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Joel Grossman's Excellent Post (fwd)
---------- Forwarded message ----------
Date: Wed, 12 Apr 1995 07:03:28 -0700 (PDT)
From: Tom Hodges <thodges@beta.tricity.wsu.edu>
To: "Tom Hodges (moderated newsgroup)" <sustag@beta.tricity.wsu.edu>
Subject: Joel Grossman's Excellent Post (fwd)
---------- Forwarded message ----------
Date: Wed, 12 Apr 1995 00:11:31 -0700 (PDT)
From: Charles Benbrook <benbrook@hillnet.com>
To: sanet <sanet-mg@ces.ncsu.edu>
Cc: benbrook@hillnet.com
Subject: Joel Grossman's Excellent Post
Geez, SANET has had some really good posts lately. Joel -- thanks for
adding some important details to discussion of disease suppressive
soils. I too have looked long and hard through the literature in about
20 disciplines, talked to many experts, spent lots of time with farmers
who know the difference between a disease suppressive soil and one which
just does not seem able to slow down nematodes and pathogens.
My research/contacts lead me to a plausible explanation of why
the unfumigated trees catch up with the fumigated ones. Scientists have
now documented at several levels, in many crops, a phenomenon called
systemic acquired resistance. This is the mechanism whereby a plant
attains a strong, or high degree of capacity to express its inherent
potential immune response, its ability to withstand or overcome pest or
stress attacks. Systemic acquired resistance (SAR) is sort of like a
mammals response to allergy shots; to "work", or to happen, a plant must
be exposed to some level of a pathogen early in its growth, when its
immune system is, in effect, being turned on and stretching to
accomodate, as best it can, the threats it thinks it will encounter in
its environment. A plant or tree's immune response is, in effect, fully
formed after it goes through early maturation. If the plant/tree is not
subjected to a pathogen when its immune system is "growing", or gaining
the capacity to "kick in" in response to particular pathogen pressure, it
will never be fully able. It is a "need it early and use it early,
or lose the capacity to develop it" phenomenon. This much we know.
So, my guess is that plants/trees growing up in fumigated soils
are not exposed to the low levels of pathogen attack needed to stimulate
SAR. Hence such plants may grow well early on in the abscence of pest
pressure, but later on when they SHOULD NATURALLY BE ABLE TO WITHSTAND a
degree of pressure, they are immunological weaklings, having lacked the
chance to "grow up with" the pathogens that are a normal part of their
environment.
I have some other more cmplex ideas/theories about mechanisms
through which SAR is triggered, and how different management systems
affect it, but this is not the time or place. Anybody encountered such
an explanation before? Bob Goodman at Univ. Wisconsin plant path. dept,
Joseph Kuc at Kentucky are two of the brightest, most broadly
knowledgeful people on SAR and farming systems. Several excellent papers
have been published in Science and elsewhere describing the mechanism.
It is fascinating science, and lies at the heart of disease suppressive
soils. My guess is that the capacity of a soil to suppress disease has
as much to do with how soil microorganisms trigger plant physiological
processes, especially SAR, as it does about microbial biocontrol of plant
pathogens.