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Re: HYB: Daylength independent


Bloom period is a complex relationship between genetics and environment. The more I read the more complex it seems. There is a lot of current research on bloom triggers . There can be a switch from short night triggers to long day triggers under some genetic conditions. The number of factors that work together is amazing. Some sets plant up with potential to bloom, such as vernalization, but this requires a number of other things to be just right before bloom starts. And remember, in order to get bloom out of season we need defective gene controls. That is the genes that prevent bloom out of season are deflective in some way.

It appears that there are two sets of genes affected by vernalization. These two sets of genes are bloom prevention genes. Vernalization has the effect of turning these genes off so the plant is now set up to bloom when everything else is right. That is the plant is mature, has had flower bud differentiation, plant ha enough biomass, lighting and ambient temperature is right and the correct photoperiod has occurred. There is in some plants sensitivity to amount and type of light. For example, light reflected off other plants (in crowded conditions) has less red light as this is absorbed by chlorophyll. This can be a trigger or an inhibitor , depending on the specific plant species.

The two flowering inhibiting genes are Frigida (FRI) and Flowering Locus C (FLC). A natural defect in FRI will cause plants to bloom earlier in the season. A defect in FLC will result in plant not needing vernalization to bloom. That is vernalization gene works, but it is not needed. Another common defect seen is the presence of a modified vernalisation gene (VRN) called vrn2. In small letters as it is a recessive, Anything in capitals is a dominant gene. VRN permanently turns off FRI and FLC, and plant flowers. This change is permanent, that is plant is now primed to bloom and this effect can last for 300+ days. The only thing that can reverse this is very hot temperatures. The vrn2 gene only disables FLC as long as temperatures are cool.

So, on to speculation. A guess here, is that most rebloomers, that is cyclic rebloomers, are defective in FLC, so they don't need vernalization in order to bloom. So after bud is initiated, they can go ahead and bloom, even if it is fall. The summer rebloomers would be defective in FLC and FRI, Thus they would have extra early bloom. I think I read that plants that are defective in both FRI and FLC (I'll need to reread this information more closely to be sure) are now long daylight plants rather then short night plants, in regard to photoperiod trigger. This actually would be easy to test for. It would require putting something, like large garbage can, over the clump, for an hour in the middle of each day, every day, and compare it to a similar clump that is not covered in regards to rebloom.

I have read another account of early summer bloom in some plants, including Immortality, Queen Dorothy and Baby Blessed . Rebloomn starting in June and continuing to Fall. Plants were in an area where they got light all night from a security light. It makes me wonder about all those other reports of June/July rebloom. What were the lighting conditions?

The summary of this, is to get the rebloom characteristics of Immortality, Queen Dorothy etc, then you would need a full set of the recessive fri gene as well a full set of the flc (defective ones designated as lower case as it would appear that they are recessive) in order to get the strong early rebloom. Thus if one of these types is crossed to a plant that is a cyclic rebloomer you would need to sib or back cross to summer bloom plant to get the genes needed for summer bloom. This would also explain their response to extra light that is not there with other rebloomers. If crossing to a plant that is not a rebloomer, then you would get very low percentage of summer rebloomers in the F2, that is sibling cross.

Forever Blue would seem to have a defective photoperiod gene, and thus is daylight independent. Thus a cross of FB X Immortality (or other summer rebloomer ) would not have a full set of any reblooming genes as FB would likely have normal FRI and FLC genes. Again a guess here. Trying to find something that fits observations. FB also needs some other factor to explain its constant bloom, as photoperiod independent gene by itself is not sufficient.

This website <http://www.sci.fi/~benefon/sol.html> enables you to calculate daylight hours and also to get your locations latitude and longitude. There are several others that also will do this, just do a search for "photoperiod" to locate them

For my location spring bloom on Immortality, My 27th , daylight is 8:56. June 21st is 15.26, August 15th is 14.01 (time of rebloom on Immorality and Queen Dorothy.

Chuck Chapman

Date: Mon, 25 Feb 2008 07:50:31 -0500
From: Linda Mann <lmann@lock-net.com>
Subject: [iris] Re: HYB: Daylength independent

Aha!  Thanks Chuck.  I completely forgot about your summer nights being
shorter than ours.  We do occasionally get <June> rebloom of some of
these, but I <finally> get your point about trigger for dark exposure
being different where you are compared to here.

How many hours of darkness do you have on the summer solstice? Or the
time you estimate IMM is triggered to rebloom for you?

<Betty, Between spring bloom and July bloom appears to be close to 12
weeks. Enough time for a rhizome to mature.>

Somewhere, I have a calendar/table showing sunrise/sunset for the year
here for comparison.

<One more possibility is the  difference in daylight between here and
wher you are (Bettry, Linda and evryone else reporting July bloom)  I
get longer summer  daylight then you do. The farther north , the longer
summer days are. Thus shorter nights and we wouldn't get the night time
darkness necessary t otrigger bloom until later in year.>
- --
Linda Mann east Tennessee USA zone 7/8
East Tennessee Iris Society <http://www.DiscoverET.org/etis>
Region 7, Kentucky-Tennessee <http://www.aisregion7.org>
American Iris Society web site <http://www.irises.org>
talk archives: <http://www.hort.net/lists/iris-talk/>
photos archives: <http://www.hort.net/lists/iris-photos/>
online R&I <http://www.irisregister.com>

------------------------------

Date: Mon, 25 Feb 2008 08:58:25 -0500
From: autmirislvr@aol.com
Subject: Re: [iris] Re:HYB: Daylength independent

Chuck, this reminds me of another point.?

Some gardeners think that all summer bloom is just the result of Mother Nature being out of whack.?

It's been stated that ALL irises may have the rebloom capability?IF the right conditions (triggers) occur.? (I won't state who because I'm not 100% sure of authorship without research.)?

If this is the case, could ALL responses of rebloomers be the result of?the modifiers and triggers rather than genes?? This might more readily explain the effect of a security light or an off season?cool spell.?

I say it can't happen if the rebloom gene is not present!? If there is no gene that allows for off season bloom, surely there can BE no off season bloom!?Since the purpose is to block off season bloom for survival??

<<So it is hard to tell if it was a left over rhizome that had cone?through winter but didn't have biomass to bloom or new rhizome.?Another possibility is that it is very sensitive to the light from any? other source, such as the security light. This leads to the?speculation that some plants are more sensitive to this them others.?>>



- -----Original Message-----
From: irischapman@aim.com
To: iris@hort.net
Sent: Sun, 24 Feb 2008 11:27 am
Subject: [iris] Re:HYB: Daylength independent


A lot of factors to look at. The rapid increase is one thing I ws?
looking at with the cross of Forever Blue x Celebration song. there?
are a couple of seedlings that do have increadable incesase. IAt first?
bloom, that is the spring after seed germinated, FB had four flower?
stalks open. The ususal for SDB is one, occasionally two stalks at?
this time. After spring bloom finished I divided FB. there were 9?
plants?
?
About summer rebloom.?
?
Betty, Between spring bloom and July bloom appears to be close to 12?
weeks. Enough time for a rhizome to mature.?
So it is hard to tell if it was a left over rhizome that had cone?
through winter but didn't have biomass to bloom or new rhizome.?
Another possibility is that it is very sensitive to the light from any?
other source, such as the security light. This leads to the?
speculation that some plants are more sensitive to this them others.?
?
One more possibility is the difference in daylight between here and?
wher you are (Bettry, Linda and evryone else reporting July bloom) I?
get longer summer daylight then you do. The farther north , the longer?
summer days are. Thus shorter nights and we wouldn't get the night time?
darkness necessary t otrigger bloom until later in year.?
?
Chuck Chapman?
?
?o rebloom in some locations,?
but not GOLDEN APPLE.?
?
About 20 seedlings from this seedling X non-reblooming seedling from?
(IMM X CSONG) may be big enough to bloom this spring (after getting?
whacked by the freeze last spring). Very curious to see if any rebloom?
or produce secondary bloomstalks.?
- - --?
Linda Mann east Tennessee USA zone 7/8?
?
- - -----?
?
?
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