Plant Disease Symptoms - Pl. Path. 111 (Cr. Hrs. 3+1) P.N. Sharma Department of Plant Pathology, CSK HPKV, Palampur (H.P.)

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 symptoms
• Morphological:    (Externally detectable
  symptoms caused by any pathogen e.g.
  blight, leaf spot
   – Necrosis
   – Hypoplasia
   – Hyperplasia & Hypertrophy

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

Browning of vascular tissues     Wilt
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 ,

Angular leafspot of beans

                                    Septoria leafspot of tomato

Leaf spot: A wll defined or self-limiting grey,tan or brwon
                 necrotic lesion on a leaf

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

Blotch:
A necrotic area covered with brown fungus mycelium
on leaves, shoots, and stems

 Purple Blotch of garlic:
    Alternaria porii

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

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)

                        Late blight of Potato

Bacterial blight of beans

Blast : it is sudden death of unopened bud or inflorescence

        Rice blast: Magnaporthe gresia

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:

Rot:          Buckeye Rot of tomato
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
Hyperplasia:
A plant overgrowth due to increased cell division.

Hypertrophy:
A plant overgrowth due to abnormal cell
enlargement.

  • Wound tumors,
  • Galls
  • Witches Broom
  • Enations

Tumor:
  An uncontrolled growth of tissue or tissues

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   Crown galls on peach;
  proliferation or increase in    Agrobacterium tumefaciens
  cell size.

Hyperplastic &
       Hypertrophic
Hyperplasia:
A plant overgrowth due
to increased cell division.

Hypertrophy:
A plant overgrowth due to
abnormal cell enlargement.

    Crown gall/ tumor

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            Chlorosis & Chlorotic ring
  magnesium         or      iron
  deficiency, etc. Chlorotic
                                        spot by BCMV
  tissues commonly appear
  yellowish

Rosette:
An abnormal condition in which the leaves form
a radial cluster on the stem.

Groundnut rosettee caused by: Groundnut rosette umbravirus

yellow mosaic
                                            MYMV

  Mosaic
  BCMV
Mosaic:
        Appearance of dark green,
light green pattern or sometimes
chlorotic areas on leaves due to
virus infection                     Golden mosaic CpGMV

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:
Formation of superficial cottony hyphal growth with
spores generally on under side of the leaf

             DOWNY MILDEW (Peronospora parasitica)

Powdery Mildew

Apple scab (Fruit)

                    Scab:
                           roughened,   crust
                    like diseased area on the
                    surface of a plant organ
                    (e.g., apple scab, potato
                    scab, wheat scab).

Apple scab (Leaf)

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.

White Mold/ rot of
       Beans

Mold :
A downy fungal growth on rotted or decaying
host tissue, usually consisting of mycelium.
e.g. grey mold of chickpea

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)

b
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

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”