Re: REB: genetics, origins
iris@hort.net
  • Subject: Re: REB: genetics, origins
  • From: C* C* <i*@aim.com>
  • Date: Fri, 3 Feb 2012 18:08:44 -0500 (EST)
There are no rebloom genes per se. All the genes involved in timing of blooms are there to maximize plant energy, so control blooming as to when plant is most available to support bloom (plant maturity) and conditions are appropriate (eg; spring, vernalization genes) and to enable timing so insects/birds are available to pollinate, and to ensure there is time for seeds to develop (so bloom time is spring). Also genes to prevent bloom in fall when no time to mature seed, thus need for winter dormancy (vernalization and or short day dormancy genes)
There are no daylight photo-period control genes for most iris. Most iris are day-neutral. The bulb iris, English and Spanish iris are exceptions , as they have photo-period controls. Most iris species have vernalization genes, requiring a cold period before plant is released to bloom. There are variation in vernalization genes.
Some species HAVE to have vernalization before they can bloom. This is called "Obligatory" vernalization. Lets call this gene vo. Some plants from Mediterranean climates have vernalization genes (an allele on vernalization gene site) that can sense time since "bud set" and after about five months will initiate spring growth as if plant had a winter but wasn't cold enough for proper vernalization. It then assumes that after five months, winter must have come and gone, and proceeds to initiate bloom. This is called "facilitative " vernalization. Lets call this gene Vf . A plant with one copy of this vernalization reblooms in warm climates such as California, but not in other climates.
Some species, specifically alphylla, don't have a vernalization gene. They have a short day triggered winter dormancy gene, involving dropping of leaves. You can see them go dormant and leaves dry up in fall. You can consider them to have a null vernalization gene, or inactive gene in that location.
When we mix the winter dormancy genes ( aphaylla null vernalization , call it Va) with regular vernalization gene (then there is no requirement for vernalization. And in many cases the photo-period dormancy gene is inactive, as it would appear to be a recessive gene. Thus the plant does not need vernalization. This gives the fall cyclic rebloom as it doesnbt need vernalization, and winter dormancy genes are not in a recessive set.
So cascading dominance of vernalization alleles is Va > Vf > vo. If plant has an Va gene, it has fall cyclic trigger. If it has a Vf , then it is a warm climate (ie California) rebloomer. If it has only vo, then it needs vernalization before it can bloom.
The summer rebloomers turn out to initiate bloom as soon as they have bud set ( maturity, plus temperature signal). This is a result of some sort of defective gene, or more likely two defective gene. Both have to be in four copies in order to have the summer rebloom.
I. suaveolens var. mellita may very well be a photo-period triggered dormant plant, like aphylla.
Once a plant has the potential to rebloom, then all of the secondary factors come into play. These involve plant growth rate, maturity level, as measured by mature leaf count, and ability to utilize energy from itbs environment. These all seem to be multi-factor genetic situations. That is several genes are involved in each of them, with a cumulative effect. But wilh all these factors, there wonbt be rebloom unless the genes controlling bloom triggers are in place. 

Chuck Chapman


-----Original Message-----
From: Linda Mann <lmann@lock-net.com>
To: iris <iris@hort.net>
Sent: Fri, Feb 3, 2012 8:36 am
Subject: [iris] REB: genetics, origins


I think there have been discussions here in the past about the
probable/possible origins of rebloom in TBs, but I've forgotten and was
wondering if there is an article somewhere that details their history?
Maybe in the Reblooming Iris Society Recorder, or one of the other
AIS/affiliate pubs?

I haven't looked yet, & am not really sure how to narrow down a search
of the archives for the info.
Especially wondering about theories of where the rebloom genes came from 
that Smith and G.P. Brown were working with?  Esp. the heat tolerant
'summer' blooming 'cold climate' rebloomers.

Tom Silver's reblooming CRICKET SONG, from I. cengialtii , I. variegata
(Beardsley clone),& I. suaveolens var. mellita, has gotten me wondering
about it again.  Wondering if these rebloom genes are the same as those
in IMM, VIOLET MIRACLE, or another suite.

Linda Mann east TN USA zone 7b

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