Dahlia mosaic
virus is aphidborne. Aphid transmission is not mearly the result
of virus contamination during feeding. Aphid transmission is so
important to the survival and success of the virus that the virus
carries a gene required for aphid transmission. The gene codes for
a protein known as a virus acquisition factor or helper component
which is needed bind the virus to the aphid during feeding. The
mechanism involved in aphid transmission is not well understood.
There has been some disagreement as to whether the virus-aphid interaction
is nonpersistant (acquisition and transmission lasting seconds to
several minutes) or semipersistant (retention of the virus for hours).
The mechanism influences the chance of virus introduction and chance
of spread of DMV. Also, the relative importance of aphid spread
of DMV is also questionable. We have reasons to believe that aphid
spread is relatively infrequent. We have cloned and sequenced 6
virus isolates from 6 individual plants all of which came from the
same region. All 6 isolates are distinct and not closely related.
Based on current understanding of virus epidemiology, if aphid spread
is common in a region, the virus isolates should be closely related.
It suggests that DMV is primarily spread by propagation of dahlias.
However, DMV is not like most plant viruses. We expected to see
strain differences because viruses that use reverse transcriptase
enzyme for replication have high mutation rates.
