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Abgeschickt von Uta von Rad am 25 September, 2003 um 10:43:08
Antwort auf: A simple bleaching model von Bill Steele am 20 September, 2003 um 07:06:14:
I like Bills model a lot and I want to add a piece that is related to parts of it: I agree that - especially with some Cypripedium species a longer bleaching time is beneficial. But there is - like Bill says - always the danger of over-bleaching. Of course there is always the problem of seed quality. Very often germination rate depends on how good the seed is. Sometimes embryos are small or they have been squashed in the mail or other things aren´t optimal. But in general there are species that germinate easier (for example Cyp. reginae) and others are more difficult. What I want to share with you are my results in trying to circumvent the problem of too long bleaching.
Bill writes: "The detailed nature of the mechanism by which bleaching enhances germination remains unknown, and the action of the bleach has been variously hypothesized to result from: 1) physical destruction of the carapace covering the embryo, 2) dissolution of germination inhibiting compounds within the embryo, 3) oxidation of such compounds, or 4) chemical action resulting from the high pH of the bleach."
Now I am trying to find a solution to point 4. My thoughts were that it is possible to soak the seed for some time in a solution of high pH that isn´t as toxic as bleach solution and thus leach high pH germination inhibitors (like for example Abscicic acid) out of the embryo BEFORE actually starting to bleach. I got some ideas from Camiel deJong and from Bill Steele and finally decided to try a solution of water with a drop of detergent that I adjusted to pH 12.3 with Potassium Hydroxide (KOH). I use KOH also to adjust the pH of my growth media and it is not very toxic. I soaked seeds from different species in this solution for 5 hours and after the treatment bleached normally (bleaching is shorter after KOH treatment as the pH is already high). My trials are just a few and it might not help with every species but I had some good results and will keep on trying. My germination results are in general:
flavum: as good as without KOH-treatment
tibeticum: slightly better with KOH-treatment
parviflorum: as good as without
macranthos: slightly better
xventricosum: slightly better
kentuckiense: with the seed I had I did not get any germination without KOH but about 10% germination with KOH
To test if KOH was toxic I put half a batch of parviflorum seed in the KOH-solution and left it in the refrigerator for a month (!) then I sowed it together with the second half that was not subjected to KOH-treatment. The germination was equal for both batches. So there does not seem to be any toxic efect (at least not for parviflorum...)
My general impression was that KOH-treatment helped more with seed that is a bit older (helped me germinate some acaule from 1999). Also its influence is different from species to species. Some (like flavum or parviflorum) do not seem to need it but it seems to help others. So I would summarize that KOH-treatment does not necessarily help but it probably doesn´t hurt and it might help in some cases. I will continue my experiments with this.
None of my experiments are really representative (I do not have the capacities or time to sow large numbers) but maybe this is interesting to some of you. I am of course very interested in your thoughts about this!
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