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Tetraploid Arilbreds

RIck Tasco asked me to explain how to tell if a particular arilbred is a member
of the fertile family of balanced tetraploids.   If you're not interested in
hybridizing -- Ready, Aim, DELETE!

There's no simple, easy answer.  It's a matter of understanding the various
classification systems used over the years, learning to analyze pedigrees,
mastering the science of making test crosses -- and even learning to count
chromosomes if you're that ambitious.  

I can offer a few guidelines, though.  I'll be the first to admit that they
over-simplify things and for this reason could lead you to overlook some
significant, unusual breeders.  BUT it's a staightforward process of
elimination.  Each step serves as a screen and only the ones that pass through
that screen need to be checked further in subsequent steps.  The ones that do
make it all the way through this screening will definitely be members of this
fertile family -- good candidates for producing lots of seedlings.   (Notice to
lurking programmers:  this may be easier to understand if you flowchart it.)


If a variety was introduced before 1950, the odds are so much against it being a
balanced tetraploid that there's really no need to even look at the code.  There
are a handful of exceptions:  CAPITOLA (one-quarter I. iberica and one-quarter
I. gatesii), IB-MAC (one-half I. iberica), ISMALI (one-half I. iberica), LADY
LILFORD (one-half I. paradoxa), KOROLCYP (one-half korolkowii), JOPPA PARROT
(parentage unknown but counted as tetraploid), RIC-IB (one-half I. iberica) and
ZWANENBURG (one-half I. susiana) come to mind.  If you have one of these --
treasure it, use it.  (Lloyd, Mike, Larry, Clarence & any other historians out
there -- if you think of more examples, please chime in!)

If the variety in question was introduced between 1950 and 1976, you pretty much
have to rely on published chromosome counts and pedigrees.  The fully-fertile,
C.G. White-type tetraploid arilbreds are usually considered the foundation of
our modern, fertile family.  These include:  AHMED AGA, ARJUNA AGA, ASOKA OF
HIRFA, KALIFA KABUL, TATAI PASHA AND YUSSUF.  Arilbreds derived solely from
crosses among these varieties are also fully-fertile tetraploids.  For example,
TEL AVIV was produced by four generations of line-breeding IMAM AHMID, KALIFA
tetraploid.  There were compatible varieties introduced by other hybridizers, as
well, which were also counted as tetraploid -- varieties like ARDRUN, DON
RICARDO, and SHARKSIANA -- so they must be added to the list of progenitors. For
example, ESTHER, THE QUEEN  came from (ARDRUN x IB-MAC) X KALIFA GULNARE -- all
tetraploids -- so it, too, is tetraploid.  

If the variety was introduced between 1976 and 1990, the classification code
that appears in the decennial Checklist may provide some clues.   As originally
set up, the quantum system classified the fully-fertile, C.G. White-type
tetraploid arilbreds as OGBs.  In this period, an OGB was most likely (but not
always) tetraploid and other codes were most likely triploids or unbalanced
tetraploids.   But as the generations passed and pedigrees became more complex,
many fully fertile varieties had to be registered as OGB- or OGB+.  So the
classification code is not the complete answer.  It's necessary to go on to the
next step:  pedigree analysis.  

If a variety was introduced after 1990, however, the classification code itself
will provide a better clue.   By definition, OB, RB, and OGB all indicate
varieties that have an equal number of aril and nonaril chromosome sets.  You
can eliminate from further consideration any variety from this period that has
any other code (OB+, OB-, RB+, RB-, OGB+, OGB-).  The converse is not true,
however --  you can NOT assume that all OB, RB, or OGBs are fertile tetraploids.
Most chromosome-set OBs are diploids and most chromosome-set RBs are
tetraploids.  Chromosome-set OGBs are tetraploids, but the code alone does not
tell whether or not they are balanced -- you'll still have to look at the


An arilbred may come from a cross of an aril with a TB, an arilbred with a TB,
or an arilbred with an arilbred.  Start by determining which of these groups the
pedigree fits into.

Aril/TB crosses usually produce relatively infertile diploids or triploids, but
there are a few exceptions worth noting.  Watch for pedigrees in which one
parent was a tetraploid TB and the other was a tetraploid regelia -- the
arilbred they produced will be a balanced tetraploid.  This isn't as daunting as
it may seem.  I can't think of a single example of an arilbred registered since
1950 with a diploid TB parent (can someone else who likes a challenge???).  As
for the aril side, it's just a matter of watching for cultivars of the two
tetraploid regelia species:  I. hoogiana and I. stolonifera.  Henry Danielson's
GENETIC ARTIST and GENETIC LEADER are good examples.

Arilbred/TB crosses usually produce unbalanced tetraploids.  Once-in-a-while,
one of their offspring proves to be partially fertile -- but for the purpose of
these guidelines you should just eliminate these from consideration.  

Arilbred/Arilbred crosses can produce triploids, balanced tetraploids, and
unbalanced tetrapoids.  This can complicate the hybridizer's life -- but please
bear with me a bit longer.  If BOTH arilbred parents are known to be balanced
tetraploids, their offspring will also be balanced tetraploids and no further
testing is required.  But if one parent is a triploid and the other a balanced
tetraploid, their offspring can be either -- or if one parent is an unbalanced
tetraploid and the other a balanced tetrapoid, their offspring can be either.
In these cases, it's time to resort to test crosses.


These are the hybridizers'  tools for determining chromosome complements and
the proper code for a registration.  Test crosses are relatively easy.
Chromosome counts are much more complicated and definitely beyond the scope of
the current discussion.  Although they were very important in identifying the
first fertile tetraploids, they are now mostly reserved for iris with unexpected

For example, Gene Hunt's SUNRISE IN GLORY has a wide cross in its ancestry but
was the result of  attempts to breed toward fertility while injecting new aril
genes.  I registered it for Gene, and coded it as a quantum system OGB+ on the
basis of its pedigree.  It  is, however, a fully functional halfbred and if I
were to register it today I'd code it as a chromosome-set OGB.  There's no need
to count it.  Its pod parent is a quantum system OGB+ that was counted
tetraploid and its pollen parent was produced by line-breeding tetraploids so it
certainly  "should" be tetraploid itself and its breeding characteristics are
unquestionably those of a fully fertile tetraploid.  Its quantum-system
classification was just a quirk of the system.

In contrast, Les Peterson's BOLD SENTRY computes as a 5/16-bred and was
originally classified as a quantum system OGB-  (and it won the Wm. Mohr award
as such).   But because of it's extremely complex pedigree, half-bred-like
appearance and unexpected fertility, people started to suspect it was really a
functional halfbred.  When it was finally counted, it proved to be a balanced
tetraploid --  a chromosome-set OGB.   Such cases are extremely rare.  

For really complex pedigrees,  pedigree analysis can only tell you that a
variety MAY be a balanced tetraploid, not that it is.  That requires test
crosses and test crosses require a stock of KNOWN fully fertile tetraploid
arilbreds.   For example, by crossing the offspring of a triploid and a balanced
tetraploid back to another fully fertile tetraploid, it's possible to determine
whether or not it is also fertile.  When I'm testing a seedling, I make many
such crosses.  An occasional, scant pod is not proof -- many triploids show that
much fertility -- but if the variety being tested produces full pods with a
variety of partners and those seeds show good germination it can be judged fully

End of screening exercise.


1.	Proven Fertility.  If  you notice that a particular variety has LOTS of
registered children, grandchildren, etc. -- it's a pretty safe bet that it's a
fertile tetraploid.  Go ahead and use it.  

2.	If you have a question about a specific variety, just ask.  I'll post my
best guess, and reasoning behind it, to the list.

As I said in my earlier post, I like to work with wide crosses myself.  These
guidelines are just to help you identify the most promising breeding stock --
not to discourage anyone from exploring the possibilities.   The concept of
fertile families is a good starting point, a way to get lots of seedlings to
evaluate.  It's certainly not the whole story -- I happen to think the real fun
lies beyond work with just the fertile tetraploids, but not everyone wants to
make thousands of crosses in quest of a break in the fertilty barriers.  

Sharon McAllister

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