General Symptoms of Plant Diseases

1. Symptomatology (Part I)
Plant Pathology
(For U.G. & P.G. Students)
Dr.PoojaSingh
M.Sc. (Biotechnology), Ph.D.Botany

2. Important terms:
• Symptoms refer only to the appearance of diseased
plants or plant tissues, like chlorosis, necrosis.
• Syndrome: Series of symptoms.
Example: Fleck or necrotic spot
Uredial pustule
• Signs: The pathogen grow and produce a variety of
structures like mycelium, conidia, spores, fruiting body
etc., on the infected surface of host.

3. Infection
• Local Infection: An infection affecting a limited part of plant.
e.g. Leafspot
• Systemic Infection: Infection that spread from point of infection to
different parts of the plants.
e.g. wilts, virus infection, loose smut
Types of Symptoms:
1) Morphological Symptom
2) Histological Symptom

4. Morphological Symptoms
• Symptoms which are clearly evident on the body of the
host
1) Necrosis (Killing of plant tissue)
2) Hypoplasia (Under-development; stunting)
3) Hyperplasia or hypertrophy (over-development)

5. Cytological Symptoms
• Can be detected (microscopic studies of the disease
sample/tissue) also called pathological anatomy. e.g Cuticle
thickness, cell-wall degeneration, tylose formation etc.
• The viral pathogens that cause cytological are usually called “
latent viruses” and the respective hosts are called
“symptomless carriers”. Such symptoms are called “Masked
Symptoms”.

6. • Death of cells, tissues and organs as a result of parasitic activity.
• All type of pathogens cause necrosis (fungi, bacteria, viruses)
• Viral symptoms occurring in localized area.
• Besides viral necrotic symptoms, the fungal and bacterial pathogen cause
a variety of necrotic symptoms on their host.
NECROSIS:

7. • Green leaves, floral parts and fruits.
• Well defined localized (restricted) areas of
usually brown or tan necrotic tissue.
• Tiny spots are called “flecks” or “specks”.
• Dark threads of fungal pathogen on
surface of spot the symptom is called
“blotch”.
2 types of fungal leaf spot.
1) Tar-spot
2) Shot-hole

8. 1) Tar spots: raised and black-coated
tar on leaves caused by Phyllachora
and Rhytisima fungal pathogen.
2) Shot hole: Dead and collapsed
tissue in localized lesions shrink and
fall off. e.g Cercospora
Bacterial leaf spot: Bacteria invade the host leaf through
stomata and cause necrosis.
e.g. Leaf spot of mango

9. • Blight (burnt appearance) represents general and rapid
browning of infected plant parts primarily and then its
rapid and extensive death.
• Dead tissue give burnt or scorched appearance.
• Example: Late (Phytophthora infestans) and,
Early blight of potato (Alternaria solani)
Bacterial blight of rice (Xanthomonas compestris)

10. Blast
• Blast represents the sudden death of unopened buds and
inflorescence; the blasted organs are usually shed off the
plants

11. Scorch
• Scorch resembles blight, but the scorch occurs in
irregular patterns usually along the margin of leaves
and sometimes between the veins.
• Example of scorch is elm leaf scorch disease caused
by fastidious vascular bacteria.

12. Canker
• Canker (dead area in the bark or cortex of the infected plant) represents a localized
wound or necrotic lesion of the bark.
• Cankers generally begin at a wound or a dead stub.
• From that point they expand in all directions but much faster along the main axis of
stem, branch or twig.
• Examples: Nectria canker disease of apple
Cytospora canker of peach
Citrus canker (Xanthomonas compestris)

13. Die-back
• Severe necrosis of twigs or branches beginning at tip and
advancing towards their bases is called “die-back” or
“staghead”.
• Example: Die-back disease of chillies
(Colletotrichum capsici)

14. Damping-off
• Rapid death and collapse of seedling tissues near the soil
line resulting in the fall of the seedlings on the ground.
• Example: Damping off seedlings (Pythium spp.)

15. Anthracnose
• It is a sunken ulcer-like lesion of necrotic cells on infected
part of the host plant.
• Example: Mango anthracnose
(Colletotrichum gloeosporioides)

16. Streak and Stripe
• Streak represents elongated necrotic area along stems
and leaf-veins.
• Stripe is also elongated necrotic area but confined to leaf-
tissues between the veins particularly in monocotyledons.

17. Ring spots
• Common symptoms produced by viral pathogens.
• Chlorotic but mostly necrotic rings on the leaves, also
on the fruits and stem.
• Concentric ring spot on infected parts of the host plant.
Example: Tobacco ring spot and Tomato ring spot

18. Rot
• Rot represent dead and
decomposed tissue on various
parts of the host plant.
• Rotting may result due to non-
parasitic causal agencies, mainly
caused by fungal or bacterial
pathogens.
• Root rot, foot rot, stem rot, bud rot,
rhizome rot, ear rot, leaf rot, tuber
rot.
• Rots may be dry or soft.

19. Wilt
• Wilt is usually a generalized secondary symptom in
which leaves and shoots loose their turgidity, become
flaccid and droop (wilt) because of plugging of xylem
vessels of the root or stem either by the pathogen itself.
• Example:
1) Wilt disease of Arhar (Fusarium oxysporium)
2) Bacterial wilt of solanaceous crop

20. Scab
• Scabs are rough, crust like localized lesions or sunken
and cracked giving scabby appearance.
• They can occur on every part of host.
• Example: Scab disease of apple (Venturia inequalis)

21. Rust
• Rusts are small pustules of spores, usually breaking
through the host epidermis.
• Relatively small local areas of various colours on leaves
and stem.
• Basidiomycetous fungal pathogen.
• Examples: Black rust of wheat
(Puccinia graminis tritici)

22. Smut
• Smuts refer to shooty or charcoal-like powdery mass
usually appearing on floral organs, particulary the
ovary, though also on leaf, sytem and root.
• Basidiomycetous fungal pathogen
Example: Loose smut of wheat (Ustilago tritici)

23. Mildews
• Mildews represent the chlorotic or necrotic areas usually
covered with vigorous growth thereupon.
• Downy mildew in which the chlorotic or necrotic areas on the
host surface are covered with extensively growing
sporangiophores.
• Oomycetous fungal pathogen.
Example: Downy mildew of peas (Pernospora pisi)

24. Powdery Mildew
• Chlorotic and necrotic areas are covered with superficially
growing mycelia and fructifications of the pathogen giving
a dusty or powdery appearance usually of white and grey
colour.
• Ascomycetes fungi
• Example: Powdery mildew of peas
(Erysiphe polygoni)