Re: HYBR.

:What do I get if I cross an :
:
:SD with an IB   or
:
:SD with an MTB  or
:
:SD with an TB    ???

Hi Gunnar! Welcome back.

First of all, it is important to understand that which median class an iris
falls in depends on how the plant actually grows, not on its parentage. So
any bearded iris that is between 8 and 15 inches tall is an SDB, regardless
of what its parents may have been. But I'll take the question to be: What
kinds of plants are likely to result from these types of crosses?

SDB x IB: As Chad remarked, IBs are generally not very fertile, so this is
not an easy cross. But it certainly can be done, and has been. You can
expect the seedlings to cover a fairly wide range of height and bloom
season. Some will meet the criteria for the SDB class, others will be IBs.
The theory says that you should see two distinctive groups among the
seedlings: some that are clearly SDBs, the others clearly IBs, without too
many "hard to call" cases. Whether this happens in practice, I do not know.
Perhaps one of the hybridizers on the list has some actual experience with
this kind of cross and can share it with us.

SDB x MTB: In appearance, these should not be too much different than what
you would get from the SDB x IB cross, although the cross itself should be
a little easier to make. The MTB parent might help make the offspring
daintier in flower size and stalk proportions. It is unlikely that many of
the seedlings would meet the strict criteria for the MTB class, however. My
guess is that many would be SDBs and some would be IBs, with perhaps
something that would fall into one of the other classes on occasion.

SDB x TB: This is the classic cross for IBs. Even here, though, there is
some variation. A few will be too small or two large for the IB class.

In terms of chromosomes, the SDB has two sets of Iris pumila chromosomes
(which I write as P), and two sets of tall bearded chromosomes (which I
write as T), so

SDB = PPTT

Similarly (these are generalizations, but almost always correct),

IB  = PTTT
MTB = TT (diploid) or TTTT (tetraploid)
TB  = TTTT

So SDB x IB  = PPTT (fertile SDB) or PTTT (IB, probably infertile)
   SDB x MTB = PTT (sterile triploid) or PTTT (IB, probably infertile)
   SDB x TB  = PTTT (IB, probably infertile)

The likelihood of infertility in some of these crosses is a reason they are
not done more often. The SDB x TB cross is popular, though, since it is the
easiest way to get an attractive IB.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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/
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Iris-L Web Site  http://www.rt66.com/~telp/garden.htm
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