RE: The Tetraploid file

Neil,

Thanks for your most excellent answers. 

Actually, the post that showed up earlier this morning was the original one
I had sent and seemed to disappear, and the original one you answered was a
repost. Perhaps the original e-mail was traveling the world in search of
answers? 

\\Steve// 

-----Original Message-----
From: owner-iris@hort.net [o*@hort.net] On Behalf Of Neil A
Mogensen
Sent: Saturday, May 14, 2005 8:04 AM
To: Iris-talk; Steve Szabo
Subject: [iris] The Tetraploid file

Dear Steve,

I see the repeat of your post, and it reminded me that you might be
interested
in the cleaned up file.  Here is a copy in response to several requests I
had
for a "keeper" quality file of what I responded.

Diploids and Tetraploids

I was asked some questions on Iris-talk about a subject which I believe a
number of people may have a degree of curiosity. I will make an attempt to
respond, as asked, "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
details that make no difference as far as the question is concerned.

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

The pollen and the ovum (egg) are "haploid," also Greek, meaning
"single-fold." Each of those chromosomes in the basic set is unique. 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, each iris plant having two of each kind.

With bearded irises, around 1890 or so, a few irises collected in Asia Minor
(modern Turkey) and other areas scattered from Greece to Israel, and from
Iran
and Afghanistan to Kashmir began to drift into circulation in England and
France, and later into 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
monotonously
blue-violet bitones in color .

AMAS is one of those collected clones. It 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 the pods held only had one or two seeds.

A number of remarkable advances in quality came from such crosses.
ARGENTINA,
one of the Mohr-Mitchell seedlings from California, was from (Catarina X
mesopotamica). CONQUISTADOR, one of the varieties from Mohr before his
death,
was from (Juniata X mesopotamica). Bliss, in England, introduced DOMINION in
1917. Its parentage is (Cordelia X Macrantha). All of these crosses were
from
the pollen of the collected tetraploids used on the familiar diploids
Catarina, Juniata and Cordelia. These are just three of the relatively few
tetraploid hybrids forming the foundation of our larger modern bearded
irises.

It turns out that these Asiatics have the same "x=12" of the European
irises,
but many of them have a total of forty-eight chromosomes, where the older,
colorful and hardy European varieties had only twenty-four. The majority of
the new Asiatics 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 was 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 from these hybrids.

In a few cases, natural, wild tetraploids of I. aphylla and balkana have
entered into the modern mix. Some other diploid species such as the dwarf
suaveolens, reichenbachii, (which also has a tetraploid form, I believe),
imbricata and others are found in the ancestries of our modern hybrids.

Jim and Vicki Craig in Oregon have a line of tetraploid Miniature Tall
Bearded
irises. MTBs are in a classification normally diploid in chromosome makeup.
The Craigs have bred TBs down in size by the use of I. aphylla in crosses
with
them, and combining the seedlings in complex pedigrees.

None of this development of tetraploids from the ancestral diploid condition
has depended on the chemical boost that colchicine provided to double the
chromosome counts in JI's and Siberians. Tetraploid LA varieties induced by
chemical agents also exist.

The 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 semi-desert Middle East,
Israel, 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 numbering twenty-four
from
Macrantha.

Following a rule no longer allowed, the onco species name and Macrantha were
combined as IB-MAC, which has pollen that is quite fertile. It has
forty-four
chromosomes. There are 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.

To describe this behavior, a new term comes in. This is "Amphidiploid,"
again
using the Greek. There are other amphidiploid hybrid types and varieties and
a
few collected species of iris have been found to be natural amphidiploid
hybrids of other iris species. I. pumila is an example of this. It is an
amphidiploid hybrid between I. attica and I. pseudopumila. There are other
examples of the phenomenon found among irises.

Modern ABs that are neither "+" nor "-" are only slightly more complicated
than amphidiploids. They often involve a mix of chromosomes from the
Regelias,
the Oncocyclus making up the aril half of their genetic mix, with the other
half coming from various classifications of the more familiar bearded
irises.


This revolutionary development has had the hands of many heroic,
extraordinarily patient people mixed in. The comment included with the
questions, "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 were between
diploid aril species and diploid bearded irises, producing hybrids that were
as sterile as they could be. The variety WILLIAM MOHR has many descendants,
all of which are the result of unreduced gametes, that condition which
results
in an ovum (in this case) with all the parent's chromosomes included
fertilized by the other, tetraploid, parent. Few others of the diploid
hybrids
have any progeny.

It was only by extraordinary persistance, and according to one source I ran
across years ago, probably helped along through the use of IB-MAC in 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." If I remember
rightly, edible modern potatoes are a product of some extraordinary
collecting
and plant breeding by native South Americans that involve at least five
different wild species of Solanum. Modern potatoes are "Octoploid," meaning
"eight-fold," in their chromosome makeup. Such things as "triploids" and
"penta-" and "hexa-" hybrids of various kinds also occur, including a few
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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