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HYB: William Mohr Giant--an amphidiploid?

  • Subject: [iris-photos] HYB: William Mohr Giant--an amphidiploid?
  • From: "Neil A Mogensen" neilm@charter.net
  • Date: Wed, 3 Dec 2003 16:14:35 -0500

Robt R Pries suggests William Mohr Giant may have arisen from a faulty mitosis where the two sets of chromosomes (10 from *gatesii*, 12 from Parisiana) did not separate and a doubling occured.
This is not exactly what does occur in the colchicine and Oryzalin (Surflan) treatments, methods for which are published for use with tiny seedlings.  The doubling occurs due to a disturbance during meiosis, not mitosis.
There are natural tetraploid and amphidiploid hybrids that exist in irises.  The Asiatic tetraploids, such as *trojana*, *mesopotamica*, Amas and Ricardii among the TB's and *Iris pumila* among the dwarf bearded are examples.  We do not know *how* these arose, but in the case of *pumila* the parentage is apparent from the karyotype (an anysis of the morphology of the chromosomes), which reveals the ancestry to be hybridization from *attica* and *pseudopumila.*  The only karyotype I have seen published of an Asiatic tet is that of *kashmiriana*, and it resembles *Iris pallida,* even though the phenotype does not.
I do not believe polyploidization has ever been noted in garden irises except through seed--such as those like DOMINION which were from pods containing one or two seeds and involved the Asiatics on one side of their ancestry and diploid European beardeds on the other.  The great majority of these involve seeds forming on the diploid as podparent.  The reverse, the diploid registered as pollen parent, are rare but include SNOW FLURRY for one.
Since animal pedigrees put the male parent first and the female second, some early breeders may have followed that pattern.  Our conventional useage is the reverse--female parent first.  We do not know for certain who followed which pattern among the early hybridizers so parentages and their order is not always certain.
The significant point is--that there have been *no* recorded, recognized doubling of chromosomes or formation of fertile amphidiploids from diploids of any sort that did not involve a disturbed meiosis rather than mitosis resulting in a double-chromosome ovum--or more rarely, pollen grain.  This is true especially of diploid hybrids of oncocyclus X  diploid bearded--a category which includes a number of cultivars with histories sixty, seventy or more years long.  The only possible exception is "William Mohr Giant."
What I find disturbing is the apparent phenotype of "Giant."  The original, authentic William Mohr looks quite oncocyclus-like, has strongly recurved foliage and delicate but very distinct patterning of the *gatesii* type without smearing or shading.  The ground color is quite uniform, and the beard looking quite unlike a normal TB.  The photo of "Giant" does not show these characteristics.  The beard shows some yellow also, which the diploid William Mohr does not as I recall.
If "Giant" is found to be extant it would be a service if a chromosome count were made, and also the number of long metacentric chromosomes noted.  A true, doubled WILLIAM MOHR will have only two.  A "Mohr" "quarter-bred" in the old terminology, will have three.
Neil Mogensen  z 7 near Asheville, NC

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