DO VIRUS DISEASES LOOK AND WHAT DAMAGE DO THEY CAUSE?
Viruses cause a wide range of symptoms and damage. Symptoms include
occasional yellow spots or blotches, mosaics, vein yellowing, yellow
line patterns, leaf margin yellowing and necrosis. Plants and roots
may be stunted, deformed in shape, leaves may role or cup and blossoms
and tubers may be suppressed in size and number. Often virus symptoms
can be confused with mineral deficiencies, other cultural problems
and insect damage. However, viruses very rarely rot or outright
kill their host. Virus names often imply a specific type of disease
symptom but in practice many different symptoms can be found with
of specific viruses based on symptoms is difficult because of the
variable nature of symptoms. Some of the reasons for symptom differences
- There are
multiple strains of most viruses. We have isolated 5 strains of
DMV so far that cause anywhere from no symptoms to severe mosaics
- Many dahlias
appear to be infected with 2 or more viruses. Virus mixtures can
affect symptoms from reduction in symptom severity to a synergistic
- Not all
dahlia viruses have been identified or they have been miss-identified.
For example, DMV has been considered a strain of Cauliflower mosaic
virus but our DMV samples are not strains of the latter but a
dahlia cultivars can differ in their susceptibility to any one
virus. A virus isolate that causes no symptoms in one dahlia may
be devastating to some other dahlia.
conditions (temperature, soil fertility, day length, moisture
etc.) can influence symptom severity. Therefore, a range of symptoms
can be found during the season on each infected plant.
severity and type are affected by stage of plant growth at time
of initial infection. Generally, the earlier the initial infection
the more severe the symptom. Initial infections that occur late
in the season often are minimal but tubers may still carry the