Creating tomato landraces

Adaptation Projects Tomatoes
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People ask me about creating tomato landraces often enough that I want to make a public post…

Domestic tomatoes lack genetic diversity, making them one of the most inbred crops that we grow, and therefore among the most difficult to grow landrace style.

Landrace gardening requires two things:
1- Genetic diversity
2- Promiscuous pollination.

With both of those traits in place, then the crop can undergo survival of the fittest selection for current local conditions.

Domestic tomatoes lack both characteristics. They defied my attempts to turn them into a locally-adapted landrace. I currently believe that purely domestic tomatoes cannot become a landrace.

That motivated me to seek out the traits in wild tomatoes that make them 100% cross-pollinating, which dragged with it a bunch of genetic diversity.

To create a landrace (for example plum) tomato, I would pollinate a few favorite (plum) tomatoes, with a line of self-incompatible tomatoes, and then re-select for the self-incompatible trait, promiscuous flowers, and desired shape/size/color of fruit. The self-incompatible plants donate pollen to the domestic tomatoes. The cross doesn’t work in the other direction. Pooling the pollen from many different pollen donors, (preferably in the neighborhood of 16 to 32) from a self-incompatible population maintained with many parents. And keeping in mind the whole time that promiscuous tomatoes have a many to many breeding system, and best results come from larger populations.

Love,
Joseph Lofthouse
author of Landrace Gardening

flowers-huge-001

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For me, it is a more complicated story, and I am not sure if I can fully tell it in the time I currently have before work. My projects with full domestics mostly starting with Joseph’s cast off technology of Big Hill as sort of a pre-breeding project are bearing fruit and occasionally large numbers of uncontrolled crosses with unknown fathers. That said my five full domestic crossing blocks in 2022 produced four failures and one success in 2022! The one success however, is amazing in that I have a full row of uncontrolled crosses of Mission Mountain Morning X Unknown. I have had similar successes in 2021 with Mission Mountain Sunrise x Unknown. I;ve also had some somewhat similar successes dating back as far as 2017 with other exserted stigma varieties though some of that involved some serious pollen daubing.

I have also been working with Solanum habrochaites accession LA2329 primarily and grown out a number of generations of the Lofthouse promiscuous project since 2018. I have quite a few plants now in 2023 of Promiscuous x LA2329 both F1 and F2 plants so 9/16ths Solanum Solanum habrochaites and 1/16th Solanum pennellii. I also have a few plants of Big Hill x LA2329 and MMM x LA2329 both in the F1. There are a number of difficulties involved when working with these wild species crosses- mostly which relate to viability and reproductive difficulties. Weak F1 seedlings, F2 plants that cannot reproduce or only with great difficulty, and poor viability of F1 cross seed to name a few. These difficulties do give me some pause on occasion.

One upside is that many of these hybrid interspecies populations should have a mixed breeding system- any plants with the obligate outcrossing system intact should still be using it. I suspect I have such a system in my own garden.

One thing I am very curious about is the possibility of using Solanum habrochaites as the mother by back crossing repeatedly with the hybrids. Joseph is much farther along on this having finally recovered some with desirable traits. However, I am curious to try a larger grow out of my strain of LA2329 as it has been repeatedly exposed to hybrids for generations now and see if any of it shows signs of that type of crossing.

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A good first step with purely domestic tomatoes would be to cull any with closed flowers, and to stop trying to keep them pure, even to, gasp, encourage cross-pollination.

Big Hill, descends from a classic beefsteak with open anther cones. Some of the cherry tomatoes have exerted stigmas. Growing those sorts of beefsteaks and cherries close together would help the domestic tomatoes.

Tomatoes exist on a spectrum from fully inbreeding to fully out-crossing. Moving the population somewhat away from fully inbreeding would help them. Introducing some wild genetics would help, especially if the population as a whole retained the beefsteak/cherry type flowers ability for occasional out-crossing, even if mostly self-pollinating.

More and more, I embrace the mixed breeding system.

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I have at this very moment some cherry tomatoes (mix up of crossed pimps) and some of my Hoosier Rose (beefsteak type) that are exhibiting open flowers and exerted stigmas. Various bees are busy doing their thing so a cross might occur on its own.

Still, if I wanted to make sure one happened could I just transfer some pollen? Or even though the flower is open is it still necessary to emasculate the one receiving pollen? Seems like the stigma still has to grow out past the anthers so is it most likely already pollinated by the time it protrudes?

I am not good at all at hand pollinating tomatoes, but the Hoosier Rose is potato leaf which I’ve learned is recessive. If I could pull off pollinating one with the regular leaf cherry, I could then start all of the seeds from that one fruit and easily discover the actual crosses. At least that’s what I’m thinking. Or any other of my regular leaf types would work too.

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Reed, if you just daub pollen from a regular leaf plant on the exposed stigmas of Hoosier Rose, you should get a mix of potato leaf and regular leaf seedlings. The regular leaf seedlings will be F1 hybrids.

I use a pollinator tool and a pollen spoon that came with a different pollinator tool to collect the pollen.

This fellow in Norway is doing the same thing except he picks off the anthers and uses an old sunglass lens to collect the pollen.

I definitely find that not picking off the anthers (emasculating) works but that there is a mix of seedlings. With certain strains I got no crosses even then, but the ones that had exserted stigmas that stuck out more the crosses worked. It definitely worked better when I was new to tomato crossing and in the open field where sometimes the flowers dry up when emasculated.

It also works better if not emasculating if you still pick a younger flower that maybe is not emitting pollen yet. That way your selected pollen gets a head start. Daubing the same flower three days in a row can help as well starting with a young flower.

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I’m just no good at the dissection thing, I’ve tried it several times with zero success. But right now, I have the Hooser Rose flowers which are not especially exerted but are very open. And I have the cherry (pimp crossed) flowers, lots of them. So, I’m going to pick out a couple very fresh HR flowers and just pick cherry flowers, open them up and dab on the HR flowers. I’m not good a collecting pollen either and there are lots of flowers.

That might solve all of my problems of space and everything. I’ll just dab lots of cherry flowers on an HR flower and next spring plant ALL of those seeds in a big tray. Any crosses will show up as regular leaf and I’ll be on the way to my first on purpose tomato cross.

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Domestic tomatoes as a species approximate the genetic diversity of a clone. 95% of their genetic diversity was lost during domestication and from the heirloom inbreeding purity mania.

One study found more genetic diversity in a single sample of one wild tomato than in all the domestic tomatoes in the study combined.

I do not advocate the idea that a landrace can only exist as a mix of wild and domestic species. (Or that landraces can only be wild varieties). Except in the case of tomatoes, I would say that domestic tomatoes are too inbred to meet the genetic diversity criteria of being a landrace.

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My intuition is to try the cross the other way around. Wouldn’t nature do it by collecting pollen from the open flowers and then pollinating the exserted stigmas? If your cherry tomatoes aren’t exserted then it might not be worth the effort and would be easier to start with some that have exsertion.

Unless I’m missing something the potato leaf/regular leaf thing would only be useful if a single cross is desired and useless in the long term Landrace style of breeding. After you make the first cross your marker disappears.

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I found it fascinating in one of Casey Piscura’s videos he said that when they do the frost trials on the tomatoes they find a lot of natural crosses. He said he thinks hybridizing makes the plants more frost tolerant. Maybe someone can use this information to move the needle toward more naturally outcrossing domestics.

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I agree that does sound more like what might happen naturally but also, I think more likely to fail if I try it on purpose. Plus keeping track of a single individual little flower and fruit seems like a pain in the rear. I’d probably lose it, or accidentally eat it, or kill it trying to put a tag on it.

Some of the cherry flowers are very exerted but I suspect they are often already pollinated by the time the stigma is exposed and even though it is exerted the cone is tightly closed which I think makes it harder for me to make the cross. The HR flowers are not really exerted but are very open so I figure it will be easy to just dab on some pollen.

The tell-tell of regular leaf plant showing up from potato leaf seeds is what I’m after. I don’t care all that much about the landrace aspect, I’ve just never been successful at a purposeful tomato cross and think it would be fun. This is the best way I’ve learned of to confirm it, assuming it works.

Actually, though my cherry tomatoes already are a landrace of sorts. The mixed-up result of a random cross that showed up several years ago. Also, I suspect that crosses may happen fairly often as I commonly see open flowers and exerted stigmas and I often see a number of different pollinators taking advantage of that. I rarely find one though because I only grow enough tomatoes for us to eat fresh and can as sauces, and juice.

On your post about the frost tolerance, the Hooser Rose plants that are blooming right now are volunteers that survived a light frost. There was about ten of them but the light frost and some kind of tiny snail killed all but three and those three look great. I’m making a point to save lots of seeds and also from an anomalous cherry plant, in case the tomato gurus might want them.

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26 posts were split to a new topic: Tomato Self Incompatibility and Crossing with Wild Species

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I’m growing some rather small tomatoes that have wild genetics, and some way smaller pimps, that are exserted before the flower even opens, which is nice. Some of the crossing I tried with some such pimps I just pollinated before the male parts were active, but without emasculating them. I’ll see soon if they were successful I guess. Hopefullly that level of exsertion will come through with the crosses, by F2 stage or so I’d like to be able to stop manual crossing. Working with some nicely exserted Galapagos varieties too. And now growing out what should be arcanum crosses, harvested the cross fruits like a week ago, so hoping they’ll have exsertion too though if they’re successful, might be a few generations until they’re tasting good. Seems I might have got a peruvianum cross too but we’ll see soon if it really was. High hopes for exsertion in the coming generation.

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Some of my exserted strains stick out their stigma before releasing pollen.

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I realized this weekend I have attempted over eighty unique hand crosses in the last month or so since I have had flowers to work with. Not all will take. However, I suspect that as many or more than I made last year have already taken for sure. From most of those I will recover seeds.

My unique to my garden tomato population is diversifying. However, with most of these crosses because I crossed early and often, the population is moving away from exserted stigmas. There are a few key crosses that preserve, maybe even improve, that trait though! Such as Exserted Tiger x Exserted Orange, Exserted Orange x MMM, and Exserted Tiger x MMM.

Most of my 2022 crosses with Solanum habrochaites LA2329 and F1 and F2 hybrids are still in the future though they have finally begun- at least with the F1’s. That is currently where any obligate outcrossing traits would be most likely to come into the population. Though some may be in some of the Lofthouse promiscuous project I am growing out broadly. Hard to know for sure. R18 certainly had good flowers and I am growing it again!

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This flower is from the original R-18. Compared to a domestic tomato flower.

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I can’t remember what generation of R18 I am on, this has to be at least generation two to grow in my garden. Maybe three. Anyway, it has held up well so far on the flower size front. Pity in some ways it hasn’t shown signs of outcrossing to other strains either. Will see what it does this time.

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I cloned R-18 the first fall, and used it the second year as a pollen donor and mother, making manual crosses, with varieties that I think fully express self-incompatibility. This spring, I planted out a large population, spacing them 6 feet apart, so that I can really focus on the traits of each plant.

This spring I also planted out the F2 population of crosses using the (purported) SI population as pollen donors to Solanum pimpinelifolium, and SunSugar. I selected in the F1 for good flavors, and exserted stigmas. That makes the population a 4 species clade. I intend to select this year for plants that act self-incompatible, and have suitable flower types.

I planted a population which I believe contains habrochaites cytoplasm, and more than 75% habrochaites DNA. along with larger yellow fruits with 3 locules. This descends from years of growing habrochaites near to the inter-species crosses, and selecting among the offspring for fruits with three locules and a yellowish tinge, and slightly off-type leaves or stems.

I only grew one domestic tomato variety. Growing a seed crop for Experimental Farm Network for the variety “Yellow Chariot” which was developed on my farm. It is potato-leaved only. I don’t know how that happened…

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Why would that have that effect? For example, if I cross early and often but specifically chose exserted individuals to cross with as both parents, why would that not have the opposite effect? I can’t see why doing them early and often would make them move away from insertion.

This year, so far I’ve harvested the seeds of 16 different (apparently) successful crosses. It felt like a lot to me, until reading your 80 in one month! :open_mouth: Mind you, some of them took many crosses to get one with seeds. And I won’t have the space to grow out all of these in large F2 populations, but, I think they will likely all come in handy down the road somehow :slight_smile:

Now that I’m crossing outside, I really appreciate the lack of wind inside! My plot is really quite windy. Makes it tricky for some of my refrigerated pollen which is in very short supply!

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These are mainly domestic x domestic crosses. The exserted condition is in my experience, exceedingly rare amongst varieties. So if I make a exserted x inserted cross I can recover that in the F2 with a large grow out. Then stabilize in the F3. Use more broadly in the F4. If I cross again in the F1 which I just did, with less selection in the F2 last year, my overall population is drifting away from exserted with some of these new crosses now only 12.5% Big Hill and fewer years of selection in between. Only a small percentage of my 80 new crosses are with well selected material for exsertion. Crosses like Exserted Orange x Exserted Tiger and MMM F3 from the best exserted F2 x Exserted Orange.

I can reverse that trend away from exsertion by selecting for exsertion and by growing larger numbers of the exserted x exserted crosses. If I make a grex for instance, weighting it heavily with exserted x exserted.

12.5% may be enough in some cases to find rare individuals with the trait in the F2. In other instances I may need to back cross. I’ve already made a few of those and one reason for that is to make recovering everything I like, including exsertion, easier.

A safe domestic grex might be possible by using only original varieties with exsertion but that would limit my original variety choices within my collection to Big Hill, Exserted Orange, Blue Ambrosia, Golden Tressette, an exserted pimpinillifolium Andrew sent me, Exserted Tiger, Mandarin Mini, an unknown exserted potato leaf, and the best exserted of Mission Mountain Morning. Also maybe a few others within domestic. Then only using exserted populations of certain wild species.

Further all exsertion does not seem to be created equal and some comes out to play only with the right environmental cues. So some of mine has proven a little elusive in subsequent years after a year of tremendous success with Mission Mountain Sunrise in 2021 I had a year of much less success with the descendants of the best exserted individual in 2022. So I went from wondering if the cross with Big Hill HX-9 to Mission Mountain Sunrise that led to Mission Mountain Morning was necessary to thinking it was completely necessary.

I’ve also found the trait(s) involved annoyingly elusive in the promiscuous project. The One! Was originally a 2021 selection for extreme exsertion and a very open anther cone that just happened to have amazing flavor. Flavor varied in 2022 but the flower was generally dissappointing compared to the 2021 original.

An important note though. The entire garden, does not need to have exsertion. The occasional individual will lead to crosses in my experience. Selecting for natural crosses also naturally selects for occasional individuals that support that with exserted blossoms.

I have a row this year of MMM best exserted x unknown fathers and I think there must be at least two fathers so far based on some having extremely blue fruit and some very green. Most flowers are similar huge messy beef steak types. Not terrible for outcrossing potential. It would not surprise me if something like Exserted Orange was amongst those fathers. Though I haven’t seen an individual with what I would term “best exsertion” yet in that F1 mix.

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Also 16 is a lot! Last year was my biggest year ever for crosses until this year and it was about twelve crosses. 80 is completely unmanageable to keep all as separate discrete entities. Thus I will probably do some combining!