Re: Re Triploids
- To: Multiple recipients of list <i*@rt66.com>
- Subject: Re: Re Triploids
- From: T* T* L* <t*@rt66.com>
- Date: Thu, 6 Mar 1997 14:37:39 -0700 (MST)
John writes
:Several mentions have been made that triploids are sterile and therefore a
:dead-end in hybridizing. I believe that there are examples in the
:intermediate class which make this statement not strictly true. Is it more
:accurate to say that the work is difficult and frustrating but not impossible?
Your last sentence is absolutely correct. (I never meant to imply that all
triploids are strictly sterile, only that limited fertility is a barrier to
using triploids in breeding.) Many iris triploids have some degree of
fertility, so some breeding can be done, particularly crossing the triploid
with a diploid or tetraploid. However, a family that is entirely triploid
(such as the OGB+ arilbreds created by crossing arilbreds with diploid
oncos) cannot be improved by line breeding the way a fully fertile family
can. Triploidy really is a barrier to improving a class of irises, even
though individual plants can sometimes be used for specific breeding plans.
Incidentally, IBs are not triploids but rather unbalanced tetraploids. They
have three sets of TB chromosomes and one set of pumila chromosomes. The
latter causes trouble during meiosis and causes the fertility problem. As
you mention, IBs do show some fertility, a phenomenon that seems to be
increasingly common in recent decades. This is useful, for example, in
trying to transfer a particular IB trait into SDB or TB lines. But we still
can't effectively line breed IBs by crossing IB x IB and selecting the best
seedlings.
:
:Now to warp my argument a bit, has conversion to tetraploidy been attempted
:for I korolkowii?
There was once apparently a natural tetraploid form that Gene Hunt grew.
Last year, Sharon told the sad story of its disappearance. Work with
converting arils to tetraploidy has focused on the oncocyclus and
oncogelias. I haven't heard of any attempt to convert korolkowii. It would
be nice to have, but if someone were going to the trouble, I'd rather see
them work on some of the most spectacular oncos, such as lortetii or
gatesii.
Happy irising, Tom.
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Tom Tadfor Little telp@Rt66.com
Iris-L list owner * USDA zone 5/6 * AIS region 23
Santa Fe, New Mexico (USA)
Telperion Productions http://www.rt66.com/~telp/
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