Re: CULT: IRIS VIRUS (Rather windy )
From: John Montgomery <monashee@junction.net>
On Thu, 16 Mar 2000, you wrote:
> From: "Patrick Orr" <PatrickJOrr@hotmail.com>
>
Patrick, I have little knowledge specific to viruses in
iris but have more experience than I wish I had with virus
in lilium. I believe that it is reasonable to assume that
much of what we know about viruses in plants can be
generalized across genera. A caveat - I am not a
virologist and I am writing this with reference to memory
only, and that memory is showing signs of deficiency.
In Lilium, there are three major virus diseases and several
of lesser importance.
Tobacco mosaic virus (TMV) usually
shows as a mottling or streaking in the foliage.
Color breaking virus (CBV) produces a segregation of
colors in the tepals so that a pink flower might have
patches of near white with streaks of dark pink or red. It
generally is as ugly as sin and I don't think that is just
my opinion. I have never known anyone to admire the result,
even if they had no notion that it was caused by a virus.
Lily symptomless virus (LSV) as the name suggests shows
little in the way of symptoms except that the bulb
gradually loses vigor.
The names usually indicate the genus in which the virus was
first discovered. Until recently it was pretty much
assumed that TMV was the same thing whether in tobacco,
tomatoes or lilies. Recent evidence casts some doubt on
that. It was long thought that CBV originated, or was
first identified, in Rembrandt tulips and spread to other
genera. Now, however, reseach from Holland indicates that
CBV in lilies is not the same as CBV in tulips. So don't
chuck out your tulips if you grow lilies.
> If you can use the cultivar as the pollen parent and
>produce seedlings with the same markings then I guess you
>would have a genetic situation.
Perhaps not. Just recently, I have been informed by Dr.
Igor Cernohorsky in the Czech Republic, that virus can be
transmitted through pollen. I do not know if any
replication of this study has been done.
> I don't have an answer to your second questions
>John...sorry.
I guess this is the question of passing on viruses through
vegetative increase. The answer is yes. The virus can
even be transmitted on pruning or cutting tools.
Distinguishing CBV from genetic broken color - there is
probably no definitive visual rule. If you grow AZ AP you
may notice some small sort of tear drop darker spots in the
falls. I have noticed this in a few other IBs but the
names do not come to mind. This is a symptom of CBV. See
photos in TWOI p345. Arilbreds tend to show rather
irregular dark streaks.
If the virus can by transmitted through pollen, it is
likely that the only conclusive test is a lab assay.
Unfortunately this is not a very cheap test to have done.
> While we are on the subject, I thought I'd post a few
>questions...
> Does a virus effect performance, blooming, or
>propagation?
Wishy-washy answer - it depends. Some species and
cultivars will be seriously weakened and look quite ugly
while others can harbor a major infection and never
exhibit any symptoms nor lose any vigor or beauty.
A side effect of a virus infection may be that the plant
becomes more susceptible to other diseases such as botrytis.
> Isan iris with a virus really a bad thing?
Wishy-washy answer # 2 - it depends on the gardener. Some
take it as a personal affront to find that their plants
have any diseases, others will be more relaxed about it.
My own position is rather tolerant of virus. I will always
rogue out a lily with CBV because it offends my eyes. I
suspect that any garden which includes several cultivars of
lilies or arilbreds, for example, will have viruses present
in at least some of the plants and possibly in all of them.
It is also likely that if you propagate your strawberries
from your own plants for several years, they will be
virused and fruit production will decline in quality and
quantity.
As a lily breeder, I want to have virus in my garden (wish
every wish was as easy to achieve ;-) ). If I were to
breed lilies in a sterile situation, I would have no notion
of the resistance or tolerance of the seedlings. In theory
at least, over time the breeder can select parents for
their disease tolerance or resistance and with luck and
planning produce strains of tough plants. I have even
deliberately innoculated bulbs with virus to assess their
tolerance. On the other hand I would never use a pretty
flower on a plant which showed little tolerance to virus
for hybridizing. Pretty flowers are a dime a dozen but
tough plants are much harder to find.
I have begun to dabble a bit with arilbed hybridizing and
one of my aims is to find ABs which tolerate viruses well.
This is a side venture and may never get my full attention.
> What is the scientific name for this virus?
I don't know. generally in the literature they will be
referred to as CBV etc.
> Who is the person that proved a virus is the cause of these
markings?
Dr. Joe Q. Scientist, I guess.
> Is this virus contageous to other irises around it or to
humans?
Probably yes to other irises but not to humans.
> I haven't read anything in the current or past
>AIS bulletins that I have managed to get my hands on that
>discusses this.
There is a brief discussion in TWOI by John Weiler. It is
fairly well out of date by now (although not necessarily
incorrect.)
------------------------------
Some general notes.
Aphids are by far the most import vector for spread.
There is little in the way of effective aphid control
available to the home gardener. There are lots of things
which will kill aphids but if they carry a virus, the
infection will almost certainly have occurred before they
have been killed. Systemic insecticides will kill aphids
only after they have penetrated the leaf and after
transmission of the virus. I just use a strong stream of
water from a hose.
I know of no viricide which is effective so forget the
sprayer.
As a general rule, viruses will not be transmitted through
dried seeds. There are, however some trees which do
transmit virus. Possibly this may depend on a large
amount of endosperm which does not get dried.
Another general rule is that viruses will only survive in
living tissue. This makes control difficult because it is
in the best interest of the virus that it not kill it's
host. To do so would be suicide.
There is an interesting aside to this. some years ago, a
tobacco virus was found in the wild in Central America
which killed the immediately surrounding plant tissue
producing a bunch of necrotic spots on the leaf. This
proved to be a barrier to it's further spread. I believe
this eventually proved useful in commercial tobacco
production. I can probably dig out the reference but
right now I am writing off the top of my head.
Most viruses have a fairly narrow range of temperatures in
which they will survive ( I am talking of highs not lows.)
It has been reported that a lily bulb can be cleaned of
virus with a bath in water at a temperature of 45 C. (that
number is close but may not be precise memory.)
Tissue culture can also remove viruses
Viruses do not travel very quickly through plant tissue.
As a result meristem propagation from plants in a rapid
stage of growth, will usually be free of virus. My
experience in scale propagation of lilies is that if the
bulblets are removed from the scale when they are smaller
than a match head, they will usually be free of virus.
What To Do?
If your interest is in growing a garden only, then I
suggest that you relax and roll with the punches. If a
virused plant offends your eye, get rid of it. In all
liklihood there will be viruses present in other plants
which are tolerant so there will still be a source of
infection. If you can live with the symptoms, do not get
into a panic.
Keeping aphid populations low will help but I don't think
chemical warfare will produce any useful results.
At our place, the plants which is always loaded with aphids
are the Lupines. I once toyed with the idea of
interplanting lupines among lilies in the field rows with
the idea of attracting aphids and then using a systemic on
the lupines only. A closer look showed me that the aphids
which went to the lilies were not the same ones which
favored lupines. Another wild idea shot down :-(
The presence of virus has now been established in Hosta.
This could produce some real problems in identification.
If you grow a Hosta with rather streaky and unstable
variegation, I would at least suspect that virus may be
there.
By now I have completed my memory dump and exhausted your
patience.
Cheers
John Montgomery
Vernon BC Canada
Zone 5
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