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

[cwavec]

I have just come across another thread called:

"Disease resistance and what that means"

There appears to be some good information there although I haven't had time
to read much of it.

I'm sure it's relevant to what I asked. Sometimes searching on a topic doesn't
yield much indication of what is actually there, so I request the forbearance of
those who have posted there.

[slugworth]

One year I cloned all the tomato plants that were still alive in my garden in September that survived the blights and planted them the next year.
None performed any better than fresh plants and none lasted til September.
I consider that experiment a failure.So the clones didn't acquire any new disease resistance.

[cwavec]

I started to say:



"That's interesting but nothing to do with the proposed topic...etc., etc."


Yet on the other hand, no one seems to know the limits or parameters ofthis SAR hypothesis, how it arises, how long it lasts, how it is identified or
confirmed or through what conditions it persists or does not. Plenty of
papers being written though, taking it as established or as a valid
assumption.

[slugworth]

I purposely went with clones,which are an extension of the original plant over the course of 2 seasons.

[slugworth]

Soil temps play an important role also with disease tolerance/resistance.
I took the soil temperature of plants that were dying and at the time it was 87 degrees F
Plants that had a living mulch are still nice and green even today.
The living mulch actually got diseased instead of the plants, in some cases.
I got an armored garden hose to bury next year to try to keep soil temps down.
Going to pump rain water through it.

[cwavec]

@Slugworth:

I purposely went with clones,which are an extension of the original plant over the course of 2 seasons.

OK, but what did that tell you? Anything about SAR?


I'm not trying to be cynical here. My original question was:

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.

Although this hypothesis seems to be widely accepted, there was a
time when it was not acceptable. That's a big change that nobody
appears to have noticed. I've come across a couple of papers that are
pretty enthusiastic about the idea but nothing that openly says what
it really is.

[cwavec]

@Slugworth:

Soil temps play an important role also with disease tolerance/resistance

Alright, but that is an external factor, isn't it?


This SAR is put forward as an INTERNAL property or capacity of the
plant. So unless you are saying that a diseased plant develops a fever,
so to speak, I don't see how soil temperature is relevant.


I still haven't seen any answer to what I asked.


Maybe it's too much to expect anyone who has done original work on
this to turn up at Tomatoville but that sure would be nice.


Incidentally, which diseases or blights were you observing?