Blight Resistance in Potatoes and Tomatoes

[Diane Whitehead]

Yes, I deleted my snarky comment about hiding a few seeds in a Kleenex, but obviously you had already seen it.

I  re-read all the relevant parts of The Tao of Vegetable Gardening and have just checked out the list of genes on  https://tgrc.ucdavis.edu/index.aspx. I thought some more resistance genes might have been discovered  since your book was published.  You wrote about Ph, Ph-2, Ph-3.  They also list Phf,  Phytophthora infestans field resistance, incompletely dominant, and found in the cultivar Atom.  I don't know whether that is a new one, or just not very useful so ignored by breeders.

I looked up Atom on Tatiana's list -  SSE TOMATO 782. PI 283906 (Czechoslovakia).  added later: This might not be the same plant.  Prairie Garden Seeds lists this Atom: an early, productive, small fruited, bland tasting, light red tomato from the Central Experimental Farm in Ottawa.

I looked at all the genes to see if any inspired me to breed with them.  Most were negative, but how about the one for shiny leaves?  Maybe those blight spores would slide right off.

[Doro]

I think shiny leaves are a good idea.
My area usually has frost before blight arrives, but the few times I got (European) blight - the wooly tomato varieties all got (badly) affected. The ones with less hair survived a lot better.
Leaf shape also seems to play some role. Carrot leaf did slightly better than potato leaf or regular leaf... which makes sense in terms of exposed leaf surface area I guess.
I didn't grow real shiny leaf varieties yet, they are hard to find here, but the easier the plants dry off, the longer they survive a blight attack.
Growing tomatoes in a greenhouse or under a roof does not really stop European blight unfortunately. A greenhouse just buys a week or two if you can keep the air humidity low inside.

[Diane Whitehead]

I've just been checking on sources for late blight resistant hybrids.

I've never bought hybrid tomato seeds before, and I'm appalled at the prices! 

Oh well, what else do I spend money on except books and seeds.

[nathanp]

I've just been checking on sources for late blight resistant hybrids.

I've never bought hybrid tomato seeds before, and I'm appalled at the prices! 

Oh well, what else do I spend money on except books and seeds.

Diane, I have purchased hybrid tomato seeds, but mainly to use in dehybridizing something useful from them.  But I would steer clear of anything that is protected by law.

Regarding the Pf genes you mentioned earlier, what I am seeing for those look like the sources are from older tomato varieties, prior to the modern Ph1 through Ph5 genes were isolated.  I could be wrong, but I would question whether they are anything useful. 

[William S.]

It sounds like for now Skykomish and Iron Lady are good breeding stock until the PH5 lines are released.

Sounds like Skykomish is pretty long season though I bet it tastes good.

So how about this as a strategy. I've been looking for ultra short season tomatoes. Shortest season so far is "sweet cherriette" I want that attribute. So Carol says I have perhaps 5-10 years to work before things get obnoxious for my blight intolerant friends. So what if I make a series of hybrids with my favorites and "Iron Lady" then grow out the F1, properly dry and freeze the seed of the F1's so that the F2 seed of the project is ready to go when the multi strain blight hits my area. Do the same with the PH5 strain of tomato when available. Sort of a late blight insurance policy but without the risk of selecting the late blight resistance back out before I need it.

Alternatively send some of the F2 to be grown out by someone already heavily impacted with heavy late blight pressure in the hopes they will return some seed from the best plants.

I probaby have a lot of potential unknown resistance in the wild material I am working with along with Joseph and Andrew but it might be nice to have a freezer packet full of something with known resistances as well. Shouldn't take much garden space to get that packet of F2 seed.

[William S.]

My beautifully promiscuous tomato project, was started in direct response to Carol's warning about late Blight. The basic idea behind growing self-incompatible tomatoes, is that every seed will be a unique F1 hybrid in every generation. The hybrids are self-generating, and self-perpetuating, so it will be a trivial matter to throw hundreds of thousands of genetically unique varieties at the late blight problem. There are all kinds of paths the genome might take in the race against last blight. I'm still 2-3 years away from releasing a somewhat stable self-incompatible variety in something larger than a cherry tomato. I'm expecting to start the late-blight trials this summer.

Now that I understand self-incompatibility better, I have adopted the ancient practice, of allowing the wild species to grow along the edge of the field, because the domestic varieties are strengthened by having the wild relatives growing nearby.
.

Joseph, how do you plan to do the Late Blight trials? Do you have a late blight problem nearby or a collaborator far away?

I've thought the wild material might be enough but also think it might be good to get a few hybrids of my favorites with "Iron Lady" wouldn't take much garden space to have one Iron Lady plant around.

[William S.]

Skykomish x Big Hill should produce bicolor F1 plants with one copy each of PH2 and PH3. The F2 would hopefully segregate for the important Big Hill characteristics of short seasonality and open flowers. Would need late blight or gene testing to get plants back with the resistance.

[Joseph Lofthouse]

Any disease trials done with my tomatoes will need to be done by collaborators in other places, because tomato diseases are super-rare in my garden, and I'm not willing to introduce some, just for the sake of science.

Hmmm. Wondering about sending a couple of populations of the wild species to be screened for blight tolerance.

[William S.]

Any disease trials done with my tomatoes will need to be done by collaborators in other places, because tomato diseases are super-rare in my garden, and I'm not willing to introduce some, just for the sake of science.

Hmmm. Wondering about sending a couple of populations of the wild species to be screened for blight tolerance.

That would be informative.

[William S.]

http://jandlgardens.com/xencart/index.php?main_page=product_info&cPath=100&products_id=577

Some of our now shared habrochaites grex "neandertomato" comes from LA 1777 in his notes on "Wild Child" Lee Goodwin at J and L gardens has it as a source of blight resistance.

[nathanp]

Skykomish x Big Hill should produce bicolor F1 plants with one copy each of PH2 and PH3. The F2 would hopefully segregate for the important Big Hill characteristics of short seasonality and open flowers. Would need late blight or gene testing to get plants back with the resistance.

Yes. I think the way the math works is F1 plants would all each have one copy of Ph2 and Ph3.  However crossing F1 to other F1 plants would start to segregate for both Ph2 and Ph3.  25% would have two copies of Ph2, and 25% would have two copies of Ph3.  Only about 6.25% (1/16th) would have two copies of both Ph2 and Ph3, which is what you ideally want to have since two copies provides substantially better resistance than a single copy of each.  If you are factoring in other traits such as short season growth and open flowers, you could be looking at much lower percentages.  If the traits for short season and open flowers segregate similarly, you might need several hundred of the F2 plants to be grown out and evaluated. 

[Joseph Lofthouse]

I have been working on a beautifully promiscuous self-incompatible tomato project. The end goal is a population of tomatoes that automatically create a new F1 hybrid in every seed, so that we can easily and inexpensively throw hundred of thousand of genetically unique plants at problems like late blight.

Today, I received a grow report regarding this project.

"This was the worst year in my lifetime for growing tomatoes in PA. It was the wettest year in recorded history -- 25+ inches above normal rainfall. Blight and more blight. I do not spray for this and grow organic. Everything died except S peruvianum, S habrochaites, and the interspecies crosses. I am returning these offspring...."

Yay!!! It looks like this project holds some promise for dealing with blights. 

[William S.]

Intriguing! I think I will strike Iron lady and Skykomish from my wish list.
 

[William S.]

 There is a potato variety named defender and another named elba both of which have blight resistance. Wondering how hard it would be to grow some TPS from them.

(Edited to remove error)

[nathanp]

William S - I think you mean potato, not tomato.

If you mean Defender, that has a single R gene (R1).  At best it has medium resistance which can be overcome.   I would need to look up Elba, as it is a European potato and may not be available in the US.  There are better ones out there for breeding with, especially if you want to look outside the pool of cultivated potatoes.  What you ideally want is durable field resistance, meaning the plant is not affected.  There are very few potatoes with what is considered durable field resistance, but there are a few available to potato breeders through the USDA genebank.  One of the problems with breeding tetraploid potatoes is that most potatoes descended from them will segregate for the genes present in the parents.  Achieving homozygosity in tetraploids is difficult and may take many years and thousands of plants, potentially.

This article has a brief summary history of available R genes for LB resistance, and where efforts are heading with breeding work, and why potatoes with single R genes, or sometimes multiple R genes are overcome.  I would recommend downloading the PDF.
https://www.sciencedirect.com/science/article/pii/S1876610212003049

Regarding multiple gene potatoes, the following article (again, download the pdf) explains some of the details and surprisingly, discusses that there are other factors in play other than just R genes. 
https://www.researchgate.net/publication/296623252_The_Adoption_of_Cv_Igorota_in_the_Philippines_and_Vietnam
There is a chart that compares several potatoes including Igorota and Favorita.  Igorota, grown in the Phillipines, has near durable field resistance, while Favorita is susceptible, but they share the same two R genes, so there obviously are other genes at work providing resistance that are not identified.  Cooperation88 is a CIP bred potato that so far has provided durable field resistance in China, and has at least 4 major R genes.  The same two as Igorota, plus two others.  Igorota and Cooperation88 are from similar LB breeding populations. 

There are also potato lines that have resistance to LB, but no known R genes.  Those are the ones that interest me the most at this point.

I'll post in more detail later after I compile some of my notes.