Re: HYB: Daylength independent

Date: Tue, 19 Feb 2008 20:07:06 -0500
From: "Mary Swann-Young" <MryL1@msn.com>
Subject: [iris] HYB: Daylength Independent

Chuck -

Do you have Again And Again?  How does it do up there?

Sure acts like daylength independent here.

Mary Lou, near Indianapolis, Z5

I have Again and Again, and it does rebloom for me. Sometimes two
periods of rebloom. But in late August.

What does it do for you that makes it exceptional?

For me, in my climate the bloom sequence is MDB  May 8th, SDB May 19th,
 IB May 26th, TB start June 2nd. Then rebloom sequence is  TB Aug 18th
(either immortality or Queen Dorothy)  followed by  IB rebloom about
Sep 10th. SDB  rebloom  starts about md October. Rebllom opposite
sequence from spring bloom. Most SDB rebloomers start only a very short
time before frost.  Of course the daylight independent plants, Forever
Blue, Blueberry Tart, Autumn Jester and Forever Violet  just keep on
going like the energizer bunny. Occasionally a few odd blooms from  a
couple of SDBs  but just one stalk and then gone. Precious Little Pink
(IB) will bloom  end of July or  early Aug  and sometimes later as
well. I understand that this sequence is not  the same everywhere.

I had been using the wrong term for the cold period that is required
for blom. It is called  Vernalization. Following is  the Wikepedia
entry for vernalization

""Vernalization (vernalisation - British English) is the acquisition of
the competence to flower in the spring by exposure to the prolonged
cold of winter. The word vernalization comes from the Latin word
bvernus,b meaning bof the spring.b

Many temperate plants have a vernalization requirement and must
experience a period of low winter temperature to initiate or accelerate
the flowering process, or, as the case with many fruit tree species, to
actually break dormancy, prior to flowering.

One of the most important influences that temperature has on the floral
transition is the vernalization response. Many plant species, including
winter cereals such as wheat through to Arabidopsis thaliana, must go
through a prolonged period of cold before flowering occurs. This
ensures that reproductive development and seed production occurs at the
optimum environmentally favorable time, normally following the passing
of winter.

Following vernalization, plants have acquired the competence to flower,
although they may require additional seasonal cues or weeks of growth
before they will actually flower.

In the much studied model species A. thaliana the apical meristem must
be vernalized in order to promote flowering. Vernalization of the
meristem appears to confer competence to respond to floral inductive
signals on the meristem. A vernalized meristem retains competence for
as long as 300 days in the absence of an inductive signal. It is
possible to de-vernalize a plant by exposure to high temperatures
subsequent to vernalization.

Some plant species do not flower without vernalization. Many biennial
species have a vernalization period, which can vary in period and
temperature. Typical vernalization temperatures are between 5 and 10
degrees Celsius (40 and 50 degrees Fahrenheit). ""

I had been doing some research and found a few interesting facts. The
Flower Bud initiation in iris  typically sets the end of  August  in
Japan (Where the research was done)  with daylight temperature  was
average 26C. Thus probably earlier  in cooler climates.  This involves
the Meristem tissue (growing point of stem) changing  from producing
leaves to producing a flower stalk. In addition iris ( we are talking
oncers here) need the  winter vernalization to set bloom. That is the
days with cooler weather , but not freezing as plant needs some
biological activity). Then  it needs  the correct length of daylight to
trigger bloom.  (actually it is correct amount of night time.) Then it
needs correct amount of biomass, usually  involving rhizome size and
number of leaves.
The commonest example of daylight Neutral flowering given is Dandelions
, they bloom whenever a plant reaches maturity.

 Immortality  can sit in my garden with mature  size rhizomes and lots
of  leaves, but doesn't bloom until Mid to late August. This would
suggest that it is not daylight independent.
Forever Blue does bloom whenever a rhizome reaches maturity.

Chuck Chapman





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