Lee Poulsen
Mon, 20 Nov 2006 12:18:22 PST
The problem with this is that it is a fairly difficult and 
time-consuming method, and therefore I'm sure, a very expensive method. 
So companies are probably unwilling to use it on all their various 
varieties. Usually it is used for those types of crops where a lot of 
money is involved. For example, the citrus industry depends on this 
since it involves a lot of money.

It is not just tissue culture. The method is based on the fact (?) [I'm 
not a botanist] that, if the temperature is high enough, the virus 
cells themselves travel much more slowly within the plant structure. So 
at the growing tips of plants, as the new cells are made, if the 
ambient temperature is maintained high enough, these new cells are 
virus-free for some amount of time before any viruses can travel to the 
new cells and infect them.

So what is done, at least with citrus trees, is that the entire plant 
is grown in a facility where the temperature is maintained at an 
elevated level 24 hours a day. This temperature is around 40°C (104°F). 
After growing for a number of days or weeks at this temperature, a 
person goes in and cuts the very very tip of the growing tips, and then 
those cells are put into tissue culture to produce new plants that are 
clones of the old plant minus the virus.

Once that is done as long as the new plants are kept virus-free, any 
sterile method of propagation can be used to mass produce any number of 
virus-free versions of that cultivar.

So it's that initial work that must be done that makes this method not 
the easiest or cheapest. The state of California has a facility that 
specializes in doing this for new cultivars of citrus varieties that 
are imported from other countries. The citrus industry is too important 
to allow it to become infected in any way by the introduction of 
viruses from infected imports. So I guess they're willing to fund such 
a facility. I don't know how much effort and cost the Dutch or any 
other bulb growers are willing to invest in.

--Lee Poulsen
Pasadena, California, USDA Zone 10a

On Jan 1, 1990, at 12:21 AM, John Bryan wrote:
> I am surprised no one has mentioned, in regard to virus in Hippeastrum
> and, for that matter, other plants, tissue culture. Vast numbers of
> growers use this method to get rid of virus in plants. Hadeco, as an
> example, use this method to clean a stock. Those of you who have 
> visited
> the labs on the farm just outside Johannesburg, will no doubt recall 
> the
> great number of plants being propagated this way. After the initial
> treatment, the new plants are grown on in, more of less, sterile
> conditions in a special greenhouse. Hadeco perform this work, under
> contract, for many growers in Europe. To say that all stocks are
> infected I feel is not only not true but unfair. Growers in the
> Netherlands are very conscious of the need to sell only the best
> possible stock. Cheers, John E. Bryan

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