What are viral diseases?

Aug 09, 2022, 16:45 IST

Symptoms of viral disease:

(A) External symptoms

These symptoms may be restricted to some parts (local) or associated with various life stages (systemic). Following are the external symptoms:

(i) Stunting - Plant size is reduced.

(ii) Little leaf - It is the reduction in leaf size in rosette formation.

(iii) Leaf curling - Here leaf curling may occur.

(iv) Leaf rolling - Here leaf rolling occurs.

(v) Witches broom - Here the leaves become narrow giving broom like appearance to the plant.

(vi) Tumor formation - the tumors appear on roots and leaves.

(vii) Vein clearing - Here leaf veins becomes yellow.

(viii) Vein banding - The entire leaf becomes yellow but veins remain green.

(ix) Enation - Here growth occurs on the leaves and stems.

(x) Mosaic - In leaf, light green patches appear.

(xi) Mottling - Here yellow patches appear on leaves which may be accompanied by curling of leaves.

(xii) Yellowing - Here complete chlorosis (entire leaves become yellow) occurs.

(xiii) Virescence - Flower becomes green in colour.

(xiv) Ring spots - Here necrotic or chlorotic spots appear on leaves .

(xv) Phyllody - Floral parts are transformed into leafy structure.

(B) Internal symptoms:

(i) Phloem cells are degenerated.

(ii) Formation of tylose occur.

(iii) Callose formation occur.

(iv) Hyperplasia in Xylem and Phloem occur.

(v) Aggregation of mitochondria.

(C) Physiological symptoms:

(i) Change in permeability of unit membrane.

(ii) Amount of chlorophylls are decreased therefore rate of photosynthesis also decreases.

(iii) Amount of carbohydrate decreases.

(iv) Rate of respiration increases due increase in activity of respiratory enzymes.

(v) Necrosis occurs due to production of phenolics.

Common viral disease of plants:

(i) Tobacco mosaic (ii) Abutilon mosaic

(iii) Papaya mosaic (iv) Cucumber mosaic

(v) Potato mild mosaic (vi) Potato rugose mosaic

(vii) Tomato leaf curl (viii) Little leaf of bringal

(ix) Rosette of groundnut (x) Bunchy top of banana

(xi) Sugarcane mosaic

Common viral disease of man

Name of the virus	Causal virus
(i) Common cold	Rhinovirus
(ii) Influenza	Influenza virus
(iii) German measles (Rubella)	Rubella virus
(iv) Poliomyelitis (Polio)	Polio virus
(v) Small pox	Variola virus
(vi) Yellow fever	Arbo virus

Plant virus disease control

(A) Developing resistant varieties by

(i) Breeding to develop viral disease resistant variety of seeds.

(ii) Breeding plants for vector resistance.

(iii) Using antiviral substances of plant origin.

(B) Control of vectors

(i) Forecasting Aphid - borne virus disease.

(ii) Chemical control of insect and nematode vectors.

(iii) Chemical control of fungal vectors.

(C) Elimination

(i) Heat treatment of perennial plants to eliminate phytoplasmas, viruses and viroids while maintaining plant survival.

(ii) Virus elimination by meristem tip culture and tip micrografting. Biology Doubts page consist of more questions and answer related to this topic. 

What are viral diseases? pdf