Each self-incompatible plant has two (different) s alleles. Each pollen carries one s allele.
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I would love to learn more about the inheritance of SI. Does the above (I added highlight) mean that if we cross an SC with an SI, the F1 will be all SI, due to the SI allele being dominant? And then 75% of F2 being SI, 25% of which would have 2 SI alleles?
If not, then what percentages of SI would we be expecting to find in the F1 and F2?
Thanks!
The self-compatibility (SC) of domestic tomatoes arises from (at least) two broken genes. HT-A and HT-B that may work together in some sort of additive (co-dominant) state. The F1 between SC and SI contains working copies of both genes. https://onlinelibrary.wiley.com/doi/10.1111/tpj.12424
The math gets really fuzzy really quickly, cause to return to a functional self-incompatibility (SI) system, we also need to account for petal size, style length, peduncle length, petal color, etc… A plant self-eliminates if it has a working self-incompatibility system and pale, tiny, closed flowers.
I select for huge flower petals, exerted stigmas, bright colors, and bold flower displays, because I can see them with my own eyes. I don’t need a DNA lab. Those traits provide value in both a SC and SI system.
I love this image which shows the fuzzy nature of tomato genetics… Papers by reductionist splitters show this sort of data as only a black/white line with none of the nuances that actually exist.
Source:
Slice of PLOS: 57 Varieties of Tomato
March 29, 2016 Roli Roberts
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Landraces don’t have to be crossed with wild populations. They do that with tomatoes because they are so inbred.
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I am interested to know how people maintain their seed stock of the self-incompatible tomatoes. How many plants of a given species are needed to keep them viable? Do you rely on hand pollination? I currently have one each of a few self-incompatible species growing and I am concerned with being able to maintain my seed supply for tomato crossing projects in coming years.
I appreciate the input!
Self-incompatible tomatoes cannot pollinate themselves. Therefore, if you grow only one plant, then they probably won’t produce seeds. Except that the various species might cross.
That’s the same situation I observe with tomatillos. People whined to me at farmer’s market that their tomatillo grew great, and flowered profusely, but didn’t make fruit. Someone ignorantly sold them only one plant. Whenever I sold tomatillos, I put 2 or three plants in each pot, so that they have a pollinator.
The minimum population size is 2 plants that aren’t closely related… If they are closely related 2 plants might be insufficient.
I aim for around 20-30 plants in my garden, even if they grow together in a clump.
To really maintain the diversity, population sizes of around 70 plants work well.
I rely on insect pollination. The s-alleles that are most rare have the highest chance of successful pollination, so things tend to balance out, and retain rare genetics.
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I got a packet of LA2329 a SI strain of Solanum habrochaites I think now it was perhaps 2020?. I grew out ten plants the first year and one of the 10 produced seed. So in 2021 I grew out both the saved seed and the remainder of the packet to do a proper grow out. I saved some seed again in 2022 from a smaller growout. I also successfully crossed it with some plants from Joseph’s promiscuous project in 2021 and again in 2022. In 2022 I also crossed it with Joseph’s Big Hill HX-9 and with a cross I made with Big Hill. In 2023 If any LA2329 seed got produced I accidentally mixed it with Promiscuous x LA2329 F2 and F3 seed. I have five clumps of seedlings germinated for 2024 I’ll keep the clumps together and make a row of five clumps. I really hope a bit of back crossing may have occurred by this point but I’ve had no proof of it yet. If its happening eventually some phenotypic variation will show up. I might in a few more years do another large growout of the LA2329 to try to refresh the seed again, but I also have a few other Solanum habrochaites accessions and might switch to working with one of them if I get to a point where I think I’ve done what I can with LA2329 which has some documented potential for arthropod resistance which is really interesting. Tomato seed tends to be long lived so it could be set aside for some years and then come back to. I haven’t gotten a very great seed crop from this particular accession yet but was able to grow enough for my own use for some time. If I were a few zones warmer than 6A I think Solanum habrochaites would be quite a bit easier to work with and produce larger seed crops for me. It seems to always be on the verge of a great seed crop if there were just a few more weeks of growing season. I now have so much F2 and F3 seed of hybrids between it and promiscuous that I’m thinking about attempting to direct seed some. Having some crosses made also takes some pressure off of trying to maintain the original accession.
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