Re: MDBs continued (and an MTB question to boot.)

Rusty wrote:

>  I am also interested in the "problems" that Mike Lowe mentioned when h=
e
>  talked about MTB's dipoid to tetraploid hybridizing.  I would like to
>  try crossing Sindjka to modern irises, and hopefully get a modern
>  version.  Aside from the time it takes to include those genes in a lin=
e
>  of fertile tets, what are the other problems???

The main problem is getting seedlings that meet MTB criteria for flower a=
nd
stem size.  You can outcross to TBs, then back-cross and line-breed to ge=
t
seedlings that grow in class -- but this is a long-term program.  If you
have time and patience, though, it is quite doable.  =


Please don't be discouraged by warnings that what you propose is a
long-term program.  Twenty years ago, I was told by people whose expertis=
e
I respected that the program I was starting would take 40 years to
complete.  Time has proven them right -- IF I had done it exclusively by
line-breeding.  But by working with parallel lines I've already
accomplished most of my goals.

With MTBs, there are other alternative approaches you can use at the same=

time you experiment with outcrosses to TBs:

1)      Cross diploid MTBs with tetraploid MTBs.  This is the first step =
of
the Triploid Route I've described.  It capitalizes on the breakthroughs
others have already made.  =


2)      Cross diploid MTBs with historic diploids.  Some of these were
originally classified as TBs but come very close to meeting today's
standards for MTBs.  =


As long as you are aware of ploidy, working with diploids, triploids, and=

tetraploids can be an advantage.  It's a disadvantage ONLY if you're
working without information.

I don't have a chromosome count for SINDJKA, but I can offer some practic=
al
advice for working with such historics:

If you find a gracile, historic TB (one that looks enough like an MTB to
tempt you to use it) and you don't know it's count -- it's most likely a
diploid.  But you don't have to assume anything because you can find out
with test crosses.  Cross it with both diploid and tetraploid MTBs.  If i=
t
is fully fertile with diploids, use it like a diploid in future crosses. =

If it is fully fertile with tetraploids, use it like you would a
tetraploid.  If it is partially fertile with either, treat it like a
triploid.

IMO, getting a fertile diploid MTB with the desired characteristics is ju=
st
as good as getting a fertile tetraploid.

Sharon McAllister
72271.1745@compuserve.com
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