea

Necrosis of woody tissues

• Die back: extensive necrosis of shoots

from top/ tip to down ward e.g. die back

of chilli/ citrus

• Cankers: Necrosis of the bark tissues e.g.

citrus canker

• Gummosis: Oozing of gum like secretions

from the woody tissues: Gummosis of

stone fruits

• Guttation:

Die back: extensive necrosis of shoots from top/ tip

to down ward e.g. die back of chilli/ citrus

Canker:

• Formation of sharply delineated,

dry, necrotic, localized lesions on

the stem due to death of

cambium tissue of bark, or (in

non-woody plants)

Cankers

Bacterial canker of tomato

Stem canker Nectria canker on apple

Gummosis:

A plant disease in which the lesions exude a sticky

liquid.

ooze from bacterial canker (apricot) is milky in color

Guttation:

Exudation of water from plants,

particularly along the leaf margin

Extensive necrosis

• Blights

• Scald

• Scorch

• Blast

• Anthracnose

• Firing

Late blight of Potato

Blight:

• A disease characterized by rapid and extensive death (Necrosis)

of plant foliage.

• A general term applied to any of a wide range of unrelated

plant diseases. (e.g., chestnut blight, fireblight, late blight, halo

blight)

Bacterial blight of beans

Rice blast: Magnaporthe gresia

Blast : it is sudden death of unopened bud or inflorescence

Anthracnose:

Formation of discrete, dark-

colored, necrotic lesions on

the leaves, stems, and/or

fruits.

Caused by fungus:

Colletotrichum spp.

Bean anthracnose:

C. lindemuthianum Chili anthracnose:

C. capsici

Fire blight of apple: Erwinia amylovora

Necrosis of the storage organs

–Rots

–Leak:

–Mummification:

Buckeye Rot of tomato Rot:

The softening, discoloration, and often decay or

disintegration of a succulent plant tissue as a

result of fungal or bacterial infection.

Root & Fruit Rots

ROOT ROT

Leak: exudation of juice from tissues with soft

rot is called leak

Infected apple fruit exuding

droplets of fire blight

bacteria.

Mummification Drying of the rotted organs resulting in

shriveling and hardening like mummies

brown rot fungus (Monilia fructicola)

causes mummification the peach fruits

Hyperplastic & Hypertrophic symptoms

• Wound tumors,

• Galls

• Witches Broom

• Enations

Hyperplasia:

A plant overgrowth due to increased cell division.

Hypertrophy:

A plant overgrowth due to abnormal cell

enlargement.

Crown galls on peach; Agrobacterium tumefaciens

Gall:

• An abnormal plant

structure formed in

response to parasitic attack

by certain microorganisms

(bacteria, fungi, viruses) or

insects.

• Galls may develop either

by localized cell

proliferation or increase in

cell size.

Tumor: An uncontrolled growth of tissue or tissues

Crown gall/ tumor

Hyperplastic &

Hypertrophic

Hyperplasia:

A plant overgrowth due

to increased cell division.

Hypertrophy:

A plant overgrowth due to

abnormal cell enlargement.

Enation

A symptom caused by certain plant viruses in which

there are small outgrowths on the plant

Leaves of pea (Pisum sativum cv. Dark Skinned Perfection) infected

with Pea enation mosaic virus (PEMV)

Witches„ broom

An abnormal form of plant growth characterized by profuse outgrowth of lateral buds to give a broom like appearance.

Potato witches’ broom

Groundnut witches’ broom

Hypoplastic symptoms

• Atrophy/ Hypoplasis/ dwarfing/ Stunting

• Rosette: in this the internodes do not enlarge and leaves

are clustered like petals of rose e.g. Peach rosette,

ground rosette

• Albication: Complete repression of colour caused by

viruses, bacteria, fungi, and iron deficiency

• Mosaic; appearance of dark green and light green

areas on leaves e.g. Tobacco mosaic

• Chlorosis: failure of chlorophyll to develop fully.

Atrophy or stunting or Dwarfing

Corn stunt

• Chlorosis:

The loss of

chlorophyll from the

tissues of a plant,

resulting from

microbial infection,

e.g. viral infection, the

action of certain phytotoxins,

the lack of light, to

magnesium or iron

deficiency, etc. Chlorotic

tissues commonly appear

yellowish

Chlorosis & Chlorotic ring

spot by BCMV

Rosette:

An abnormal condition in which the leaves form

a radial cluster on the stem.

Groundnut rosettee caused by: Groundnut rosette umbravirus

Mosaic

BCMV

yellow mosaic

MYMV

Golden mosaic CpGMV

Mosaic:

Appearance of dark green,

light green pattern or sometimes

chlorotic areas on leaves due to

virus infection

Histological Symptoms:

(can be detected microscopic studies

of the disease sample/ tissue) also

called Pathological anatomy or

Morbid anatomy

e.g. Cuticle thickness, cell wall

degeneration etc.

Tylose formation in xylem

vessels due to wilt

General Disease symptoms

DOWNY MILDEW (Peronospora parasitica)

Downy mildew:

Formation of superficial cottony hyphal growth with

spores generally on under side of the leaf

Powdery Mildew

Apple scab (Fruit)

Apple scab (Leaf)

Scab:

roughened, crust

like diseased area on the

surface of a plant organ

(e.g., apple scab, potato

scab, wheat scab).

COMMON SCAB (Streptomyces species)

Vein clearing a) and Chlorotic ringspot (b) symptoms due

to BCMV in common bean

a

Vein clearing: A symptom of virus-infected leaves in which veinal tissue is lighter green than that of healthy.

Epinasty:

Downward curling of a leaf blade resulting

from more rapid cell growth on the upper side

of a petiole than on the lower side; often a

hyperplastic symptom of plant disease

Green Vein banding

Vein banding:

A symptom of virus-infected leaves in which tissues along the veins

are darker green than other laminar tissue.

Golden mosaic of cowpea

Leaf curl of tomato

Ergot:

• Sclerotia that replaces the grain in a diseased

inflorescence

• Disease of certain grasses and cereals,

especially rye, caused by Claviceps purpurea

Honeydew stage

Typical Leaf roll of lower leaves

Smut:

Appearance of masses of dark, powdery, and

sometimes odorous spores on inflorescence

e.g. stinking smut of wheat, common smut of

maize.

Mold :

A downy fungal growth on rotted or decaying

host tissue, usually consisting of mycelium.

e.g. grey mold of chickpea

White Mold/ rot of

Beans

Rust

Rust A disease giving a “rusty” appearance to a

plant and causal agents form rust-colored spores

Pustule Small blister-like eruptions on the leaf epidermis

created by spores formed underneath and push outward.

WHITE RUST (Albugo candida)

Ring spot:

Appearance of single or concentric rings of

discoloration or necrosis, the regions between

the concentric rings being green. The center of

the lesion may be chlorotic or necrotic

b

Stem-pitting: A

symptom of some

viral diseases

characterized by

depressions on the

stem of the plant

Stem pitting in

apple

Sooty mold:

Appearance of dark, spongy, hyphal mats on the

surfaces of certain plants due to organisms that

grow on honeydew.

Dodder infection

Scorch: "Burning" of leaf margins as a result of

unfavorable environmental conditions (high temperature)

Iron Deficiency

Acknowledgements

• I gratefully acknowledge the use of some very

important photographs given in text book

“Plant Pathology” by G N Agrios.

• I also acknowledge the scientists who spent

valuable time in generating information on

various aspects of plant pathology and

displayed the same on internet for use by

students, teachers and researchers

• Lecture dedicated to respected “G N Agrios”