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Re: hosta-open DIGEST V1 #14

  • Subject: Re: hosta-open DIGEST V1 #14
  • From: halinar@open.org
  • Date: Fri, 31 Oct 2003 00:06:49 -0800

Bill:

>Ben suggests (correct me if I'm wrong) that TC batches that grow 
>extremely slowly could be the result of poor hormone balances 
>impacting the health of the plant in a way that interferes with their 
>normal processes and therefore growth like a malnourished puppy.

This could happen over a short period of time, but it won't last for 
years.  If you spray some shrubs with 2,4-D, but not enough to kill 
it, the plant can maintain a deformed look for several years.  
However, the hormone levels in TC are actually quite low, so it's not 
likely that hormone levels will have any long term inpact.

>Some of the TC 'Great Expectations' are a good example. Even after 
>3-5 years (assuming the plant survives), growth never seems to return 
>to "normal".

I've picked up these poor growing variants from non-TC propagation, 
but there are also some variants that aren't quite as bad as the one 
you describe.  Whirlwind is another one where you can pick up some 
weird variants, but also some nice ones.  I have a bunch of off type 
Whirlwinds that I am watching and if I can get them to bloom I might 
be able to make some comparative crosses as I have a ventricosa 
Aureomarginata seedling that sets pods with Whirlwind.

>To me, this suggests a mutation has occurred.

Extreme variants like the poor growing variant of GE could also be due 
to chromosome damage.  Many of the variants we see in hostas show up 
in basically the same form in different gardens over time, which would 
not suggest random mutations.  My hypothesis for this is that hostas 
have a high level of transposable element activity and that these 
transposable elements have preferred locations of varying degrees of 
stability.  

>What I'm thinking here with this is that there are some types of
>mutations that are more likely to occur with exposure to auxins and
>cytokinins in the TC process.

My view is that the auxins don't cause the variants because it really 
isn't all that difficult to pick up these variations in non-TC 
propagation if you induce old buds to grow.  What the auxins do in TC 
is force the meristem buds to form and mature faster then regular 
growing conditions.  What is then happening is that the transposable 
elements are moving about and if a "mutated" bud becomes the dominant 
bud in a TC batch, then all the resulting regenerated plants will have 
that "mutation."  Thus, it's easily possible to get whole batches of 
TC plants that are poor growing because the poor growing doesn't show 
up until you take the plants out of TC and put them into soil.

>but my point is that there seem to be mutations that are common in 
>tissue culture but rare in natural division.

So far I haven't seen any common TC variant that hasn't also showed up 
in non-TC propagation for the limited number of hostas I've used in my 
experiments.  The secret is to induce very old buds down in the crown 
to form new plants.  If you are doing some very aggressive Rothsizing 
or crown divisions you can induce some of these old buds.  

Joe Halinar

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