Re: Re:Auto-tetraploid versus amphidiploid was Hyb spots
iris@hort.net
  • Subject: Re: Re:Auto-tetraploid versus amphidiploid was Hyb spots
  • From: B* C* <b*@ymail.com>
  • Date: Thu, 28 Feb 2013 09:40:34 -0800 (PST)
I have been doing a LOT of aphylla bred MTB X TB crossing (using the tet MTBs
from the Craigs, Hager or Fisher).  I have also been doing some aphylla bred
MTB X SDB and aphylla bred MTB X IB.  One observation from my work and also
from Vicki Craig, is that seed counts and germination of the crosses with the
SDBs and IBs is lower than with the TBs, but germination will improve if you
hold seed pots for a second year.  I also see this with diploid X Tetraploid
crosses.  The aphylla bred MTB X TB crosses produce seed counts and
germination rates equal to TB X TB for me.

Bill Chaney
________________________________
 From: Chuck Chapman <irischapman@aim.com>
To: iris@hort.net 
Sent: Thursday, February 28, 2013 8:46 AM
Subject: [iris]
Re:Auto-tetraploid versus amphidiploid was Hyb spots
 
We had been discussing 
aphylla  X TB hybrids and fertility.

Actually, it turns out that full
tetraploids, (autotetraploids) with  four identical  genes, have much reduced
fertility compared to amphidiploids, or straight diploids.

This is because 
during meiosis (forming of  gametes, eggs and pollen)  four sets of identical
genes often form tetravalents. And during first stage of meiosis,  either all
of these four genes go into  one cell, or the other, leaving no copies in the
other cell. When there is  small differences in the  four sets of genes, of a
particular chromosome, you get two  bivalents and  so proper  division during
meiosis

Now remember,  most tetraploid iris, at least the TB iris , have
multiple  species involved  in their creation, so probably a number of  genes
from different species, with enough of a difference, and enough of a
similarity, to pair up as fertile bivalents , rather then tetravalents during 
meiosis.

Also almost all ( I'd say all, but there probably an exception or
several out there somewhere) fertile tetraploids found in nature, are a result
of an inter  species hybrids, and thus are  amphidiploids, rather then
autotetraploids.

So fertile 4x 48  iris are should basically be considered
amphidiploids. The infertile ones are probably autotetraploids.

Look up
"fertility in autotetraploids"

Chuck Chapman
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