heterosis and the "rebloom gene"
- To: Multiple recipients of list <i*@rt66.com>
- Subject: heterosis and the "rebloom gene"
- From: T* T* L* <t*@rt66.com>
- Date: Tue, 18 Mar 1997 13:41:01 -0700 (MST)
Yesterday the _RIS Recorder_ came (BTW--great job, Kathy!), and I got to
read Clarence's article on heterosis (hybrid vigor) as a basis for rebloom.
Good stuff--recommended reading for anyone who hybridizes, not just those
working with rebloomers.
Clarence's hypothesis is that crossing irises from widely different lines
of breeding yields seedlings with hybrid vigor, which in turn produces
rebloom.
I agree, but I'd like to suggest that rebloom DOES have a genetic component
as well. There are too many rebloomers with reblooming parents to be
accounted for otherwise, in my opinion. Here's my unscientific hunch about
rebloom.
An iris needs two things to be a reliable rebloomer:
(1) A defective biological clock(s). Most irises *know* when they're
supposed to bloom, and that is once a year, in the spring. (Look at the
consistency with which some bloom early and others late.) This timer must
be at least partly disabled in rebloomers. Perhaps different defects
account for different patterns of rebloom (everblooming, fall blooming,
sporadic blooming). I suspect this is genetic, and probably recessive in
most cases--or at least requires more than one dose for manifestation at
the tetraploid level.
(2) Exceptional vigor, so that a clump will have a number of blooming-size
rhizomes ready when the urge comes. This is where heterosis comes in.
(Vigor definitely has genetic components too, but outcrossing is certainly
a reliable way to improve vigor, and inbreeding is a reliable way to
degrade it!)
The defective-timer genes are probably present in a lot of irises that
aren't regarded as rebloomers, because everything that's ready to bloom in
a given year *does* bloom in the spring, and it takes nearly a full year to
make new fully developed rhizomes with bloomstalks ready to grow. (But
growers with mild climates know that some will bloom unexpectedly early in
the year--January or February.)
We can also all probably think of irises that have extraordinary vigor
(more than some reliable rebloomers), requiring frequent division, and yet
never rebloom. (I know a lot of arilbreds that grow this way.) Something
besides vigor is clearly required and missing in these irises.
Comments? Maybe Lloyd will have something to say, if he hasn't begun to
aestivate yet.
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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/
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