Transmission of Plant Viruses

Transmission of Plant Viruses

• Plant viruses do not penetrate the intact plant cuticle, hence they are not disseminated by wind or water.
• Viruses are transmitted from plant to plant through various means, including:
  • Mechanical contact
  • Grafting
  • Vegetative propagation
  • Botanical (sexual) seed
  • Pollen
  • Common dodder
  • Vectors

Infection Inhibitors

• Inhibitors are found in many plants and decrease infection in inoculated plants.
• These substances act by:
  • Reducing the susceptibility of the host plant
  • Interfering with the infection process

Virus Particle Inactivators

• Quinones are formed by the oxidation of polyphenols as they come into contact with cytoplasmic enzymes during tissue maceration.
• Quinones are highly toxic compounds that:
  • Can destroy some proteins
  • Degrade virus protein subunits, exposing the nucleic acid to ribonucleases
  • Abolish virus infectivity with a single rupture in the virus nucleic acid

Grafting

• Grafting is a technique that involves placing cut tissue surfaces of different plants in close contact.
• Grafting is a universal method for transmitting viruses, particularly useful for:
  • Phloem-restricted viruses that cannot be transmitted mechanically
  • Viruses whose vectors remain unknown
  • Detecting viruses found in low concentrations
• Virus transmission by grafting may not be 100%-effective if:
  • The virus is unable to cross the graft union
  • The virus source plant was not totally invaded and the portion used was virus-free due to irregular virus distribution
• Successful virus transmission depends on:
  • Characteristics of the virus
  • Union achieved through grafting
• Types of grafts:
  • Side grafts
  • Wedge grafts
  • Approach grafts
  • Bud grafts