I’m going to write a lot. If it’s too much for you to read, my main question is under ‘2’ in this first section.
I’ve been trying to understand something about your SI tomatoes. I understand now (don’t know why it took me so long) that the aim is no merely that they can’t pollinate themselves, but also that they cannot be pollinated by domestic tomatoes. As you’ve said elsewhere about the SI lines you’ve bred, “Pollen flows only from the self-incompatible population to the self-compatible population”.
So I would love some clarity on 2 things, if possible.
1 - I’m guessing that if one adopts an SI system from a wild population into a domesticated line, then if it becomes fully SI, it should still be compatible with the wild species, or at least that wild accession, that the SI system was adopted from. Does that sound right, and is it true in your case?
(Also I’m guessing that, for example, if one adopted a habrochaites SI system into a domestic line, it could still receive pennelli pollen, and if a peruvianum complex SI system, then potentially also could receive pennellii pollen).
2 - For your SI tomatoes, e.g. your ‘elites’, what is the practical result? I understand they can’t pollinate themselves, but what results have you (or others) been getting in practice when you try pollinating them with:
a) pure domestics
b) SC wildings, Q-series, or SC individuals of any of your other lines
That’s what I’ve been wanting to know. Now I’ll just say what has given me renewed appreciation for this project…
I love the idea of increased genetic diversity. And I love the idea of extreme interbreeding for the initiation of a landrace project, so that the population can rapidly adapt to a new region. But in my mind, I had been thinking merely having exserted stigmas would be a good way of having a high enough crossing rate to aim for the traditional landrace method. It seems to me that traditional landraces, of many crops at least, have just enough outcrossing to maintain a relatively consistent phenotype whilst still having the capacity to adapt ‘enough’ over time. This seems appropriate for a population that is already mostly adapted to a specific area, and seems to work great for those traditional landraces, which have been rooted in their land for centuries or millennia.
So it made sense to me that we adapt that method with our ‘modern landrace’ approach by starting with hybrid swarms and a higher rate of crossing, but over time settle into that traditional landrace way with a lower but significant enough rate of crossing, and saving seeds from the group, specifically avoiding the modern ‘purity’ attitude.
But when it comes to tomatoes, I realised that… or at least speculate that, merely having exserted stigma and a diverse starting population, would likely not be sustainable in the medium or long term. (I’m thinking medium term as a few decades.) Because, the higher susceptibility to cross would in most cases mean crossing with neighbours’ tomatoes. And that would mean inheriting all of the problems they have that we have been trying to avoid - inserted stigmas, small flowers, and lack of genetic diversity. So over time ours should also loose their exsertion, and have their genetics diluted back to the general low level of diversity.
This might be saved somewhat by the tendency for modern tomatoes to also include some wild genetics. But our diversity would, in the long run, be limited by the global, or more specifically our neighbourhood’s, level of genetic diversity. As if we brought a fine Scottish single malt whiskey to a barbecue and let it be added to the punch.
And it’s for this reason that I now understand the importance of making an SI population. Not just to make the population diverse and outcrossing, the individuals unable to self pollinate. But rather, to protect them from the world’s domestic tomatoes, by making them unable to be pollinated by them. To me this seems far better than a merely exserted population. It seems like a far far more sustainable way.
One more note…
If this isolation is a key aim, not just the the 100% outcrossing trait, then, I’m thinking that it could also be beneficial to develop multiple domesticated lines using different SI systems. That way, they would not only be isolated from the world’s domestic tomatoes, but also from each other. So gardeners could grow multiple tomato crops, all 100% outcrossing, but still maintain distinct varieties!
For example, imagine if there were 10 varieties using peruvianum’s SI system; 10 using habrochaites; and 10 using chilense. Potentially people could choose 3 varieties from those, one from each group suited to their region and needs, all different, and all easily maintained as distinct lines even if planted right next to each other. And all 100% outcrossers.
And of course no need to stop there. There are at least 7 SI systems available right? And no limit to how many varieties people could develop within each SI system.
Now I know it’s been a huge amount of work just to make your SI tomatoes. But with group effort, I assume that extending this to multiple SI systems is a possibility. Yesterday, I started one attempt - I have a bunch of peruvianum accessions, a few chilense accession, and a couple of corneliomulleri accessions. Here’s the crossing chart I’ve been using for reference, with some of my notes added:
Unfortunately it doesn’t separate the peruvianum complex into the individual species. So, I don’t know which species are compatible. But anyway, I used an SC pennelli accession to pollinate all the peruvianum and chilense accessions I have currently flowering, attempting to using pennellii as a bridge to bring the peruvianum and chilense genetics into a domesticated population. I chose an SC pennellii aiming to avoid clashes with pennellii SI system. [Edit: I just realised chilense is not included in peruvianum complex, I forgot that. But anyway some of my supposed chilense accessions have clearly bent anther cones and I read chilense is meant to always have straight anther cones, so I have doubts that they might in fact be peruvianum, and that’s why I’ve been trying various crosses with them too. I also tried mentor grafts with them but all failed so far).
I’m lacking space so I have only 1 plant of each accession growing inside, though I have 1 or 2 of several accessions also growing outside, which I will try also once they flower. Next time I should try this on a larger scale but who knows, perhaps this will enable me to start… My hope is that I could either make a pennellii-crossed SI population (or maybe 2 if the chilense and peruvianum each make their own), then cross them to domestics and bring over the SI system, or maybe even cross the F1s directly with domestics and work on getting that double-crossed population SI.
Now, not merely for me but for the community in general, I think it could be really good to have some kind of road map for good methods for making an SI population. A method that increases efficiency of time, reducing the years it would take.
For example, I’m thinking perhaps in the F2 generation, we should
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cover some flowers of each individual with little bags, vibrate the flowers, and check if any seedy fruits form? Perhaps this is an efficient way of telling if the plant is SC or not? They pass if no fruits or at least no seeds form.
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Perhaps a second check could be to emasculate some flowers of each plant and use domestic pollen. To pass this test they need to not give fruit, or at least none with seeds.
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Emasculate some flowers and pollinate with pollen from individuals that pass steps 1 and 2. They pass if seeded fruit forms. (Presumably ideally need to use multiple pollen donors for this to be sure? It would… depend on which part of the SI system the SI donor holds, right? So failing from one donor doesn’t necessarily mean failure?)
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Use their pollen to pollinate known fertile individuals - I’m guessing that it would not matter whether the females are SI from the same population or even SC domestics. They pass this pollen fertility test if seeded fruits form.
If they pass all 4 tests, they should be fertile SI individuals.
Step 3 is tricky since one has to know which females are SI, and one would not know this yet in the F2 generation. One could do it in the F3 generation once one knows, or over Winter indoors or just later in the season, once one has worked it out. Or, one could do many tests, keep records, and work it out at the end of the season knowing in retrospect, which would mean more work but cutting down the work by months or even a whole year, depending on ones growing system.
I wonder if this seems a wise approach. And I’m also wondering whether it’s best to work on the SI system and the SI peruvianum/chilense X SC pennellii stage; or at the domestic X [SI peruvianum/chilense X SC pennellii] stage.
If the former, it would have to be worked on again at the latter stage. But… there may be some advantage of working at both stages - it would be good to know whether it would be more efficient to work both or just the latter stage. And I’m guessing if only the latter, that would probably work better the larger the population one is working with. Probably hard to know which would be the best approach without trying, but perhaps you guys who have been working on the SI domesticated lines have insight into this.
That would give rise to a similar question for other systems, for example working on it at:
lycopersicum X SI pennellii stage; or at the lycopersicum X [lycopersicum X SI pennellii] (or [lycopersicum X SI pennellii*] X lycopersicum) stage.
And that would be same for other crosses of SC edibles direct with SI wilds, such as lyc with habrochaites. And just to throw in some fun, we don’t even need lycopersicum involved at all if we don’t want to. We could make a domesticated SI line just out of galapagense, cheesmaniae, or pimpinellifolium; with SI pennellii or habrochaites! Or a mix of sweet SI peruvianum with SC pennellii and exserted accessions of galapagense, cheesmaniae and pimpinellifolium could be quite an exciting mix!
