3. The intensity of plant viral infection depends upon
Virus strain.
Cultivars/ varieties of host.
Plant age.
4. 1. Virus Strain
Two different viral strains of same viruses may show different degree of pathogenicity.
A viral strain that can cause marked symptoms is known as Serve Strain and infection caused by
this strain is known as Serve infection.
Whereas other strains that cannot cause infection or show very weak symptoms. This type of
strain is known as Mild strain and infection is known as Mild infection.
5. 2. Cultivars
Different cultivars / varieties of same may show different dgree of symptoms by same virus.
Three types of cultivars are identified
Susceptible Cultivars
Resistant Cultivars
Tolerant Cultivars
6. a) Susceptible Cultivars
Susceptible cultivars can be infected and show symptoms for viral infection.
b) Resistant Cultivars
These cultivars cannot be infected by virus.
c) Tolerant Cultivars
These may become infected but it will not show the symptoms although virus is present in plant.
7. 3. Plant age
Plant age is an important factor for the degree of intensity of viral infection.
Young plants are more susceptible for infection as compared to older plants.
In some cases viral attack is Lethal in young plants. Whereas Non- Lethal in older plants.
9. These are about 450 species of pathogenic viruses which cause viral diseases in plants. The
plants are resistant to majority of pathogens. In plants there are two types are resistant are
present.
Preformed Resistance
Induced Resistance
10. 1. Preformed Resistance
This type of resistance is present naturally in plants it includes:
Plant Cuticle
Plant Cell Wall
Antimicrobial Chemicals
Antimicrobial Proteins
Enzyme Inhibitors
Receptors
11. a) Plant Cuticle
Almost all plants have cuticle which prevent the entry of pathogens.
b) Plant Cell Wall
Cell wall also provides resistance to plant cells against viral attack.
c) Antimicrobial Chemicals
Many plants produce antimicrobial chemicals which provide resistance against viral infections.
12. d) Antimicrobial Proteins
Several proteins are produce which can resist for entry of viral nucleic acid e.g. Thionins.
e) Enzyme Inhibitors
In plants enzyme inhibitors are present which can inhibit the enzyme activity required for viral
transmission.
f) Receptors
Receptors present on cell wall or plasma membrane can prevent the entry of virus in to host cell.
13. 2. Induced Resistance
The resistance which is generated after infection is known as induced resistance. It includes:
Cell Wall Reinforcement
Antimicrobial Chemicals
Antimicrobial Proteins
14. a) Cell Wall Reinforcement
After infection deposition of lignin, cutin, suberin and proteins increase which help in
resistance.
b) Antimicrobial Chemicals
After infection the concentration of many chemicals increases such as Hydrogen peroxide and
Phytolexin.
c) Antimicrobial Protein
These include Thionins and these are produced during viral attack and provide resistance to
plants against pathogenic infection.
