Viruses can cause a variety of symptoms in infected plants. External symptoms include chlorosis, mosaic patterns, mottleing, vein clearing or chlorosis, necrosis, ring spots, enations, stunted growth, and premature leaf shedding. Internal symptoms involve changes to parenchyma cells, xylem, phloem, and cell organelles. Symptoms can be localized to infection sites or systemic throughout the plant. Some viruses may cause latent, asymptomatic infections or symptoms can be masked for periods of time.

1. Symptomatology of Virus
infected Plants
By; Dr. Taswar Ahsan (Microbiology & Plant Pathology)

2. Symptoms
• Symptoms are defined as macro or microscopic modifications in form, color, size,
physiology, anatomy as a result of any pathogenic attack
• It can be external or internal
• The most evident symptoms are present on leaves
• Although viruses can attack stem, roots
• The most common symptoms of viral diseases are the retardation in development
• This results in plant dwarfism
• Almost all viral diseases results in reduction of growth and yield of plants

3. Types
• On the base of localization symptoms are divided in two types
• 1.Localized
• 2.Systematic

4. • 1. Localized
• Certain viruses cause local infection at the point of entry and this infection is called local
infection and the symptoms are called as Localized
• 2. Systematic
• When virus effect the whole plant it is known as systematic infections and the symptoms
are known as systematic symptoms

5. • Asymptomatic
• Many viruses can infect certain plants without development of evident symptoms
• These viruses are known as Latent Viruses and the host is called Asymptomatic
• Masking
• Plants that develop symptoms when infected by viruses remain asymptomatic for long
period of time
• This is called Masking

6. External Viral Symptoms
• 1.Chlorosis
• 2.Mosaic
• 3.Molting
• 4.Vein Chlorosis & Vein Clearing
• 5.Necrosis
• 6.Ring Spot
• 7.Enation
• 8.Stunting in Growth
• 9.Pre Mature shedding of Leaves

7. Chlorosis
• These symptoms represent the areas which become weakened in green color due to
either destruction / inhibition of chlorophyll synthesis

8. Mosaic
• These are irregular white
• Light green or yellow color areas mixed with normal green color of plant leaf

9. Molting
• It is an irregular pattern of light and dark areas present on the surface of leaves
• Some virologist considered it as equality to mosaic

10. Vein Chlorosis & Vein Clearing
• It represents the chlorosis in veins and in these results in destruction of chlorophyll in
veins
• As a result of these two symptoms the veins become lighter in color as compare to
normal green color

11. Necrosis
• These are common viral symptoms representing the death of cell and these are due to
local infection
• The areas of dead tissues are differentiating by the presence of dark brown border around
it

12. Ring Spot
• This represents the local infection in the form of spots

13. • 7. Enation
• These are the outgrowth present in the lower surface of leaf mainly on vein and midrib.
• 8. Stunting in Growth
• This result in dwarfism of plants but the morphology of plants remains normal.
• 9. Pre mature shedding of Leaves
• It takes place due to the formation of Abssisic Acid (ABA)

14. Internal Symptoms
• Followings are some internal symptoms
• 1.Changes in Parenchyma cell
• 2.Changes in Xylem
• 3.Changes in Phloem
• 4.Changes in Cell Organelles

15. • 1.Changes in Parenchyma cell
• These changes occur due to attack of mosaic viruses. Parenchyma cell become reduce in
size, intercellular spaces, reduced & cell shape disturb
• 2. Changes in Xylem
• In xylem gum like substance appears and block the xylem. This process is called
Gummosis. Sometimes bladder likes out growth are produced in xylem and block it. This
is called Tylosis

16. • 3. Changes in Phloem
• Changes in phloem disturb the food supply. Symptoms mostly appear in sieve elements
of phloem
• 4. Changes in Cell Organelles
• a)Increase formation of vacuole
• b)Concentration of cytoplasm disturbs
• c)Ribosome and endoplasmic reticulum become reduce in number
• d)Nuclei shape disturbs
• e)Abnormal morphology of mitochondria
• f)Cell division (mitosis & meiosis) are also affected