Virus transmission in Amaryllid seeds?
totototo@telus.net (Fri, 11 Sep 2009 10:50:32 PDT)
On 10 Sep 2009, at 21:55, Tony Avent wrote:
unless the virus causes a significant problem such as disfigurement of vigor
loss, most folks never suspect a problem. It's only the plants that show
symptoms that cause gardeners to get upset.
The real issue isn't infection with this or that virus in particular, but the
gradual infection of a plant by a number of viruses. Individually, none of them
would amount to much of a problem, but as the virus titer goes up (i e when a
plant is progressively infected with an more and more viruses), vigor declines.
This is the usual explanation why old cultivars propagated by vegetative means
ultimately disappear or become so fussy to grow that only a few enthusiasts can
give them the attention they require to stay alive.
Tissue culture methods have been used to clean up a surprising range of plants,
ranging from show auriculas on the verge of extinction to Cosmos
atrosanguineus, formerly a very rare plant, today sold widely in 4" pots.
But there's an even more insidious problem: those vigorous plants that tolerate
viral infections and then act as typhoid Marys, infecting other nearby plants
via transmission by aphids, leafhoppers, and uncleaned garden implements.
There are some mysteries in the world of commercial bulb production. The little
narcissus 'Tete a Tete' is entirely virused, yet sold very, very widely. You
would think that someone would put it through tissue culture to rid it of its
virus(es), but evidently it has sufficient vigor as is that the producers can't
be bothered.
Another mystery is the horribly virused form of Crocus kotschyanus that is
sold. Its flowers are so deformed that it has no garden value at all, yet this
crocus is quite easy from seed, and seedlings reveal its true beauty. I always
thought of it as a rather small-flowered crocus until I obtained some seedlings
from a naturalized patch of it that has spread by seed.
If all you are growing is common garden plants, the issue of viral infection
can be ignored, but if you are growing species grown from seed, you must be
much more careful. One rule of wisdom applies to lily growers: if you wish to
grow the species from seed, then you must not grow any of the hybrids in the
Dutch bulb trade because they are one and all virused and will infect and
destroy the less robust species.
As for transmission by seed, I believe there are a few plants where this
happens, but for the life of me cannot recall which genus.
--
Rodger Whitlock
Victoria, British Columbia, Canada
Maritime Zone 8, a cool Mediterranean climate
on beautiful Vancouver Island