Re: HYB: seedling survival comparisons

Walter - Thanks so much for sharing so much detailed information &
examples!  <Much> food for thought.  A few of the first thoughts that
come to mind....

Another aspect of disease resistance that I read about sometime in the
not too distant past (and may have posted something about), had to do
with changes that occur in defense mechanisms in (some? all?) individual
plants when exposed to pathogens (and other stressors?).  The question
came up when we were discussing whether or not a given cultivar could
"adapt" to different stressors when moved from one climate/soil/care
regime to another. Once some plants have diverted resources to defense,
they keep them that way, so if the stressor re-appears, they are "ready"
for it.  Others only develop defenses in <response> to stressors, then
stop once the stress is gone.  As I recall, both mechanisms can be
present.  I don't know if all species are capable of both, but my
personal experience with irises makes me think one mechanism or the
other tends to predominate in some cultivars.

The ones that thrive here seem to have mostly the 'always ready'
approach.

But those are mature rhizomes.

From what you've said, I'm definitely eliminating seedlings that don't
have that initial disease resistance already present in the plant.  I am
also eliminating most of the latter type after seedlings are lined out
in the garden.

But there is a third factor that affects survival of my seedlings -
ability to recover from transplanting from seed germination pots into
larger pots for growing on during the winter.  Some of this may be
disease resistance/tolerance, some may be growth, or maybe it all has to
do with what the seedling is doing with resources (repair, defense,
growth).

I definitely over-stressed that one afternoon's batch of transplants -
the "sun" porch is a tiny room, it was too cold, I forgot to leave the
door into the house open to moderate temperature & humidity, several
enormous tender salvias were out there pumping huge amounts of moisture
into the air, condensate was almost dripping down the windows - you get
the idea.  Most died, a few survived, a few entire crosses survived
well.

The crosses with the highest losses had at least one parent that is weak
(i.e., lucky to bloom and get pollen) here.

Another factor may have had to do with stressing seedlings just as they
were finishing up the last of food reserves in their seeds.

As for small populations, the ?good news is that crossing two of my
healthy seedlings (which I'm just barely starting) produces larger
numbers of seeds, higher germination rates, higher survival rates than
crosses involving cultivars not adapted to my growing conditions.  Less
healthy seedling crosses also produce more seeds and higher germination
rates, but not higher survival rates.

The bad news is that I am still at the stage of having to use other
people's seedlings (introduced and otherwise) that are <not> necessarily
adapted to my growing conditions while I search for good combinations
that will produce both good performance and good blooms here.  I will go
thru my notes and see what percentage of crosses have produced either
healthy plants or nice blooms.  Not many with both.  Yet! <g>

Thanks again, Walter.  Very helpful information, & encouragement for all
this mayhem <g>

  <Some forms of disease resistance is based on chemistry inside the
plant cell, and is going full blast as soon as the seed starts to
germinate.  Other forms of resistance are based on thick skin with
specialised chemicals in the skin, which will develop later.
                     For the former, infecting the seedling, or even
germinating the seeds in filthy conditions, will indeed select for the
genes controling single cell resistance.  If such genes are present.
                     For the latter, selecition will be ineffective
until the plant is well established.
                     I suspect the latter is more important in
iris........
Studies in grain showhigh value in selection under adverse conditions.
But they generally had multiplication in alternate generations under
excellent conditins so there would be lots of seeds to plant in the next
generation in the adverse conditions again.
                     Walter>

--
Linda Mann east Tennessee USA zone 7/8
East Tennessee Iris Society <http://www.korrnet.org/etis>
American Iris Society web site <http://www.irises.org>
talk archives: <http://www.hort.net/lists/iris-talk/>
photos archives: <http://www.hort.net/lists/iris-photos/>
online R&I <http://www.irisregister.com>

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