Re: heterosis and the "rebloom gene"

In a message dated 97-03-18 15:48:41 EST, Tom Tadfor Little wrote:

<< Clarence's hypothesis is that crossing irises from widely different lines
 of breeding yields seedlings with hybrid vigor, which in turn produces
 rebloom.
 
 I agree, but I'd like to suggest that rebloom DOES have a genetic component
 as well.  >>

Tom, I do not at all disgree with your statement quoted above. Although I
didn't state this in my most recent article, in the 1st article "The Origins
of Remontancy" I said this: "For years I was amazed that Rundlett
concluded...that remontancy is not caused by genetic factors but rather by
'special climatic influences.'  Climate is an important factor influencing
rebloom; but to deny the probablity of genetic causes on this basis seemed to
me to be an extreme conclusion.  Based on the facts at hand I would not rule
out a genetic origin for remontancy.  However, as Rundlett undoubtedly
believed, there may be no specific gene for remontancy."

Based on available facts, I see no reason to revise my thinking on this at
present.  I am not a scientist and certainly not an expert in biology or
genetics, but I enjoy studying these subjects.  I am an ardent believer in
the scientific method, and in keeping an open mind,  and will rapidly change
my views if a better set of facts are presented.  Being somewhat of a
biological determinist, I would find it difficult to comprehend if there were
not a genetic basis for rebloom, but it is most likely not a simple
dominant/recessive gene type of cause and effect.  After all, heterosis
itself has a genetic basis as I understand it. 

Tom continues: <An iris needs two things to be a reliable rebloomer:

(1) A defective biological clock(s). Most irises *know* when they're
supposed to bloom, and that is once a year, in the spring. (Look at the
consistency with which some bloom early and others late.) This timer must
be at least partly disabled in rebloomers. Perhaps different defects
account for different patterns of rebloom (everblooming, fall blooming,
sporadic blooming). I suspect this is genetic, and probably recessive in
most cases--or at least requires more than one dose for manifestation at
the tetraploid level.>>

Comment:  This is an interesting theory, but in terms of accepting it I must
remain at present an agnostic.  I can see how an extremely vigorous hybrid
could be  triggered to bloom "out-of'-season".  But my inclination is to
emphasis the "trigger" rather than the "disabling of the timer."  I
 acknowledge, however, that on this my "inclination" is based on logical
speculation---and I know enough about science to know that logical
speculation is often wrong.  Still, at present, I find "triggering because of
heterosis" theory the most logical explanation.  I would love to be proved
wrong, because I really would like to know "the truth."    

Tom also makes this comment: <<We can also all probably think of irises that
have extraordinary vigor
(more than some reliable rebloomers), requiring frequent division, and yet
never rebloom. (I know a lot of arilbreds that grow this way.) Something
besides vigor is clearly required and missing in these irises.>>

Comment:  This is one of the best pieces of evidence for the "defective
timer" theory. But I would point out that one cannot really tell with the eye
whether once-only blooming irises with "exceptional vigor"  really have
greater heterosis than dependable rebloomers.  One example of the type of
vigorous once-only blooming iris is INSTRUCTOR.  It behaves like a rebloomer
in every respect save one---it doesn't rebloom.  (It is always one of the
first TBs to bloom, and increases like mad---like mad!)  

There is no question in my mind that rebloom is climate and weather
dependent.  An iris like CHIEF HEMATITE is a very vigorous iris, and in
warmer, drier climes is apt to rebloom.  It is quite vigorous for me in
northern VA, but never reblooms in my wet, cold climate locale.  Although
very vigorous, in my climate is apt to rot when the rains begin.  It is heavy
genetically in I. mesopotamica.  It certainly demonstrates heterosis, but its
"trigger" is hotter weather than my autumn affords.  (Or in terms of the
"defective timer gene", its timer doesn't get "turned off" by my
climate---but I have problems typing this because I don't believe it at
present.) 

A personal "Thank you" for the nice comments on my article, Tom!  I find this
subject fascinating and important, and thus can run on and on---and to  those
whom I have bored with this rather lengthy message,  please excuse my
rambling.  Cheers to all, Clarence Mahan in VA
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