Author Topic: Seed sanitation to avoid introducing pathogens: Phytophthora in Tomato  (Read 726 times)

Ocimum

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To avoid diverting the original topic on blight in tomatoes, but continue the very important topic of disease transmission through seed, here a new topic.


Any suggestions on seed-sanitation counter measures that might be appropriate? For example, would freezing kill spores in/on seeds? Would dehydration?

Each species has it's weak points. Freezing beans against the bean weevil is well known.

About Phytophtora in seeds: I do not know what the weak points of the oospores of the species are.

They survive drying in soil
https://onlinelibrary.wiley.com/doi/full/10.1046/j.1365-3059.2000.00515.x

However, they seem to die if the soil containing them reaches more than 40C. Maybe heating is a solution?
https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-3059.1995.tb02719.x
(it does not tell if the soil was dry or wet. Makes a huge difference...)

Lactobacillus may be a way to reduce Phytophthora in tomato seeds
https://www.ijcmas.com/vol-3-1/Jiahui%20Guo,%20et%20al.pdf
I know people who swear about soaking seeds in whey before sowing.

gmuller

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Heat treatment is a method I have seen in books, for general pathogen control, but I haven't used it.
My sous vide machine would probably do the job.
GM

B. Copping

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I was a bit suprised at the half-strength household bleach, and the time period reccomended (compared to what Ive seen in some books); but Im inclined to listen to these pros. :)

https://tgrc.ucdavis.edu/seed_germ.aspx

gmuller

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Interesting. I've always been very cautious with bleach around seed - like, i never use it.
gm

Andrew Barney

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I have used the TGRC treatment method for germinating wild tomato seeds with success. 50% water 50% household bleach. But I have my doubts about the need for it for germinating galapagos species other than as a disease fighting measure.

triffid

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UV-C light may be another method of effective decontamination on small scale. There's also evidence that it increases biotic stress resistance in the resulting plants.

Andrew Barney

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UV-C light may be another method of effective decontamination on small scale. There's also evidence that it increases biotic stress resistance in the resulting plants.

Could you provide some scholarly articles or peer reviewed documents to support this idea? There were a few of us discussing UVC on the homegrown goodness forum for potential mutation breeding.

triffid

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Of course, I should have included references in my first post.

Hormetic UV‐C seed treatments for the control of tomato diseases  https://doi.org/10.1111/ppa.12987

UV Light Inactivation of Human and Plant Pathogens in Unfiltered Surface Irrigation Water   https://aem.asm.org/content/80/3/849

Water is obviously very different than the surface of a seed but considering UV-C has been shown to reduce Phytophthora in turbid mixture, and is employed as a commercial decontamination strategy for fruits and nuts with varying surface properties (https://www.dinies.com/english/uv-seed-disinfector.html) & (https://www.goodfruit.com/uv-light-controls-pathogens/), it would appear to be a promising process worth researching further.

Ocimum

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Plasma may also be a solution, but the price probably not in the reach of many of us, except with contact to universities...
https://www.sciencedirect.com/science/article/pii/S0168160516304664

It removes soem human pathogens, but seed borne diseases were not investigated.

Steve1

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Interesting. Sodium hypochlorite (household bleach) is one of a number of standard sterilization treatments for tissue culturing seeds (generally with a drop of detergent as a wetting agent). Different horses for courses, but 2-5% for 5-30 mins are guides. Standard White King bleach in Oz is 4.2% sodium hypochlorite. Gentle agitation of the seed can be useful to remove air bubbles and ensure sterilization.
I've started a routine surface sterilization of all incoming seeds since I read that over 90% of commercial seed batches of field pea locally (in the late 90's) carried ascochyta fungal pathogen spores. I figure non commercial seed is unlikely to generally be better. 
UV might work, but you'd need to hit all the seed for long enough. Might me a tough ask, especially with small seeds. You could also possibly use it in combination with the bleach, but I'm not sure how much that would increase your sterilzation effectiveness.

If the seed is infected internally - well thats a different ball game.

reed

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I don't try very hard to avoid disease. I'm trying to become more self sufficient it my gardening, developing my own adapted varieties and so on. I'v gardened in the same spot for many years and think especially diseases that can live in the soil are already here. I'm afraid that if I was successful at eliminating disease I would eventually fail and in the mean time my crops might have lost their own resistance. 

Steve1

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Hi Reed,
I understand your position. Eliminating disease is probably impossible. If new diseases come you have to deal with it. But if you import new pathogens / or races it increases the speed of the treadmill we are already on finding R genes and then trying to add them in to our varieties.
Mind you exposing the same vertical R gene to the same pathogen year after year (especially if it's aggressive) over large areas leads to extreme selection pressure and eventual R gene collapse. Wheat rust R genes in Australia have lasted on average ~ 4 years since 1900. Fortunately for wheat there are a lot of R genes to be had across the related wild species.
That is not generally the case for most other crops.