Breeding tetraploid medians and dwarfs
- To: Multiple recipients of list <i*@rt66.com>
- Subject: Breeding tetraploid medians and dwarfs
- From: T* T* L* <t*@rt66.com>
- Date: Sat, 1 Mar 1997 16:30:11 -0700 (MST)
When I returned to "irising" in 1993, the line of breeding I was most eager
to take up was expanding the race of 48-chromosome medians. Ben Hager got
the ball rolling on this project long ago, and the Craigs have taken it up
with a vengeance. Now others are also working in the area, particularly in
breeding tetraploid MTBs.
Why is this an interesting line of work? Because currently, median breeding
is dominated by the SDBs, which are fertile advanced-generation hybrids
between TBs and I. pumila. The SDBs were a great breakthrough, but because
pumila and TBs have different chromosome counts, you can't backcross the
SDBs with either pumilas or TBs and expect fertile offpsring. Hence the IB
(SDB x TB) and MDB (SDB x pumila) classes are very hard to line breed. Most
breeders treat these sort of crosses as one-shots, and are extra careful
selecting parents, because there will probably be no second generation. The
48-chromosome tetraploid medians, however, can be line bred with the TBs
and with each other. That seems like an opportunity for interesting work.
Also, these tetraploid medians could be used for making fertile arilbred
medians (by crossing with tetraploid arils) and fertile MDBs (by crossing
with pumila).
That's the why, how 'bout the wherefore? Those working on these lines have
used I. aphylla almost exclusively. It is a rock-hardy, copiously branched
bearded species, with forms in the SDB and IB height range, most taller
than a good SDB would be. Most of the medians produced from crossing
aphylla with TBs or BBs (to improve the form and color range) thus tend to
shake out into the IB, MTB, or BB classes. Recently, the Craigs have had
some small segregates from these lines that fit the SDB class.
My great plan was to use the MDB-sized tetraploid species Ii. balkana and
reichenbachii with TBs or BBs, in the hopes of getting more small
tetraploid medians, in the SDB or MDB height range. I. balkana has already
been bred into some TB lines, so it can work. Those who used it, however,
were not particularly interested in selecting small plants from the
breeding line. That's what I wanted to do.
The problem is that I have not been able to locate any plants or seeds of
these species. The clone "balkana Darby" is a verified tetraploid and was
available from several different places 15 years ago. Now it seems to be
playing hard-to-get. I. reichenbachii apparently has both tetraploid and
diploid forms, and is also hard to come by. (Mathew considers balkana a
synonym for reichenbachii, but whatever it's status, "balkana Darby" is the
plant I'm most interested in using.)
If any of you have seen these species offered for sale, or know any
collectors of bearded species who might have them and be willing to share,
I'd be very grateful for the information. I have actually seen them listed
a couple places over the last three years, but when I try to order I find
that the grower's stock did not produce well enough to sell.
I actually grew and bloomed balkana Darby 15 years ago. Alas that my iris
growing was rudely interrupted by my career in the interim.
In the meantime, I'm hoping to use the Craigs' smaller intros to start my
line. But I doubt if there's much I can do with them that they haven't
already done.
Happy irising, Tom.
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Tom Tadfor Little telp@Rt66.com
Santa Fe, New Mexico, USA
Telperion Productions http://www.rt66.com/~telp/
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