Re: CULT: Leaf Removal & Soft Rot

In a message dated 2/18/2003 1:06:50 PM Central Standard Time, 
lmann@volfirst.net writes:
> 
> But does that have anything to do with soil pH or only pH of the medium
> where the bacteria proliferates (i.e., rhizomes & leaves)?
> 

At the least from a practical standpoint it does. While I've not seen 
controlled research measurements of the pH levels of live iris tissue, 
measurement here suggest it is close to seven. Too, I'm reasonably sure but 
do not know for a fact that variations would be found in different parts of 
plant cell tissue if one is capable of and so inclined to measure. We do know 
with certainty that, once infected, a rhizome will support the bacteria's 
growth if other conditions necessary for it's growth are present. It is not 
uncommon to see the see a host completely consumed in a few days under ideal 
conditions.

As gardeners we are more often dealing with averages and probabilities rather 
than absolutes. Also, our use of the information available to us is more an 
exercise in logic than one of applied science. Accept for the moment that pH 
is an average and Erwinia caratovora is in our soil. For the sake of argument 
here let's also accept the research that specified the pH levels at which 
Erwinia c. can grow.

Applied to microorganisms is a vocabulary of terms used to describe their 
growth (ability to grow) within a range of physical conditions. A thermophile 
grows at high temperatures, an acidophile grows at low pH, an osmophile grows 
at high solute concentration, and so on. Erwinia is non-spore forming and 
facultatively (exhibiting an indicated lifestyle under some environmental 
conditions but not under others) anaerobic (living, active, occurring, or 
existing in the absence of free oxygen ) as per at least one source sources.

"This bacteria ... Erwinia can colonize and survive on hosts at low 
populations. However, it can also invade and cause disease with potentially 
dire consequences. What triggers the decision to invade? It has been proposed 
that during low population growth the bacteria do not wish to express genes 
that could also trigger a defense response in the host (i.e. those that 
attack host tissues). When conditions for the bacteria improve (i.e. the host 
becomes compromised in some manner) they will begin to increase their total 
population and this increase will allow cell-density dependant systems to 
activate expression of products that attack the host tissues. Under these 
conditions they will no longer be as susceptible to host defenses as they 
were at lower cell densities." If this is true and it may not be, the 
question becomes how might we alter the bacteria's enviorenment in such a way 
that retards the signaling process? Logic suggest that pH control might be 
the answer and this might be the reason for my experiences here in higher pH 
level beds.

Logic suggests further that the higher the concentration of Erwinia c. in the 
soil/on the plant the more probable damage from Erwinia will occur. Even from 
a micro world within the soil structure that will support Erwinia c. (more or 
less an opportunist) it must first get/be at a point of attack where it can 
infect the plant to cause harm. Too, it must be present at the point of 
attack when the plant is vulnerable. This would be true regardless of the 
cause of the breach in the plants defenses or the time period over which it 
is vulnerable from such breaches.

Smiles for a thought provokin' question,
Bill Burleson 7a/b
Old South Iris Society

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