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Re: mesopotamica influence (rather long)

  • To: Multiple recipients of list <iris-l@rt66.com>
  • Subject: Re: mesopotamica influence (rather long)
  • From: "Jeff and Carolyn Walters" <cwalters@digitalpla.net>
  • Date: Sun, 22 Feb 1998 20:32:45 -0700 (MST)

Celia Storey writes:
> >
> Jeff, LLoyd et al: Tell me if I have followed this thread: I mesopotamica
> in a plant's genetic heritage makes the iris more likely to stay green
> continue growing in mild winters, and more likely to suffer frost damage
> sterner winters. Is that the idea?
> If so, can we Southerners with our mild winters go out into our gardens
> "spot" the I mesopotamica g-g-g-g-g-babies by their lavish winter growth?
> For instance, I am looking at a massive clump of LATIN HIDEAWAY that has
> multiplied and thickened like nobody's business since September. To trace
> its ancestry would take an hour or more of thumbing R&I checklists, which
> I'm not keen to do. Can I posit from the plant's behavior that it must
> mesopotamica genes? Or are there other ancestors that produce the same
> to grow after the winter cooldown (and thus confound glib analysis such
> I am readying myself to pronounce the first time a fellow iris lover
> my garden and spots that mess of LH)?


Modern Tetraploid TBs were created in the first third of this century by
crossing diploid bearded iris of European origin basically derived from I.
pallida and I. variegata with naturally occurring tetraploid forms found
growing in the Middle East. Because of unreduced gametes a fair number of
the offspring from these crosses turned out to be tetraploid rather than
the expected triploids, and voila! - the modern TB was born. Winter
dormancy was a character of the European species, perhaps most marked in I.
variegata; a tendency to grow through the winter (and go dormant or
semi-dormant in the summer) was a character of the middle Eastern forms,
perhaps most marked in I. mesopotamica. Each of these characteristics was
an adaptive adjustment to prevailing environmental conditions in the areas
where these different forms were endemic.

Modern TBs therefore have had an opportunity to inherit any of these
characteristics or some combination thereof. I don't think you could find a
modern TB cultivar that didn't have some I. mesopotamica in its ancestry,
but whether it expresses a genetic tendency towards a lack of winter
dormancy inherited from I. mesopotamica is another question involving the
random assortment of gametes and the selection for and against different
genotypes over the intervening generations. 

Logically, if a modern TB is descended from ancestors which have been bred
and selected in California or Australia for the past 70 years, it might
tend to show a lack of winter dormancy because in those climates winter
dormancy confers no advantage, and may do just the opposite. TBs that are
descended from ancestors bred for the same length of time in areas with
alternating freezes and thaws during the winter might be expected to have
had the tendency to lack winter dormancy bred out of them, since such a
charateristic would be a marked disadvantage under such conditions. Reality
is more messy, of course, since breeding stock has been passed around from
one region to another repeatedly over time.

So, to answer your question, I would say, yes - a modern TB that lacks
winter dormancy most probably inherited that trait from I. mesopotamica or
a near congener such as RICARDI (I suppose there is also the possibility of
some aril ancestry to consider), but another cultivar with as much
mesopotamica in its ancestry could be rock solid winter dormant because
genes influencing the lack of dormancy have been weeded out over time by
chance and/or selection.

Jeff Walters in northern Utah  (USDA Zone 4, Sunset Zone 2)


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