Re: HYB: Removing germ. inhibs. pt 2
<Caution against any mustard compounds.>
Fortunately, BAM is British <anti> Lewisite. It was developed as a
treatment for mustard agent exposure, so isn't a mustard agent itself.
<I'd be interested in the Sulfuric acid data>
To back up a little - bearded iris seeds have two (at least?) types of
germination inhibitors. One is in the seed coat, the other is
Soaking in aerated or frequently changed water or removing the seedcoat
removes the inhibitors in the seed coat, but chilling is required to
remove/break embryo dormancy (also known as physiological dormancy, I
think I read..)
Lots of different things have been used to speed up removing seed coat
dormancy, including various mechanical (scarification) and
thermal/chemical methods, including sulfuric acid soak to remove part of
the seed coat.
Removing the seed coat or removing the inhibitors in the seed coat
doesn't affect embryo dormancy, which is most easily removed by chilling
in moist, aerobic conditions (i.e., damp but not soggy paper towel
burrito rolls in the fridge for 3 months).
=====According to some information I read yesterday, there is something
called heat-induced thermodormancy (defined a little differently in
different sources I looked at) in which seed ripening at high
temperatures or exposed to high temperatures can enter deeper embryo
dormancy that requires longer chilling than they would otherwise. High
temperatures cited were 30 to 40oC (where's my calculator - I think
that's in the 90s?).=====
The following are treatments that are known to shorten the duration of
or eliminate <embryo dormancy> (i.e., eliminate need for chilling) in
various plant species. Sometimes, these treatments apparently improve
uniformity of germination. Some of these are discussed in Vallette's
book & I will post details later.
1) Gibberellin - Gibberellic acid (GA) promotes germination in many
seeds. Seed may be soaked with concentration of 100 to 1,000 ppm for
24 hours. I think I've seen some kind of GA (rooting hormone?) for sale
More details from another website (lecture notes, I think..): soak seeds
overnight in100-500 ppm GA3 (better if buffered), K-salt formulation,
which has excellent solubility. Pro-Gib is a commercial product that is
sometimes used. GA can cause seedling elongation in some species.
2) Cytokinins - Natural growth hormones stimulate the germination of
many kinds of seed by acting at the molecular level on biological
processes. According to what I found on the web, "synthetic cytokinins
are available from tissue culture supply houses, but since they must be
kept at a low temperature to prevent
decomposition, they are not available in garden supply centers. Soaking
for three minutes in kinetin at concentration of 100 ppm has been
recommended. Another website recommended soaking seeds in 100 mg/l (100
ppm) Cytokinins ( Kinetin, BAP, Zeatin). (This has been shown to
overcome high-temperature dormancy in lettuce seeds, for what that's
3) Ethylene - This gas occurs naturally in plants and has a number
effects, including the stimulation of seed germination. According to one
website, one of the chemicals available to gardener to generate ethylene
is Ethephon & another website mentioned Ethrel. Ripening fruits also
generate ethylene, but I don't know what concentrations are supposed to
be helpful in germinating seeds.
=====The same web site said that since gibberellins, cytokinins and
ethylene are the three dominant components in initiating germination,
they work best when applied together.
4) Potassium Nitrate - Many freshly harvested dormant seeds supposedly
germinate better if soaked in a 0.2% potassium nitrate solution.
Somebody asked before what concentration of nitrate was recommended, &
for how long, but I couldn't find any details before - here it is!
Seeds should be soaked for no more than 24 hours and then rinsed well.
Those are the generalities - on to details, starting with sulfuric acid,
since you asked.
Linda Mann east Tennessee USA zone 7/8
East Tennessee Iris Society <http://www.korrnet.org/etis>
American Iris Society web site <http://www.irises.org>
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