HYB: Colchicine & the Triploid Route

Maureen Mark wrote:

>  Colchicine works by inhibiting cell division after chromosomes have
>  duplicated.  However, the resulting tetraploid cell may not be stable.=


Quite true.  This is why converted tetraploids are only used as breeding
stock -- not introduced.   The second-generation tetraploids that are
produced by converted plants ARE stable, however, and may be worthy of
introduction or serve as valuable breeders even if they aren't worthy of
introduction.  =


I haven't used colchicine myself.  I started exploring what John Holden
dubbed the "Triploid Route" many years ago after correspondence with Gene=

Hunt about how he obtained some of his breakthroughs -- and found it
well-suited to my purposes.  I don't mean to discourage anyone who wants =
to
experiment with colchicine, taking suitable precautions, just present a
non-chemical means of capitalizing on the breakthroughs already made.

The Triploid Route was so named because the process uses triploids to
provide a conduit for transporting genes from diploid stock to the
tetraploid gene pool.

1.      Cross diploids having desired genes with the best available
tetraploids.

2.      Cross the resultant triploids back to tetraploids.  At this point=
,
fertility is limited so I save ANY seedling that produces offspring.  I
also save any that are remarkable, in hopes they might later produce a
seedling or two.  Don't expect any to be fully fertile, but watch for suc=
h
an anomaly because once-in-a-while an unreduced gamete will result in a
first-generation tetraploid.

3.      Cross the second-generation seedlings back to tetraploids.  Yes,
EVERY second-generation seedling.  Not as hard as it sounds because there=

aren't many.  Repeat the selection process with respect to both fertility=

and desired characteristics.  In theory, about half should prove fully
fertile and half should be limitedly fertile. =


The third, and subsequent, generations will be predominantly fertile.  =


Sharon McAllister
73372.1745@compuserve.com
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