Re: CULT: aspects of rot - long

In a message dated 10/2/2002 8:26:51 PM Central Daylight Time, 
donald@eastland.net writes:


> Bill,
> 
> >> How far along had the rot progressed?
> >
> >The rhizome was thumb size, the variety was Peace and Harmony. The
> >progression is about 25%. The foliage had not yet deterioated. Also of
> >interest is the point at which the rot begins, or at least where it
> surfaces.
> >It starts 1/3 of the rhizomes length form the oldest end of the rhizome.
> The
> >rhizome itself has only a minute wound where it was detached from the
> mother
> >rhizome with that joint being almost completely matured at the time of
> >detachment. It now appears to be attempting to generate leaf tissue from
> that
> >end.
> >
> >I will post a picture to iris pictures.
> 
> O.K.  I viewed the photo.  Out of the ground for a while.  Should've been
> quite dry before the rot set in it would seem. 

Yes, out of the ground for a while plus the ground it was in had extremely 
low moisture content (zero visually) and and was a pourous soil of 6.5 pH.

Else the rot would have > progressed further by this time.  So how does Erwini 
> manage this?Does it>  require only the moisture in the rhizome itself?

This has been a suspicion here for some time. The example we are discussing 
supports but does not prove the suspicion. Careful examination of the roots 
extending from the rhizone show them dead on each side of the infection and 
progressively more healthy as the distance from the infection increases. 
  
If so, then drying the
> surface would seem to be effective only if the rot has not progressed any
> deeper than the surface.Does it have some kind of feeding network where it
> can invade healthy appearing tissue before it becomes apparent?

I'm assuming the surface of which we speak is the infected surface. And I 
expect you are largely correct. A surface treatment is exactly that a surface 
treatment unless the treatment somehow feeds on the bacteria rather than 
kills on contact. Too, some treatments dry the moisture content of the 
rhizome thus depriving the bacteria of some of an essential necessary for its 
growth.  I suspect, but certainly do not know, the progression through/within 
the rhizome travels the same path as the moisture or perhaps attacking cell 
walls along that path.

> I think the post from Steve indicates the genetic factors involved could
> potentially be really complicated.  If multiple modifiers are at work and
> different modifiers work/don't work under different types of stress, then 
> it
> is going to be very hard to identify cultivars that are truly rot 
> resistant.
> A theory that's going to be hard to prove one way or the other.

I suspect we are dealing with multiple modifiers/genes or at least a 
multiplicity of interrelated facilitators contributing to Erwinia 
susceptibility.

  If my > growing conditions were more consistent, then that task might be 
> easier.
> Here things vary widely - measured in hours at times, much less days, weeks
> or seasons.  I think this may be a Zone 7 characteristic.  Perhaps the
> variations aren't as great in other zones.  At least when I lived in Zone 
> 8,
> while they were often not very amenable to growing things, what occurred 
> was
> certainly more predictable.
> 
The great variability in your (our) growing conditions give us the best field 
testing environment available provided our objective in acquisition of 
knowledge with which to solve problems. Don't see much way to get rich as 
commercial growers though. <g>

Im not through thinkin' but I know we need some academic/lab/field research 
on the soft rot issues. Your/My/Others questions are already enough to keep a 
fair to midlin' size highly educated research staff busy.

We may be able to collect some genuinely, useful data to help zero in on the 
problem. Without some help we are not likely to be able to solve the problem.

If we could find enough disciplined people (volunteers) to plant a bed with a 
prescribed population of single rhizomes of specific varieties, examine each 
member of that population each day (or nearly so) for a one year period. 
Record the temperature, soil moisture content, humidity, rainfall and record 
the earliest observable incidence of soft rot for each, we could answer some 
of the rot questions definitively. This should be done over a wide range of 
growing conditions and latitudes.

We could plot a temperature time line, a humidity time line, a soil moisture 
time line, for each variety in the population within relatively narrow 
latitude ranges. Conceivably we could find published Erwinia growth data 
under the same parameters for comparison to our collected data.

This should draw a pretty good picture of the conditions under which rot is 
eminent in susceptible cultivars.

Dreamin' some while thinkin' some,
Bill Burleson 7a/b
Old South Iris Society


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