Virus Diseases of Dahlia
 
Dahlia Home
What are Viruses?
  What viruses do to plants?
Are there any 'good' viruses?
How are viruses named?
How are viruses identified?


 

Viruses of Dahlias
How do virus diseases look?
Important Dahlia Viruses
Virus Symptoms
How do Dahlia viruses spread?
How to control Dahlia viruses?
How important is vector control?
What help is available for virus identification?

 

 

ARE THERE 'GOOD' VIRUSES?

Not all viruses are bad. In a few cases the effect of a virus on the host may be prized. For example, variagation of flowering maple leaves and tulips is caused by infection with specific viruses (Fig.). Also, it has been known for many years that a mild infection of a plant can protect it from damage caused by more severe isolates of the same virus. This phenomina is known as ‘cross protection’. An example is the control of very damaging citrus tristezia disease in Brazil by inoculation of young trees with mild isolates of citrus tristezia virus. In the case of dahlias, cross protection is at present problematic because a virus strain may be mild in one cultivar but severe in another. Also some dahlia plants may already be infected by more than one virus and there are many examples of different viruses interacting in unexpected ways to cause severe damage. The cross protection mechanism is not well understood we do not know enough to employ it safely. It should be noted that cross protection does occur naturally sometimes.

 
                         
 
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