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Re: HYB:Colchicine

> With all of the tetraploid bearded irises available today, with all the
> genetic material they bear (including genes for variegated foliage), it
> seems an uneccessary risk to use this hazardous compound to attempt the
> conversion of diploids to tetraploids.  Breeders have, in fact, been far
> more successful moving genes from diploids to tetraploids by careful
> breeding.  Colchicine is not a "magic wand" that automatically converts
> diploids to tetraploids.  

I agree that colchicine is not a "magic wand" and that it is quite
toxic. There is no known antidote. 
As for there being ample genetic material with tetraploid bearded
irises, there's room for debate. Bearded irises are not my bag, but I
read enough to know that there are still many improvements to be made.
Just perhaps, that genetic material is lurking out there in some diploid
that got left behind in the Great Bearded Diploid to Tetraploid Rush. In
both  Siberian irises and daylilies, there has remained a place for both
diploids and tetraploids and conversions are frequently done. Such is
not the case with bearded irises. It may be (past) time to reconsider.
As for the unnecessary risk, I do not agree. There are toxic substances
with a much higher risk of poisoning (due to toxic fumes) that are used
quite safely on a daily basis, both in the home and in industry. To
scare a would be scientist or hybridizer away from conducting those
experiments based on colchicine toxicity would be a shame. As for the
probability of a success in its use, it's no worse than hybridizing, IF
you really have a critical eye on your results. 
It is true that other chemicals with a much better animal safety profile
have been used for tetraploid conversion, but at this point, their
efficacy is still in question.

> This is undoubtedly due to the deadly consequences for both plant and animal
> cells of cochicine's action in halting cell division.  Only in the very few
> cases in which cell division begins again will the plant survive.  And even
> in these cases, the conversion to tetraploidy may be only partial, resulting
> in a plant that may soon revert to being diploid--colchicine-converted
> plants are notoriously unstable.

Most of the methods of using colchicine are rather crude, failing to
address the delivery of the chemical to the place it needs to be. Sam
Norris tried to address these issues in his 1997 article, while staying
in the scope of the amateur hybridizer. McEwen attributes his high death
rate to the death of the extremely sensitive growing root. He observes
that if new roots do not form, the seedling will die. I think McEwen's
observation suggests that a method to treat the seedling without harming
the root should be developed. This could result in a chimera where the
apical meristem, or a significant part of it converted. 

> What I am trying to say here is that working with colchicine is dangerous
> and the success rate is low.  Even the successes may evaporate after a while
> as the unstable chimeras go back to being diploids.  Please carefully weigh
> the dangers against the potential benefits before buying and using this
> chemical.

I would like to think that there are some people out there who are
willing to deal with the odds and the risks. I don't think working with
colchicine is any more dangerous than growing digitalis in your garden.
Digitalis is not for the novice gardener and colchicine is not for the
novice breeder.

> I sincerely hope that those of you planning to use colchicine without
> previous experience or instruction will reconsider your plan.

And I sincerely hope that those of you planning to use colchicine learn
to use it safely and come up with the best irises that the world has
ever seen.

R. Dennis Hager
on Delmarva


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