Systemic Acquired Resistance (SAR)

[cwavec]

Systemic Acquired Resistance (SAR)

What is this?

What is going on here?

Not so long ago you couldn't talk very much about the resistance of
plants to disease and still be accepted in polite horticultural
circles. If you persisted in so speaking, you would soon be corrected
and instructed on the difference between the words "resistance" and
"tolerance". Plants could not "resist" disease in any meaningful way
although certain cultivars might have a degree of "tolerance" to
some disease organisms and were therefore more desirable and the
object of significant amounts effort in research and breeding.

Now, however, the focus seems to have shifted and it has become
acceptable to talk of resistance, including a property called
"Systemic Acquired Resistance". I have seen a couple of academic
papers on this topic, including one mentioned by Tomatovillian
PdxMatos*

The drift now is that plants can actually resist the attack of
pathogens by producing compounds which either counterattack the
pathogen or convey an ability upon the plant to resist the activity
of the pathogen. Sometimes this is even characterized as an
"immune response". Moreover, these compounds can be translocated
within the plant to bring a degree of resistance or immunity to
parts of the plant that are not infected.

Not only that but sometimes manufactured or cultured factors can
be used to induce this resistance. Some are classed as biofungicides
while some may just be chemicals. Claims have been made about the
properties of these substances:


Bonide:

"Triggers plant immune response" ... "Colonizes roots" ..."Controls
listed blights, molds, rots, spots and mildews".

Bayer:

"Fungicide that attacks harmful garden diseases" ... "Controls
Powdery Mildew, Rust, Gray Mold".

Whether these claims can really be fulfilled seems to be rather up
in the air. In at least one case the manufacturer has lowered the
claim from "control" to "suppression".

I have personally used a couple of these products, either alone
or in various combinations with other products, with results
ranging from nothing to variable and limited effect.


Does anyone here in Tomatoville have an idea about the actual state
of the art with respect to these products and claims or possibly
reference to significant (even early) work and papers.



*"Salicylic Acid Induces Resistance to Alternaria solani in
Hydroponically Grown Tomato", Phytopathology 2007