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Old July 15, 2019   #1
jhouse
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Default Disease resistance and what that means

I googled this, and mostly found people suggesting which varieties are most resistant.

But what I'm curious about, is what exactly does that mean? Are the leaves of the plant less likely to have the fungal disease spread on it somehow?

Or, are they developed so that they have quickly growing new growth, so that they "outrun" the disease but having plenty of growth as the grower prunes away diseased leaves?

Thanks if anyone happens to know about this.

Jan H.
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Old July 15, 2019   #2
jtjmartin
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Jan:

The mechanism of resistance is often very complicated and hard to explain. Here’s a “non-technical” explanation of bacterial speck resistance:

Non Technical Summary
In tomato, resistance to bacterial speck disease is determined by the resistance protein Prf, a host resistance protein with a nucleotide-binding site (NBS) and a region of leucine-rich repeats (LRR). Prf indirectly recognizes either of two effector proteins, AvrPto or AvrPtoB, delivered by the Pseudomonas syringae pathovar tomato (Pst).

Sometimes the resistance results in less disease growth or the resistance allows high pathogen growth with little damage.
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Old July 15, 2019   #3
bower
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Afaik, I think "tolerance" is when the disease is present but the plant outgrows it or is not affected ie continues to grow, fruit, etc.
Resistance is when the plant is slower to be affected and show symptoms of the disease..
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Old July 15, 2019   #4
brownrexx
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For example, I grow County Fair cucumbers which are bacterial wilt resistant. They eventually get wilt but not until late in the season when I have harvested plenty of cucumbers.

Non resistant varieties die before I get anything. The cucumber beetles transmit this disease.
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Old July 16, 2019   #5
jtjmartin
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Originally Posted by brownrexx View Post
For example, I grow County Fair cucumbers which are bacterial wilt resistant. They eventually get wilt but not until late in the season when I have harvested plenty of cucumbers.

Non resistant varieties die before I get anything. The cucumber beetles transmit this disease.
Similar here but bacterial wilt kills most tomato plants shortly after the first tomatoes start to color.

I graft on to resistant rootstock - most of these tomatoes will last until the first frost with vines well over 20 feet long.

Jeff
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Old July 16, 2019   #6
nctomatoman
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So the best way to consider this is the absolute definition of resistance and tolerance.

Resistance means that the mechanism of the plant resists attack of the agent - in the case of Fusarium, a fungus that moves into the roots from the soil, a F resistant variety means that the roots resist movement of the agent into the roots.

Tolerance means that even though the agent moves into the plants, the plant can tolerate the attack and do reasonably well for a spell after attack.

But here's the thing - the terms are really relative and misinterpreted. In high disease pressure areas, plants won't resist or tolerate the disease indefinitely. For example, let's say you have a Fusarium resistant plant. The plant will resist the disease a bit longer than a non resistant plant, but if the disease pressure is high, it will go down a few weeks later (or some time frame).

So with grafts, if rootstock is highly resistant to this or that disease, in principal it will from some to alot more time. The key then is to use good garden hygiene, keep soil from splashing onto foliage above the graft line, etc - that plant top will be just as susceptible to the disease as an ungrafted plant - the protection is whatever the roots can provide.
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Old July 16, 2019   #7
jtjmartin
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You got me interested so I just read a paper on BW in tomatoes from 2014.

Looks like the resistant root stock keeps the bacteria out somehow - the plants were negative for the bacteria.

Other facts about BW:

Around 2012, over 80% of the tomato plants in Japan were grafted.

A resistant rootstock that works in China might not be effective in the US - the strains of Ralstonia solanacearum can vary.

RS can persist in soil up to 10 years - even with nothing planted!
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Old July 16, 2019   #8
jtjmartin
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Quote:
Originally Posted by nctomatoman View Post
So the best way to consider this is the absolute definition of resistance and tolerance.

Resistance means that the mechanism of the plant resists attack of the agent - in the case of Fusarium, a fungus that moves into the roots from the soil, a F resistant variety means that the roots resist movement of the agent into the roots.

Tolerance means that even though the agent moves into the plants, the plant can tolerate the attack and do reasonably well for a spell after attack.

But here's the thing - the terms are really relative and misinterpreted. In high disease pressure areas, plants won't resist or tolerate the disease indefinitely. For example, let's say you have a Fusarium resistant plant. The plant will resist the disease a bit longer than a non resistant plant, but if the disease pressure is high, it will go down a few weeks later (or some time frame).

So with grafts, if rootstock is highly resistant to this or that disease, in principal it will from some to alot more time. The key then is to use good garden hygiene, keep soil from splashing onto foliage above the graft line, etc - that plant top will be just as susceptible to the disease as an ungrafted plant - the protection is whatever the roots can provide.
Thank you - that makes sense.

My next move - if grafting ever becomes ineffective - would be to move to grow bags with a sterile medium.

Do you replace your medium? Do disease build in it year to year?
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Old July 16, 2019   #9
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Resistance or tolerance, either way the most resistant or tolerant gives the home gardener an extra week or so of healthy plant. I find cultural practices do more than worrying about varieties with tolerance or resistance; soil health, mulching program, proper watering, staking or caging being disinfected yearly...just plain sensible gardening practices.

If I were a market tomato farmer the extra week may mean making a profit or losing the farm. As for me, a few extra tomatoes or cleaning out the garden early by a week is mostly inconsequential. Here we have less problematic disease than many other areas of the country so I worry less than other growers. Still all reasonable precautions are taken other than base my varieties grown on tolerance or resistance.
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Old July 16, 2019   #10
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With grafting in my area it's extra months - not just weeks. I would be growing out of bags if grafting only gave me a week or two.

Jeff
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Old July 16, 2019   #11
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If your grafts are working that well, bravo - you have a great match between what is in the soil as a disease agent, and the particular graft used. Good to know, and great news.

Using bags or bales (both sterile) are great for things like Fusarium and Bacterial wilt, but the air-spread fungi like septoria and early blight are still an issue. Foliage removal and good spacing and keeping foliage dry work well.
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Old July 16, 2019   #12
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So true that it is all about buying some time... Every plant goes down with some funk or other at the end of the season.

Resistance can make a huge difference in a commercial greenhouse. We had a row one summer of plants that were very susceptible to ?? don't even know what it was. They went down more than a month before the others, although they did produce some fruit.
Sick tomato plant mess is pretty gross... I'm always steering toward resistance and away from the dreaded high maintenance varieties.
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Old July 18, 2019   #13
b54red
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Quote:
Originally Posted by nctomatoman View Post
So the best way to consider this is the absolute definition of resistance and tolerance.

Resistance means that the mechanism of the plant resists attack of the agent - in the case of Fusarium, a fungus that moves into the roots from the soil, a F resistant variety means that the roots resist movement of the agent into the roots.

Tolerance means that even though the agent moves into the plants, the plant can tolerate the attack and do reasonably well for a spell after attack.

But here's the thing - the terms are really relative and misinterpreted. In high disease pressure areas, plants won't resist or tolerate the disease indefinitely. For example, let's say you have a Fusarium resistant plant. The plant will resist the disease a bit longer than a non resistant plant, but if the disease pressure is high, it will go down a few weeks later (or some time frame).

So with grafts, if rootstock is highly resistant to this or that disease, in principal it will from some to alot more time. The key then is to use good garden hygiene, keep soil from splashing onto foliage above the graft line, etc - that plant top will be just as susceptible to the disease as an ungrafted plant - the protection is whatever the roots can provide.
Very good definition. I have soil rife with fusarium all three races and even the most resistant varieties can sometimes fall to it. The difference with non resistant varieties is that I can have months and months of good production before fusarium finally makes its presence known rather than plants dying before any fruit reaches maturity. This year for the first time I have even had some of my grafts onto RST-04-106-T root stock give in to fusarium recently. However I had several months of fantastic production from those plants but this year has been unusually hot and dry and I think that has stressed the plants more than a normal spring and summer. Added to the stress on the plants was an unusually early appearance of spider mites which further stressed the plants. Even with all the negatives most of my older plants are still producing tomatoes and continuing to grow as long as I can keep the spider mites under some control.

Bill
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Old July 18, 2019   #14
b54red
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Quote:
Originally Posted by jtjmartin View Post
With grafting in my area it's extra months - not just weeks. I would be growing out of bags if grafting only gave me a week or two.

Jeff
I found several varieties of root stock that gave me months of extra production as far as resistance to fusarium and RKN are concerned but found only one that gave me true resistance to BW along with FFF and RKN.

Bill
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Old July 18, 2019   #15
jhouse
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Boy I have to learn the disease language. I'm assuming the foliar disease I've had is always early blight -- it's possible there have been other issues and not known it. I've not yet had plants die, they do produce while struggling with foliar issues. (none so far this year).

This year I'm just learning a lot -- seeing what works and what doesn't. Learned in a article that some seeds may be disease resistant but just haven't been tested for it, so they can't list them that way. Sounds like some of the disease resistance is more aimed at bacterial rather than fungal maybe?

I'll find a thread about grafting, sounds interesting!
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