Symptoms of Plant Viruses
Definition:
Symptoms: Symptoms are the expression of the diseased condition of the plant.
All most all virus disease seem to cause some degree of reduction in yield and the length of life of virus infected plants is usually shortened. The most obvious symptoms of virus infected plants are usually those appearing on the leaves but some viruses may cause striking symptoms on the stem, fruits and roots.
Symptoms:
I) External (Macroscopic) :
A) Local:
These are the symptoms produced at the site of artificial inoculation on leaves with virus.
i) Chlorotic Local Lessions: Infect cell loose chlorophylls and other pigments.
Ex. TMV on Cowpea host.
ii) Necrotic Local Lessions: Infect cell die.
Ex. TMV on Nicotina Glutinosa host.
iii) Ring Spot Local Lesions: Conist of central group of died cells near inoculated area (Necrotic ring) Ex. Potato Virus: On Chenopodium Amaranticolar host.
B) Systemic:
In almost all viruses of plant occurring in field, the virus is present throughout the plant.
a) Variegation (Colour Breaking):
1. Decolouration in patches on leaves.
2. Sharpness of boundaries.
3. Distribution and discolouration of lamina.
i) Mosaic:
Mosaic are characterised by light green yellow or white areas intermingled with normal green of leaves of fruit or of whitish areas are intermingled with the areas of the normal colour of flowers or fruits depending upon intensity or patterns of discoloration mosaic type symptoms may be described as follows.
a. Streak or stripe: Red stripe of jowar.
b. Vein clearing: BCMV
c. Vein banding: Beat curly top.
d. Inter veinal mosaic light discolouration restricted in bet. veins.
ii) Line Pattern:
a. Oak leaf pattern (OLP) ( Apple oak leaf)
b. Systemic Rings (AMV on tobacco)
iii) Mottling:
If the discoloured patch of a variegated leaves are rounded the variegation is usually designated as mottling.
b. Malformation
1. Change in leaf form, any deviation from normal.
2. This includes uneven growth of leaf lamina leaves becomes curled, britle ( Crinkling) and show, prominaces and depressions ( puckering) upward and downward curling, vein distortion, leaf enation, galls and tumours.
c. Others:
a. Reddening of leaves cotton red leaf due to abnormal accumulation of anthoecynamin.
b. Blackening of veins Potato virus ‘Y’ in potato (Due to more synthesis of melanis).
c. Bronzening: Ex. TSWV, in Tomato
d. Etching: Tobacco etch virus.
II) Internal (Microscopic):
These include inclusion bodies. Inclusions are microscopic bodies produced by some of the viruses. These are produced in cytoplasm or nucleic acid.
a) Cytoplasm:
1. Amorphous or amoeboid also called as X-bodies produced by spherical or oval viruses Ex. CMV.
2. Crystalline: These type of inclusions are produced by rod shaped viruses. Ex. Red clover vein mosaic, cactus virus, and petunia ring spot.
b) Nucleus:
Ex. Tobacco etch virus, rectangular plates. BCMV- Strain pisum Virus -2. Isometric crystals.
Proliferation (Toratonic symptoms):
1. Asymmetry of leaf lamina Ex. Grape fan leaf.
2. Blistering: Dark green area may be raised to give blistering effect. Margin of leaves twisted ex. BCMV.
3. Swelling of stem: Cocoa swollen shoot virus.
4. Flattening of branches and distribution of stem: Apple flat limb.
5. Enations: These are the out growth in different shape and form either on veins or leaf lamina.
6. Vein enation: Citrus onation virus, pea enation mosaic.
7. Leaf enation: Cotton leaf curl: Tobacco leaf curl;
8. Tumours: Clover wound tumour virus.
9. Galls: Woody galls of citrus.
10. Pitting: A) Stem pitting – Apple stem pitting, citrus twisteza virus on kagzi lime.
B) Fruit pitting: Pear stony pit- Apple groove virus on apple.
11. Stunt: Tomato bushy stunt.
12. Dwarfing: Barley yellow dwarf.
13. Leaf Roll: Potato leaf roll.
14. Yellows: Beet Yellows.
15. Pox: Plum pox virus.