From: Charles Benbrook <[email-masked]>
Date: Mon, 18 Apr 1994 08:15:50 -0700

4/18/94
Note to Sanet --
From:  Chuck Benbrook
 
     A very important article has recently been published as a
letter in the journal "Phytopathology" (Vol. 84, #3, 1994, pages
222-225), entitled "Root Camouflage and Disease Control" (by
Gregory Gilbert; Jo Handelsman; Jennifer Parke).  It explains a
mechanism whereby certain soils can become disease suppressive. 
The implications are exciting, and make a great deal of sense in
light of the insights emerging in the growing literature on
microbial biocontrol of plant pathogens.  While there has been a
resurgence of interest in disease suppressive soils (actually,
farming systems that render plant-soil interactions less vulnerable
to yield loss caused by disease), there is little understanding of
the mechanisms within soil microbial communities that give rise to
observed instances in which some soils, under certain
circumstances, become disease suppressive.  Scientists world wide
are searching for answers to what characterizes a disease
suppressive from a disease supportive soil, for obvious reasons
(they want to replicate via management or an input the state that
gives rise to disease suppressiveness).  The above letter provides
a cohesive explanation for a process that may, in fact, be one of
the major mechanisms of disease suppressiveness.
     I don't want to spoil the show or steal their punch-line, but
the letter explains the differences between bacteria populations in
the rhizosphere in contrast to root-free soil.  Certain ubiquitous
pathogens are clearly "turned on by" the exudates and other
microbial activity unique to the rhizosphere.  But when the
microbial activity in the root-free portions of the soil profile is
closer to the activity in the rhizosphere, pathogenic
microorganisms seem less inclined to attack roots, hence the use of
the word "camouflage" in the letters title.  Any management
practice that elevates general microbial activity and complexity
throughout the soil profile will tend to contribute to this effect. 
I recommend this article to anyone interesting in the science base
of disease suppressive farming systems.  And congrats to the
authors for breaking some real ground!