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Re: Hosta Seed Maturation

  • Subject: Re: Hosta Seed Maturation
  • From: "W. George Schmid" <hostahill@Bellsouth.net>
  • Date: Thu, 19 Aug 2004 13:37:03 -0400

John, Bill, All,
Your observation is astute. I have noticed the same. My theory is that
abscisic acid is at work. It is the plant hormone that causes growth to slow
down and go to a dormant state during winter (or too hot summers) by
suspending primary and secondary growth. The most impressive effect of
abscisic acid is in the inhibition of growth and the maintenance done on the
dormancy of buds. AA develops as the temps go down in autumn and after
reaching a certain level, dehiscence (splitting open) of seed capsules
follows, releasing the now ripe seeds. The
timing of this event coincides with lower night time temps, rather than
freezing temps. In the North, where the hostas come up much more "together"
the low temps in early fall come as most of them have reached sufficient
length of development time to get triggered into dehiscence together. In the
South, it is sometimes the hot summer temperatures that trigger development
of AA, which is also a plant stress hormone. Under these circumstances (too
hot) AA also develops and triggers heat dormancy and the pods will also
dehisce no matter whether the seeds are ripe or not. By the way AA also
makes the leaves fall off the trees in fall. Auxin, cytokinins, and
gibberellins oppose the effect of AA by stimulating growth in the tissues.
AA is also a growth (germination) inhibitor for bud and seeds preventing
germination during unsuitable outdoor temps. In Spring photoperiod and other
stimulates trigger the degradation of abscisic acid and auxin, cytokinins,
and gibberellins initiate the growth of dormant buds and germination. Since
the actions of AA are triggered by cold or too hot temps, the timing of
events depends entirely on the local climate. If you bring a hosta in to
prevent the seed pods from being frozen, the only way to make it dehisce is
to dry it out. High temps inside will not trigger AA but stressing the plant
by withholding water will. The problem is that you can trigger dehiscence
but it may be on a pod that contains seed that is underdeveloped (not ripe).
This is NOT the natural process. Under normal conditions, the seeds always
have enough time to ripen but the pods will not dehisce until dormancy nears
(i.e., enough AA has developed) and the normal temperature range allows the
seeds to be dispersed and covered. All of this can be upset by drought, very
early freezes, way too hot summers with attending lack of rain and other
unusual climatic conditions. Nature knows what it is doing, my friends, well
most of the time anyway.

HTH George

W. George Schmid
Hosta Hill - Tucker Georgia USA
Zone 7a - 1188 feet AMSL
84-12'-30" West_33-51' North
Outgoing e-mail virus checked by NAV

----- Original Message -----
From: <Jaspersail@aol.com>
To: <hosta-open@hort.net>
Sent: Thursday, August 19, 2004 11:42 AM
Subject: Re: Hosta Seed Maturation

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