HYB:Source of Tangerine Factor

Tom, in response to your question about the origin of "t" you are quite right
about TWOI.  The information there does not reveal the source.

Keith Keppel, I believe, has offered the informed opinion that it comes from
*Iris kashmiriana* presumably via the Dominant Whites KASHMIR WHITE (1912) and
MISS WILLMOTT (1910).  MISS WILLMOTT is identified in the 1939 *Check List* as
a seedling of *kashmiriana*.  No parentage is given for KASHMIR WHITE, but it
is an easy and natural step to conclude it also came from that source.

I've never asked Keith if he is responsible for that opinion.  I should do so,
as I wouldn't care to ascribe to him what isn't his--especially if it should
be found to be wrong.

The scattered appearance here and there of the original "t" appearances is
easy to account for if the speculated origin is correct.

Recent research shows the synthesis pathways of the carotenoid pigments to
have Lycopene, the oil-soluble pink pigment in iris, before, not subsequent
to, the principal yellow pigments.  With the presence of 4-plex "t" the
conversion of Lycopene is stopped and and at least some of the carotenoids
remain orange-red instead of being converted to yellow.

The gene "t" is thus a blocker, not a converter.  I suspect that it is a
slightly different form of the enzyme that would take Lycopene to its next
steps--alpha- and beta-carotene.  One enzyme acting alone is responsible for
the beta- conversion, which suggests "t" is either another catalyst or enzyme
preventing the conversion enzyme from acting, or, more likely, a variant form
of the beta- conversion enzyme itself.  Alpha-Carotene requires the action of
the same enzyme, plus another, so it, too, is prevented from being formed.

Yellow would result if even one of the four possible genes for the normal
enzyme converting Lycopene to beta-carotene is present--"Tttt" in shorthand
form.

Chuck Chapman has suggested that at least some conversion is blocked if the
genetic makeup is Tttt.  I think that is true, too, as, like Chuck, I think I
see a difference in the quality of the yellow in Tttt flowers.  The beards
also show a warmer, richer color deep in the throat of such varieties.  Both
Chuck's and my opinions in this matter haven't been subjected to chemical
tests, however, to the best of my knowledge.

So, short and simple:  The probable origin is the clone of *kashmiriana* in
Sir Michael Foster's garden in the first decade of last century,  and the
recessive gene acts by preventing the conversion of Lycopene to yellow forms
of the carotenes--more or less.

I do not believe the clones of *kashmiriana* now available are the white form
in Foster's garden from which MISS WILLMOTT and probably KASHMIR WHITE are
derived.

What is said above leaves the question open as to how yellows with tangerine
beards can occur.  Gamma-Carotene?

The genetics of bearded irises, especially the tetraploids is bewilderingly
complex.  It seems almost anything can happen.

As an example the interrelationships of the various plicata alleles with the
broken color and zonal patterns, both of which appear to be closely associated
with the pl genetic series, has not been explained, at least as far as I know.
I'm interested in knowing how these patterns work.
.
Neil Mogensen  z 7 western NC mountains

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