Information and discussion regarding garden diseases, insects and other unwelcome critters.
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#1 |
Tomatovillian™
Join Date: May 2016
Location: PA - 5b
Posts: 92
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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 |
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#2 |
Tomatovillian™
Join Date: May 2016
Location: PA - 5b
Posts: 92
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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. |
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#3 |
Tomatovillian™
Join Date: Oct 2014
Location: connecticut,usa
Posts: 1,151
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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. |
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#4 |
Tomatovillian™
Join Date: May 2016
Location: PA - 5b
Posts: 92
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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. |
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#5 |
Tomatovillian™
Join Date: Oct 2014
Location: connecticut,usa
Posts: 1,151
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I purposely went with clones,which are an extension of the original plant over the course of 2 seasons.
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#6 |
Tomatovillian™
Join Date: Oct 2014
Location: connecticut,usa
Posts: 1,151
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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. |
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#7 | ||
Tomatovillian™
Join Date: May 2016
Location: PA - 5b
Posts: 92
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@Slugworth:
Quote:
I'm not trying to be cynical here. My original question was: Quote:
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. |
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#8 | |
Tomatovillian™
Join Date: May 2016
Location: PA - 5b
Posts: 92
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@Slugworth:
Quote:
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? |
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