Virus treatment

Kenneth Hixson
Thu, 15 Apr 2004 14:50:10 PDT
Mary Sue, everyone
>We have discussed virus many times on this list and the consensus always 
>seemed to be that throwing out virused material was the only way to go. 

	When I was a student at Oregon State University (many years ago),
one of the research projects was to heat treat material of Daphne odora,
which is mostly heavily virus infected.  Supposedly they had succeeded, or
at least thought they'd succeeded, in getting rid of virus, though I've 
not heard any more about it.
	Also, many lilies are now micropropagated (tissue cultured) in an
effort to rid them of virus.  "Enchantment", discussed recently, is one
cultivar which had ceased to be grown because of virus, was tissue cultured
and re-released as virus free.  Since lilies can be re-infected fairly
it is hard to know how long a lily will remain virus free, even if it was
"cleaned up".
	The following  paragraph is from Judith Freeman's hand-out on tissue/
embryo culturing lilies; the entire article appeared in the NALS December
2001 QB.  
This has been handed out numerous times, both at classes sponsered by the NALS
(North American Lily Society), and with the catalog from the Lilygarden.

	"How do we "clean up" a clone with tissue culture? 
	"With very small explants, a hopeful heart, and repeated testing! The
early theory was that the actual meristem, the little clump of
rapidly-dividing cells within the shoot tip, had not been invaded by virus
particles, so that we could remove it carefully and start a 'clean' plant
from it. Unfortunately, it takes a bigger clump of cells than just the
meristem to get a culture going. Different viruses replicate at different
rates depending upon many factors, so that by making lots of starts from
very small pieces, some of them will not contain enough virus particles to
sustain the infection. A variety of interventions can help reduce the
replication of virus particles of particular viruses in particular plants.
Sometimes it takes a long, long time for a very low level of infection to
build up to detectable levels, so that repeated ELISA tests are necessary
to be sure that the mother stocks are really clean. At present, we can only
test for viruses we have isolated, and if their protein coat changes, an
ELISA test will be negative even if the viral RNA is there."

	This same process is possible with other plants, but is
expensive--especially the
repeated Elisa test to determine if the virus is present.  I believe an
ELISA virus
test runs from $50 to $200 per test, depending on how many viruses are
being tested for.
Each type of plant requires slightly different hormone levels, etc, for
tissue culture,
so it takes experimentation for each new type of plant.
	I have seen plants offered of (supposedly) virus free Narcissus Peeping Tom
and N. Tete-a-tee, but they don't stay virus free very long.  However, the
is that there is some treatment available which at least strongly reduces the
virus in these plants.  Possibly the heat treatment already discussed?
	There are a lot of changes happening in this area, and new treatments will
undoubtedly emerge in time.

	Ken Z 7 western Oregon

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