Pumpkin Virus

Joe wrote saying he felt he had a virus last year but would like to use
the same garden plot for 1999:
He wrote:
> Two of my four plants last year had symptoms of a virus. It started in one of my plants and about 3 weeks later showed up in the adjoining plant. There was yellowing in the new growth leaves and the plants and fruit became stunted. I was cutting off all of the stunted new growth 
in an attempt to save my plant. I may have inadvertently passed the
virus on to the second plant because I was not sterilizing my shears as
I moved from plant to plant. I eventually pulled up both plants and took
the infected vines to an area far away from my garden.

Some people have recommended that I plow up a different area this
summer, because the virus may still be in the soil in my old garden. I
didn't want to do that, because I have spent a lot of time the past
couple of years building up my organic matter. My land is heavy clay
where I have not brought in tons of manure and soil additives. 

My question is, do you think it would be safe to use the same garden
area where the infected plants were or am I at risk the virus will show
up again this year if I do? 

At a recent pumpkin seminar I attended at Guelph, Ontario, Bill Greer
mentioned one of his plants had signs of a virus in 1997. He planted in
the same area in 1998 and in fact used seeds from the infected plant and
his garden was virus free. 

> The leaves on my infected plants looked exactly the same as the pictures illustrating cucumber mosaic virus in Don Langevin's book 
"How to Grow World Class Giant Pumpkin II". That's all I'm going by.
Thank you. Joe

End of Joe's message.
indbio@disknet.com replies:

My short answer is that soil borne virus diseases are somewhat uncommon
and many not be a problem. For strawberry they are a problem only in
Great Britian and the Pacific Northwest, but in Indiana we have a
problem with nematode carried virus disease in cereal grains. 

Now lets try a more definite answer. No plant viruses can infect plants
directly from soil. The soil borne viruses are mostly carried by
nematodes from one plant to another. Can any soil organism carry the
virus you had last summer to a crop this summer? Some vectors can carry
a virus only for hours or days, but nematodes tend to carry viruses
longer.
  I would begin by guessing which viruses you might have had and then
reading about each of those viruses. In your case the disorder looked
like cucumber mosaic virus. 
  First I would got to http://image.fs.uidaho.edu/vide/ and click a
button based on the info I have. I decided to look for cucurbit family.
and clicked on Host family, then Cucurbitaceae, then C. maxima, then
Cucumber mosaic cucumovirus, which takes me to the page about the virus.
I shall look for info about soil vectors of the virus and its
persistance in such vectors. 
  I notice there are several strains of the virus. That is a problem; I
will need to consider all the strains. Under natural host range and
symptoms; it says peristent symptoms (the plant symptoms last a long
time). Under cucurbits it says mosaics and stunting and reduced fruit
yield which agrees with what you told me. 
  Under transmission we see that nearly every aphid God created loves to
transmit CMV but in a non-persistent manor (an aphid is infective only
for hours--probably on his dirty lips). Nothing is said about nematodes
and I would not worry about soil transmission. 
  It does say CMV is variably transmitted in some species of seed.
Therefore I would try to check on whether cucurbits seeds can transmitt
the virus. I would do web searches using +CMV +seed     or   +virus
+seed +pumpkin, etc. 

It is not at all difficult to test for viruses in sap and AG growers
could consider do this. I have had all these seeds, but I am not sure
they are alive. I would normally be able to supply the Chenopodium seeds
free.

Diagnostically susceptible host species and symptoms 

     Chenopodium amaranticolor, C. quinoa - chlorotic local lesions. 
     Cucumis sativus - systemic mosaic. 
     Vigna unguiculata - necrotic local lesions. 
     Lycopersicon esculentum, Nicotiana &KHgr; edwardsonii, N. glutinosa, N.
tabacum -
     symptoms depend on virus strain. 
The above are lambsquarter
  cucumber, I use National Pickling rub sap into the cotyledons
  Cowpea
  tomato and tobacco
I will try to write webpages on these or find links with pictures. 
Local means the lesion occur only where you rubbed sap
Systemic means to spread throughout the plant, usually only to the new
young growth. 

I guess I would feel pretty safe growing AG again in the same plot. The
most likely problem will be infection from some source. 
  If CMV is a threat to AG growers then we need to look for sources of
infection. We should also try to compile a list of all the viruses which
are a commen threat to AG and make info available via our various web
pages. I have never had to worry about these viruses because they to not
attack small fruits. 
  The tobacco viruses attack many things and are pretty common, I would
read whether they attack AG. It is possible different AG strains have
differing resistance to viruses. 
  Some viruses overwinter on weeds and then aphids carry them to crops. 

-- 
Harold Eddleman Ph.D. Microbiologist.       i*@disknet.com 
Location: Palmyra IN USA; 36 kilometers west of Louisville, Kentucky
http://www.disknet.com/indiana_biolab



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