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Re: MDBs continued.

  • To: Multiple recipients of list <iris-l@rt66.com>
  • Subject: Re: MDBs continued.
  • From: Tom Tadfor Little <telp@rt66.com>
  • Date: Tue, 2 Sep 1997 14:24:34 -0600 (MDT)

Ryan wrote

>        As a follow-up to my question about reblooming MDBs, (this may seem
>like a stupid question to ask but...) what other developments are there to
>be made in that field (i.e. color, form, hardiness, diploid-to-tetraploid,

This is a great question, one close to my own heart. First of all, this is
wide open field. There are not many hybridizers of MDBs, and most of them
don't have planned breeding programs, but just take advantage of
opportunities as they appear.

Virtually all the MDBs are tetraploids, but several different kinds of
tetraploids are present. Understanding this is the key to planning a
successful breeding program.

First, there are MDBs that are pure Iris pumila. This diminutive species is
in the background of most MDBs, SDBs, and IBs today. It is unbranched,
typically 3 to 4 inches tall, and very early blooming. There aren't too
many pure pumilas available on the market now. With effort, I've been able
to build a collection of less than a dozen. These are 32-chromosomes
tetraploids. I use the notation PPPP to represent their four sets of pumila
chromosomes. These are generally fertile, especially amongst themselves,
although I find the vagaries of early spring weather often foil my attempts
to hybridize on them, and they are so small that their tiny pods don't hold
the massive quantities of seed you may be used to with TBs. Pumilas require
lots of winter cold to survive and bloom well. Examples: Baby Tiger, Daring
Eyes, Buzz Bee.

Next, there are the MDBs that have the same chromosome breakdown as the
SDBs: two sets of pumila chromosomes and two sets of tall bearded
chromosomes, PPTT, for a total count of 40. Most of these are "unplanned"
products of SDB breeding, which just happen to be small enough to fall in
the MDB class. MDB pinks and plicatas are essentially all in this category.
They are the most adaptable MDBs for warm climates and tend to bloom late
in the MDB season. These are also quite fertile, and obviously breed easily
with the SDBs. The problem, of course, is that since these are basically
small SDBs, they tend to produce seedlings that are too large for the MDB
class. Examples: Ditto, Fairy Lore, Knick-Knack.

Finally, there are MDBs that come from SDB x pumila crosses. They end up
with three sets of pumila chromosomes and one set of TB chromosomes: PPPT,
or 36 chromosomes altogether. They are less fertile than the other two
types, but in many ways they combine the best of both parent types: lots of
different color patterns, reasonable performance in various climates, and
reliably small size. They would be ideal for a breeding program, were it
not for their limited fertility. Examples: Crocus, Zipper, Alpine Lake.

[Knowing which MDBs are in which category usually requires some pedigree
research. I have a fairly complete list of 32-chromosome pumilas, and I'm
working on a list of 40-chromosome MDBs. They may end up on my web site
some day.]

I think the future of the class lies with the 40-chromosome group. Unlike
the 36-chromosome group, they have enough fertility to make long-term
breeding plans possible. Unlike I. pumila, they have the added advantage of
color patterns from the TBs and growability in mild climates. The challenge
is to develop a line that produces reliably small plants, rather than 75%
or more SDB-sized seedlings. Ben Hager worked on this for many years, with
significant (but slow) progress. Ben believes (and I agree) that the key to
keeping the 40-chromosome group small is using I.aphylla-based medians,
rather than TBs, in their breeding. In other words, instead of starting
with typical SDBs (which are bred from TB x pumila crosses), use tet MTB x
pumila crosses to start the line. Even doing this (Libation is an example),
Hager found most seedlings are too large for the MDB class.

I think there is now more potential than ever in this line, because the tet
MTBs that have been derived from I. aphylla are improving in quality and
becoming daintier. (The Craigs have already introduced two 48-chromosome
SDBs from these lines.) Using the newest, smallest tetraploid medians with
I. pumila should improve the chances of establishing a line of reliably
small 40-chromosome MDBs. I've made crosses to this end, but am still
waiting to see if they lead to anything good.

So here's the short version:

What needs to be done? Develop MDBs with

- more different color patterns
- more modern form (eliminate tucking and increase width)
- better adaptability to both mild and cold climates
- consistent small size and daintiness
- reliable fertility for line breeding

How to do it?

- start with the current 40-chromosome MDBs (mostly from Ben Hager, but
there are others too)
- get some I. pumila MDBs and cross them with the smallest, newest
48-chromosome medians, such as the tet MTBs
- line breed the Hager MDBs (and possibly some of the daintiest SDBs) with
the pumila/median hybrids, always selecting for small size and modern form

Persisting in the plan for three or four generations should produce a good,
working line of 40-chromosome MDBs, distinct from Hager's but crossable
with it. Such outcrosses can then be made judiciously to enhance vigor and
bring in new desirable characteristics.
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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