Seed sowing media - why potassium iodide ?

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myxodex

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I'm setting up to have another go at orchid seed sowing, this time with a Neofinetia cross. I've heard that they can be a bit tricky. I've ordered a medium recommended for Vandas and related genera called SBL-A, but I thought I'd experiment with a few home made recipes just for a bit of fun. Searching through the literature of seed sowing media I noticed that a few of the traditional ones have KI added ... but why? Roth's recipes don't call for KI so it seems it is not essential.

I can't find a lot (available to me that is) on Neo germination, except a Korean paper with an abstract in english; they use apple juice and optimal pH was 4.6 !
 
Good luck Myodex

Some one probably thought it was a good source of K and threw it into the brew:poke:

I don't know if you saw that article in Orchids a few years back about germinating/growing out orchids in mychorizae inoculated gelatin pills with nothing but peat moss for the food substrate.

I don't think it even required sterilization and aseptic technique.

So going downhill from there, I don't think the total nutrient base needs to be more than what you can get out of peat moss. (which doesn't have a lot of potassium iodide in it).
 
When you look at media formulations, you can't assume that every component is there because it has been optimized for a purpose. It could be there because it was convenient, and didn't interfere with the immediate objective. Just speculation, but it is possible that KI was used primarily as a K source that someone happened to have available, perhaps in purer form than the KCl they had available, or perhaps chosen in part because it didn't add some other nutrient of interest. Once someone published a formulation with KI others may have adopted it simply as experimental protocol - change this or that while holding everything else constant. Iodine probably is essential, KI is fairly cheap and available, so as long as it doesn't provide a toxic level, why not?

Medium that doesn't contain iodine specifically may still supply it as an almost inevitable trace in all but the most highly purified chloride compounds or from organic additives.
 
Thanks for the replies. I just thought that I was missing something that should have been obvious.

Kirk, I know what you're saying about methodology in science, sometimes it takes years for some quirky detail of a protocol to emerge as unecessary when some grad student forgets to do it, or include it, and the method still works perfectly !

I finally did some googling and found this google book reference which has a section on this. The one idea is that KI might act as a reducing agent in plant tissue culture, but not all results are consistent with this.

http://books.google.co.uk/books?id=...v=onepage&q=iodide toxicity in plants&f=false

Tyrone, thanks for the reference, it sort of agrees with what I found here;
http://aob.oxfordjournals.org/content/34/4/919.abstract
which is that low concentrations (< 5 ppm) can be stimulatory for some species but generally inhibitory or even toxic above 10 ppm.
Also the organic additives are bound to generate some iodine from the iodide.

I'll follow idea in the Seaton and Ramsey book and try some maxicrop, it will certainly provide some iodide/iodine along with auxin and just about half of the rest of the periodic table !
 
Any sea-derived product would have I in it - agar and seaweed extract would have plenty.
 
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