Virus transmission in Amaryllid seeds?
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…

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