RE: HYB: Getting It Straight For the Simple Minded - RePost

Steve, you have asked some questions about which I believe a number of
others may also have a degree of curiosity.  I will make an attempt to
respond "for the Simple Minded."

There is a difficulty about reducing what is incredibly complex stuff to its
essential elements without making hash of what occurs in the conception and
birth of new plants from the sexual process.  Plants are not quite as simple
as animals, but the matter is actually pretty much the same except for a few
matters that make no difference as far as your question is concerned.

Normal "simple" plants and animals have two matched chromosomes in the
cell's nucleus for each chromosome in their basic set.  These are "diploid"
organisms, a word from Greek meaning simply "two-fold."

The pollen and the egg are "haploid," also Greek, meaning "half-fold."  Each
of those chromosomes is unique, and the "how many" is described as the
"x=number," even though one often sees the expression misstated as
"n=number."  I'll use "x" below.

Old diploid bearded irises from Europe, like *I. pallida* or *variegata* and
the hybrids between them have an "x" of twelve.  There are twelve unique,
different chromosomes in the set.

With bearded irises, around 1890 or so a few irises collected in Asia Minor
(modern Turkey) and other areas scattered from Greece to Afghanistan and
Kashmir on the border between Pakistan and India began to drift into
circulation in England and France, and later in the United States.  These
clones,
species, or whatever (some confusion reigns about these identities), several
of which are still available, were larger, heavier plants, bigger blooms,
but almost monotously blue-violet bitones in color .  AMAS is one of those
collected clones, and is listed by a number of major growers for its
historical interest.

Many crosses were attempted between these Asiatics and garden varieties of
bearded irises.  Very few of the crosses were successful, and when they
were, usually only had one or two seeds.

It turns out that many of these Asiatics have the same "x=12" of the
European irises, but have a total of forty-eight chromosomes, where the
older, colorful and hardy European varieties had only twenty-four.  They
were "tetraploid," again, the same Greek, but with "four" as the first part
of the word.

What happened to account for these one or two seeds is that something had
gone awry during development of the occasional ova (or more rarely, the
pollen grain) that was involved in these hybrid seedlings, and the result
was a "tetraploid" hybrid because *all* of the diploid parent's chromosomes,
two of each, had gone into the ovum or sperm (pollen grain), and when
fertilized with the Asiatic, produced colorful, beautiful, big hybrids that
were fertile.

All of our "tetraploid" TB's are descended mostly from these hybrids.

In a few cases, natural, wild tetraploids of *I. aphylla,* and *balkana*
have entered into the mix, and some other diploid species such as the dwarf
*suaveolens,* *reichenbachii,* (which also has a tetraploid form, I
believe), *imbricata* and others have been mixed in also.

You may notice that Jim and Vicki Craig in Oregon have a line of tetraploid
Miniature Tall Bearded irises (which are a classification normally diploid
in their chromosome makeup) that have been bred down in size by the use of
normal Tall Beardeds with *I. aphylla* in complex pedigrees.

None of this has depended on the chemical "boost" that colchicine has been
used to double the chromosome counts in JI's and Siberians.  Tetraploid LAs
also exist.

Your question about the arils and aril hybrids is a more complex one.  The
"x" of Regelia (Hexapogon) irises is eleven, and that of the Oncocyclus is
ten.

Several decades ago various people in California and elsewhere began trying
to get hybrids between these aril irises from the Middle East, from Israel
to Iran and Turkey and the bearded irises.

By an extraordinary streak of luck a hybrid occurred sometime before 1910
between the diploid Oncocyclus species *iberica* with twenty chromosomes and
the collected wild tetraploid Macrantha.  This produced a hybrid with all
twenty of the chromosomes from the Onco, and the normal half of twenty-four
from Macrantha.  Following a rule no longer allowed, the species name and
Macrantha were combined as IB-MAC, which has pollen that is quite fertile.
It has forty-four chromosomes, four "x" counts, two each of the ten from the
Oncocyclus set, and two sets of the twelve from Macrantha

When these chromosomes pair up to begin the process of pollen or ovum
formation, the ten Oncocyclus chromosomes pair with the other ten like
themselves, and the same thing happens with the twelve from the TB
Macrantha.

This behavior makes the plant behave as if it were a normal diploid with an
"x" of twenty-two.  However, that isn't what the hybrid is.  So a new term
comes in.  This is "Amphidiploid," again using the Greek.  There are other
amphidiploid hybrid varieties and a few species among other kinds in irises.

Modern ABs that are neither "+" nor "-" are only slightly more complicated
than this.  They often involve a mix of chromosomes from the Regelias, the
Oncocyclus and the various classifications of Beardeds.

That evolution has had the hands of many heroic, extraordinarily patient
people mixed in.

Your comment, "Arilbred iris are crosses with various bearded iris and aril
iris. For the most part, these crosses are fertile" opens a Pandora's Box.
The truth is, by far the largest majority of the early crosses produced
hybrids that were as sterile as they could be.  It was only by extraordinary
persistance, and according to one source I ran across years ago, helped
along through the throwing of IB-MAC into the mix, that the jump up to
"amphidiploid" fertile hybrids occured. This history makes great reading,
and I highly recommend it.

Curiously, there are other possibilities than "tetraploid," by the way.

If I remember rightly, edible modern potatoes are a product of some
extraordinary collecting and plant breeding by South American Natives that
involve at least five different wild species.  They are "Octoploid," meaning
"eight-fold" in their chromosome makeup.

Such things as "triploids" and "penta-" and "hexa-" hybrids of various kinds
also occur, including in irises.

In animals, on the other hand, any combination above diploid is usually
fatal.

Neil Mogensen  z 7  Reg 4  western NC mountains

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