CULT: evaluating disease resistance

I've posted a series of photos of irises with various sensitivity to
disease here.  I believe this is soft rot, but have heard others
describe this appearance as due to other causes.  Regardless of cause, I
am trying to develop seedlings that are resistant to it.

In my experience, cultivars exhibiting reddish brown shriveling of leaf
tips eventually will succumb to rot here.  This does <not> look the same
as browning of leaf tips due to drought or sudden freeze, which usually
affects <all> leaf blades in the fan the same way.

Cultivars and seedlings that have this kind of damage may survive and
bloom here if the weather is just right.  They may even thrive for a
time, but when the weather doesn't suit them (i.e., hot, humid, and
several inches of rain every few days), will develop rot in the base of
the fan.  If untreated, the rhizome will often. Sometimes they grow fast
enough that increases will live to bloom another day.  Sometimes the
plant is lost.

The sickly things in the photos are my seedlings - no hybridizers
outside my own garden created these gems :-(

Those reddish brown, shriveled leaves are what I look for (to avoid)
when I am looking at cultivars growing in other people's gardens.

But when I went to take photos of examples, I discovered that the
<majority> of cultivars had some extent of this kind of foliage, thanks
to the constant rain and heat this summer.  I realized that when I am
evaluating foliage, I am subconsciously comparing it to foliage on other
cultivars in the same growing conditions, using some cultivar I know as
a reference point.

In the examples I posted, ICE CREAM SOCIAL and my "super tough" seedling
each has up to 9 leaf blades per fan that are unaffected by disease.
Nice & green.  I found this to be true of all cultivars that I consider
supertough here.  At most, only one leaf blade on each side of the fan
was affected.

On the unhealthy ones, there were as few as 2 or 3 leaf blades that had
no indication of damage.  Some had as many as 3 leaf blades on <both>
sides of the fan affected and the green blades were 'wet' looking.

One of my favorite "reference plants" is IMMORTALITY.  Comparing its
foliage to that of seedlings lets me know that most of those puny plants
I photographed will not live to blooming size.  Or more likely will
bloom, but will rot immediately afterwards.

This is what I'm actually wishing I could see in convention photos.  If
each display garden had IMMORTALITY growing in it for comparison, and if
plants were <not> groomed, photos of foliage (with IMM foliage as a
"control") would help me tremendously in finding new cultivars to try
here.

Even if flower beds were groomed, the relative number of green leaf
blades would probably provide enough idea of health for my needs.

Thanks to Betty for pinning me down on exactly what it is I'm looking
for.

--
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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