Breeding for Late Blight Resistant Tomatoes

[William Schlegel]

It does seem like there is a lot that goes into the health and productivity of a tomato plant other than the resistances themselves. Extremely short season dwarfs did ok for Julia. As did very vigorous Solanum pimpinellifolium. More than one way to approach problem solving a set of difficult growing conditions.

[Justin Jardinier]

Iron Lady F1 is determinate, so even if it takes LB well, it looks less healthy at the end of the season because of the lack of continuous growth.

Here's what Julia put in that file for Iron Lady F2:

[Nicolas]

In her trial Iron Lady F3 was pretty healthy so it was maybe not LB that plagued the F2

[William Schlegel]

Someone predicted this last year when the F2 was low vigour for me.

[Justin Jardinier]

In her trial Iron Lady F3 was pretty healthy so it was maybe not LB that plagued the F2

Yeah I was curious whether it might not be late blight. She wrote only 'blight' which could be various diseases but it seemed she meant 'late blight', but I wonder if it was surely diagnosed?

Also if she had successful F3, I wonder why went back to F2 instead of using F4....

[William Schlegel]

I can take the blame for that F2 and F3 thing. I grew the seed! All from the same original packet of Iron Lady F1. I grew a few one year, then a few of the F2 and original F1 the next. Saved some seed of both. Shared both with Julia, so she grew both. Did not manage a cross with them which I intended to in order to help with Carol Deppe's original plan.

I am not qualified to speculate on the plant pathology in someone else's garden.

[William Schlegel]

My Crosses with some hope for Late Blight Breeding
MMM x LB PH5 Pimp PI 270443
MMM x Purple Zebra F1
MMM x (MMM x LB Pimp PI 270443) which may make recovering potato leaf blue exserted bicolor and size easier.
(MMM F2 x Purple Zebra F1) x (MMM F2 x PH5 PI 270443 pimpinillifolium)
(MMM x Purple Zebra F1) x (MMM x LA1375)
(MMM x PH5 LB pimp PI 270443 ) x (MMM x LA1375)
Sunviva x MMMF3
(MMM X Purple Zebra) X (MMM x Brad's Atomic Grape)
MMR Dwarf No Blue x (MMM X PH5 LB Pimp PI 270443)
Amethyst Cream x (MMM X Purple Zebra F1)
Galahad F1 x (MMM X Purple Zebra F1)
Utah Heart x (MMM x Sweet Cherriette) - collaboration with Reed whose varieties survive diseases.
Utah Heart x (MMR Dwarf) - collaboration with Reed whose varieties survive diseases.
(MMM x Purple zebra) x (mmm x galapagense x)

Late Blight Clade

• Mission Mountain Morning (MMM) x LB PH5 Pimp
• MMM x Purple Zebra F1
• MMM x LA1375- originally intended for a different disease or diseases but seems relevant here too based on performance in grow out reports of LA1375.
• Dwarf Gloria's Treat x current mix- included LA1375, PH5, and sweet cherriette

I made many more potentially relevant crosses in 2023:
2023 Crosses

• MMM x (MMM x LB Pimp) which may make recovering potato leaf blue exserted bicolor easier.
• (MMM F2 x Purple Zebra F1) x (MMM F2 x PH5 pimpinillifolium)
• (MMM x Purple Zebra F1) x (MMM x LA1375)
• (MMM x PH5 LB pimp) x (MMM x LA1375)
• Sunviva x MMMF3
• (MMM X Purple Zebra) X (MMM x Brad's Atomic Grape)
• MMR Dwarf No Blue x (MMM X PH5 LB Pimp)
• Amethyst Cream x (MMM X Purple Zebra F1)
• Galahad F1 x (MMM X Purple Zebra F1)
• Utah Heart x (MMM x Sweet Cherriette)
• Utah Heart x (MMR Dwarf)
• (MMM x Purple zebra) x (mmm x galapagense x)
• Mr. Stripey x (MMM x Purple Zebra F1)
• Hoosier Rose x (MMM x LA1375)

Just PH5 PI 270443 - NE9 - Seed - Solanum pimpinellifolium L. May be PH5 Source Material

• Mission Mountain Morning (MMM) x LB PH5 Pimp
• Dwarf Gloria's Treat x current mix- included LA1375, PH5, and sweet cherriette
• MMM x (MMM x LB Pimp) which may make recovering potato leaf blue exserted bicolor easier.
• (MMM F2 x Purple Zebra F1) x (MMM F2 x PH5 pimpinillifolium)
• (MMM x PH5 LB pimp) x (MMM x LA1375)
• MMR Dwarf No Blue x (MMM X PH5 LB Pimp)

I harvested a few more crosses since I posted the list I quoted above in September. Everything is now in seed packets for 2023.

Thinking heavily about the PI 270443 potential PH5 source material Solanum pimpinillifolium this morning. Wondering if I should grow it out again and make some more crosses with it.

[Justin Jardinier]

Just PH5 PI 270443 - NE9 - Seed - Solanum pimpinellifolium L. May be PH5 Source Material

Unless there's something I'm missing, based on the PhD dissertation GENETIC CHARACTERIZATION AND MAPPING OF LATE BLIGHT RESISTANCE GENES IN THE WILD TOMATO ACCESSION PI 270443, I think that can be upgraded to certainty.

Also William, what do you reckon would be the wisest course of action - to work on a PH-2+3 population separate from a PH-5 population? Or, combined? I'm thinking that maybe with marker assistance (which would be great), combined could be awesome, but without marker assistance, perhaps separate would be better, since even with heavy disease pressure, it might not be possible to breed homozygosity for all 3 together?

[Roland]

Are there markers for ph5.1 and ph5.2?

[William Schlegel]

These are good questions! I thought the thesis someone shared teo years ago was something like a masters thesis and didn't have the accession number in the title. Hmm now I need to look up this PhD thesis. That PHD project could have potentially found the markers for the two PH5 genes Roland.

Justin I already have started the process of mixing all three resistances in my late blight breeding grex. So I guess I stand by that decision per my advice. However I think it's important that pathogens face variability not uniformity. I think that is part of why small agriculture persisted for deep time and large agriculture looks to have serious sustainability issues.

[Cathy A]

I think it's important that pathogens face variability not uniformity.

I am surprised at the amount of focus on a few selected vertical resistance genes that I see on this site.

I would think the bigger opportunity for amateur breeders is horizontal resistance.

[William Schlegel]

I am surprised at the amount of focus on a few selected vertical resistance genes that I see on this site.

I would think the bigger opportunity for amateur breeders is horizontal resistance.

I have a belt and suspenders model with this bit also a variability model. I don't think in terms of the vertical vs horizontal dichotomy if it even truly exists. All forms of resistance evolved and within the context of natural populations have proven useful enough to persist. So I don't see any reason to exclude one group or the other of resistances. I see tremendous potential in keeping populations non-uniform, introducing as many resistances as possible but at the population level, and in crossing with vigorous robust plants. Two extremely different sources of robustness in my 2023 garden were the Solanum habrochaites accession LA2329 and its hybrids and Reed's old standby tomatoes. I see a lot of value in breeding with both.

Where I think we really get out classed by nature is big uniform fields of food plants without variability. Aka modern agriculture. It leads the mainstream plant breeders to constantly chase better resistance but they've created the need for that by growing genetically uniform crops.

Though on the flipside if an indestructible paste tomato falls of a truck- it probably has been bred to have extremely durable resistance. I don't know if I would breed with it, but I would be tempted. If I found it volunteering in a dry stream bed I might go for it.

[Justin Jardinier]

I am surprised at the amount of focus on a few selected vertical resistance genes that I see on this site.

I would think the bigger opportunity for amateur breeders is horizontal resistance.

My impression is that the only tomatoes we know of that have really good LB resistance, are from PH-2, 3, and 5. And some in habrochaites which I haven't noticed anyone being able to bring to lyc. That's why it's my focus, perhaps same reason for others too. I have heard of 2 people who seem to have some resistance from unknown sources, don't know if that is from the same genes or something else - I wonder if they might have resulted from unknown crosses with some commercial LB resistant varieties with PH genes. For lower LB pressure, weaker different resistance might be useful, like from Stupice, but I think for many of us such weak resistance is not useful.

I read the whole chapter 'Resistance: Vertical and Horizontal' and a bit beyond, from Return To Resistance␁ - Raoul ␁A.␁Robinson. I have to say I was entirely disappointed. To me it seemed he used an awful lot of words to say almost nothing at all, and even gave no actual examples of what he was talking about, let alone examples of horizontal resistance failing, which would be rather crucial - how are we to understand how something works without understanding how it doesn't work? So we really need, or should I say I would need in order to take it seriously, a real life example of it, and an example of a pathology that has overcome such resistance. He gave neither.

Not only that but his logic made no sense to me. He from what I remember created his definition in such a way that if horizontal resistance were ever overcome, even if it took millions of years to do so, then it never was horizonal resistance in the first place. That seems like nonsense to me. And, while he implied that horizontal resistance is basically a defence made up of two or more genes (which in fact would include PH-2 + PH-3 tomatoes!), he seemed to be saying that horizontal resistance can in fact just be from one single gene, which to me makes his whole position self-contradictory and meaningless:

Horizontal resistance is the resistance of the biometricians. Its definitive characteristic is that it does not involve a gene-for-gene relationship. However, its most prominent characteristic is that it is usually, but not invariably, inherited polygenically.

Here's another thing he wrote in that chapter:

Vertical resistance is the resistance of the Mendelians. It is normally qualitative resistance in the sense that it is either present or absent, and there are no intermediates. However, there are a few exceptions to this rule (see Glossary: quantitative vertical resistance). Horizontal resistance is the resistance of the biometricians. It is quantitative resistance in the sense that it can occur at every level between a minimum and a maximum.

Well that applies to PH-2 and PH-3 genes. Simply by their presence or absence, we have, what's that, 12 possible combinations? (Either can be hetero- or homozygous). And the resistance will be a spectrum through those combinations. None of them will have full protection against LB. Seems to perfectly fit his definition of horizontal resistance.

I took his idea seriously without really knowing what it meant, but a discussion some time ago triggered me to read that part of the book, and, well I felt there was nothing to take from it. So I just think in terms of having as much protection as possible. I would love to combine PH-2, 3 and 5; and I would love to have another population with none of those genes but breeding for the same resistance, with tomatoes with some experienced resistance with no name for how they do it, keeping them separate so that their own resistance increases instead of fading away if they get PH genes and rely on them instead. I want separate population so that if the PH genes fail, I still have something else that works, and something less common would be useful since perhaps it will be large scale agriculture where LB will have enough opportunities to work through their defences. So a rarely used defence system is, I would expect, at an advantage in that respect. That's the approach I have settled on for now.

[reed]

with tomatoes with some experienced resistance with no name for how they do it, keeping them separate so that their own resistance increases instead of fading away if they get PH genes and rely on them instead

I guess that is sort of what's going on with my tomatoes, I'll just call it dumb luck for now. That second point never occurred to me, and I certainly don't want that to happen.

It's a bit like how I view things like artificially tinkering with soil chemistry and stuff like that. My garden works as it is. I'm sure it could be better at least in short term, but I think messing with something that I don't completely understand is a bad I idea. If it's not broke, it really is best not to fix it. I have seen a time or two when someone else grew my tomatoes using fertilizer and regular watering, they got bigger yields than I do, but I get plenty for our use without any of that. Making peace with good enough, is a big part of my overall garden philosophy. Maybe a tomato plant is supposed to make ten pounds of tomatoes instead of twenty. Sure, the twenty is doable, if, if, if, but all of those ifs are artificial, and I suspect counterproductive in the long run.   

I'm still going to grow my new PH crossed tomatoes though and see how they turn out. I really want to see what comes from the crosses William did with my tomatoes. My very limited, past experience with PH gene tomatoes was, inconclusive. For most of them I don't know how well they may have done in late season, because early season issues took them out before they had the chance. All the leaves on one called Iron Lady curled up and turned brown very early.  I hope with these new seeds, being 1/2 from genetics used to my garden will fare better.

[Justin Jardinier]

I have seen a time or two when someone else grew my tomatoes using fertilizer and regular watering, they got bigger yields than I do, but I get plenty for our use without any of that. Making peace with good enough, is a big part of my overall garden philosophy. Maybe a tomato plant is supposed to make ten pounds of tomatoes instead of twenty. Sure, the twenty is doable, if, if, if, but all of those ifs are artificial, and I suspect counterproductive in the long run.   

Yes I would guess that perhaps, if one fed tomatoes in that way for enough generations (especially if there was some rate of outcrossing), then the yeilds might be good but they might adapt to need that, and then when that condition is taken away, they might do considerably worse than they did before that process started.

My personal aim is to make neglectable tomatoes. So, even in the first generation before making crosses, when we had a long hot dry spell, and my neighbour was watering their tomatoes every day, I did it maybe once every 10 days. I hope to neglect them more than that in the F2, or at least some of them. Same goes for fertiliser. I don't mind putting some mulch or something like that now and then, but I don't want to do too much work, so, I want to breed them to be as neglectable as possible. Not just for my sake but for others, in fact the main purpose is so that lazy people can grow delicious food. Or not even just about laziness, but general tolerance to changing conditions, and hopefully relative ease of many people growing them in the upcoming global food crisis. In this regard I agree with you - pampering them would be counterproductive. The only ones I consider pampering are hard-to-grow F0 and the F1 is they may be vulnerable. But not from F2 onwards :-)

I'm still going to grow my new PH crossed tomatoes though and see how they turn out.

Yeah sounds cool. If it so happens that your resistance in your other tomatoes has not come somehow from the PH genes, then you might want to keep those ones at a bit of a distance from any with known PH genes, if you don't want them to get those genes too. And if somehow yours did acquire some PH genes, I would guess it might be PH-1, 2, or 3, but not 5 since it seems 5 hasn't been used in commercial tomatoes yet, that I know of anyway, or if so maybe only very recently?

Mixing them all up might also be very good. I would just worry that if the PH-5 resistance is stronger than an unnamed one, the unnamed resistance might have no competitive advantage to stick around. I don't know how justified that thought is - perhaps it would. If it were me I would at least carefully save some seeds for the future so that if they do cross I could always go back to pre-crossed material if necessary, such as if/when PH-5 is overcome.

My very limited, past experience with PH gene tomatoes was, inconclusive. For most of them I don't know how well they may have done in late season, because early season issues took them out before they had the chance. All the leaves on one called Iron Lady curled up and turned brown very early.

That's curious, from what I remember that's PH-2 and PH3 homozygous so should be among the very best LB resistance. But I guess maybe if it did that early, it wasn't LB. I wonder if it was the same issue which Julia had with hers and had assumed was LB?

The LB resistant ones you grow now, were they showing such resistance before you (or neighbours) ever grew commercial LB resistant varieties, or, only after? And from what I remember, one of your LB resistant ones is the one you refer to as 'my Mr. Stripy' - is that different from other people's Mr. Stripy? I seem to remember there may be more than one variety by that name, so I am curious if it is one of those others know about and has the same degree of LB resistance as that, or if it is peculiar to your garden, with increased LB resistance to any of the ones in the community by that name.