Colchicine?

[Heather]

Can someone explain this? I know it has to do w/ increasing the ploidy. But what is it?

[Jmoney]

Colchicine is a mitotic inhibitor--arrests dividing cells in metaphase if I recall correctly. It is primarily used to treat gout, as it inhibits the movement and function of the white blood cells that cause all that pain & inflammation. In plants, it's supposed to arrest the cells in metaphase, when the (doubled) chromosomes are lined up. In the cases where conversion takes place, the colchicine is removed and the plant goes on to double all those chromosomes, which are already doubled, and now you end up with 2 complete sets before the cell divides.

The level required to induce polyploidy is very close to the lethal level (for the protocorm), which is why conversion rates aren't very good. In fact, some people like to advertise "colchicine-treated" for a nice cross when they use very little colchicine to get the maximum number of seedlings, and of course none of them has any chance of being polyploid.

[Heather]

Fascinating! However, I am not understanding why you say:
"of course none of them has any chance of being polyploid."


sorry, not too well versed in genetics...

[amaximia]

And of top of that PhytoTech tacks on a special handling fee cause the stuff is so nasty. Does anyone know a cheaper source for colchicine?

Heather, buy the 3rd or 4th edition of Rebecca Northern's "Home Orchid Growing" from www.addall.com. The 3rd edition costs $20 used. It is a well-worth investment and it explains all that, flasking, colchicine, poliploidy...

[Jmoney]

Fascinating! However, I am not understanding why you say:
"of course none of them has any chance of being polyploid."


sorry, not too well versed in genetics...

a good colchicine treatment will kill a percentage of the seeds, since the level required to induce polyploidy is close to the lethal level.

if someone has a nice cross (i.e. PEOY) and wanted to get the maximum number of seedlings, he could treat with a low level of colchicine that would not kill any seeds, but that would also have zero chance of inducing any polyploidy. the cross is still marketed as "colchicine-treated", however.

[Heather]

Thank you!

[Jmoney]

no problem.

[Nobody]

And of top of that PhytoTech tacks on a special handling fee cause the stuff is so nasty. Does anyone know a cheaper source for colchicine?

Heather, buy the 3rd or 4th edition of Rebecca Northern's "Home Orchid Growing" from www.addall.com. The 3rd edition costs $20 used. It is a well-worth investment and it explains all that, flasking, colchicine, poliploidy...

I am not sure if it is cheaper, but oryzalin is more or less safer. PhytoTech has this, too.

I don't mean to criticize Rebecca Northern's "Home Orchid Growing" because many people find it sacreligious. But some of the things like these subjects are not all that well explained. I do confess that I am relying on my memory since I don't own the book.

[SteveT]

Colchcine is one the most toxic substances known to man, and is typically a bad idea with orchids. Occaisonally you will get bigger thicker flowers because it doubles the chromosome number, often you get horrible mutations, especially in paphs.

[ATester]

yeah, and evidently, this stuff is derived from the roots of crocus plants...kind of makes me worried about how much and how often I use saffron (which is often in my cooking)