Here is my latest experimental farming post, about my experience with different Brassica species that led me to Ethiopian kale, plus the history of domestication of the genus through polyploid hybrids, and thoughts about taking that process further.
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Very interesting! Brassica oleracea is my favorite vegetable (especially the flowers and stems), so Iām deeply interested in the species.
In zone 7, being able to overwinter Brassica oleracea without protection isnāt quite a given, but many varieties will make it. With a little bit of protection, I think most would. In fall of 2022, I went into the winter with eleven kohlrabis and five Brussels sprouts plants. I ultimately got seeds from three kohlrabis and three Brussels sprouts; the rest died. The Brussels sprouts plants were all unprotected, and half the kohlrabis were. Sadly, the only kohlrabis that survived were under a hoop house, so those are clearly less winter hardy. (I was pretty sure they would be, hence winter protecting half of them, just in case.)
I let them cross if they wanted to, and Iām going to plant the seeds. Iāll be happy with anything tasty I get, and Iād be delighted if the kohlrabi x brussels sprouts cross gives me descendants that are that are more cold hardy and have big thick juicy stems.
Iām also planning to try a lot of rapa, napus, and juncea varieties, all of which are supposed to be more cold hardy in general as species. I prefer oleracea in general, but I suspect I can get some very tasty stuff out of those species, perhaps more easily. Iāll see what happens next spring. And if they make some interspecies crosses here and there, sure, why not? Works for me!
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Brassicas are mostly self pollinating so if you want to do a wide cross (and not have to grow out thousands of seeds looking for hybrids) then hand pollinating to produce a small amount of hybrid seed seems to be the better strategy (provided you have decent eyesight and a steady hand, since those flowers are fairly tiny).
I wonder if anyone on the forum has other local wild brassica species on hand that they could try hand crossing with cultivated forms. If humanity could create so much from just three original species imagine the untapped possibilities.
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That seems to be the consensus that the original diploid species are outcrossers. Not sure why the references I found were saying otherwise. The tetraploid hybrid species seem to tend toward selfing instead. Not sure if I should update the article. The group is definitely a highly malleable genus. Iām hopeful this article inspires more people to consider interspecies crosses to create new species. That definitely is my plan for the future.
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I have a wild Brassiceae, hoary cress, but itās not winter hardy or summer hardy ā itās just a spring plant. Itās small, and it sprouts in mid spring and goes to seed by late spring, while itās fairly warm and thereās water in our ecosystem. Itās great for foraging, but I donāt think thereās anything special that makes it worth crossing into my domesticated plants. Iām content to sprinkle its seeds around and eat anything that shows up.
Iām not actively looking to do interspecies crosses within the Brassica genus, since I think I can get everything I want with the existing species, but Iām happy to let the plants cross themselves if they feel like it. Iāll interplant them, save seeds from the best every year, and replant. I probably eventually wonāt even bother to keep track of which seeds come from which species, and will just keep them all in one jumbled population.
Iād like to see more tastiness in the middle of midsummer, more drought tolerance in midsummer, and fresh flowerbuds that taste good (broccoli) all year round, so Iāll keep an eye open for anything with those traits.
Hi Shane! Nice to see you here 
Youāve already read this but for the sake of others Iāll share this here too, just to clarify itās not merely the trait of outcrossing thatās happening here, but self incompatibility, which I think may be a bit of a stricter meaning, i.e. not only that they tend to outcross, but that they canāt self pollinate.
From āPlant Mating Systems: Self-Incompatibility and Evolutionary Transitions to Self-Fertility in the Mustard familyā:
Here, the focus is on the molecular genetic analysis of SI and mating system transitions in the mustard (Brassicaceae) family. This family includes self-incompatible obligate outcrossers, such as the economically important Brasssica oleracea and B. rapa crop species and wild Arabidopsis lyrata and A. halleri, as well as predominantly selfing species, such as the model plant Arabidopsis thaliana.
From āAgronomic Improvement in Oilseed Brassicasā:
Brassica rapa is primarily a self-incompatible species, as are the other diploid brassicas, although some types of B. rapa, e.g., yellow sarson, are self-compatible. The self-incompatibility (SI) in cruciferous species is of the homomorphic sporophytic type determined by a single S locus. About 50ā60 alleles are known at the S locus in B. oleracea (Nasrallah and Nasrallah, 1989). The allelic interactions at the S locus are dominant, codominant, or recessive depending on the alleles involved. This system ensures that B. rapa is normally 100% outbreeding and consequently breeding methodologies for this species are designed to take advantage of this natural heterozygosity.
The amphidiploids, B. napus, B. juncea, and B. carinata, are normally self-compatible species, though S alleles from B. rapa have been introduced into some genotypes of B. napus in order to develop SI-based F1 hybrids. Such hybrids have recently been registered for commercial production in Canada.
Iād love to know about B. Nipposinica, B. Pekinensis - if anyone knows if they are SC or SI, please share and tag me!
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While as you note, this isnāt ānewā information, you just made it click for me. I had some rapini (b. Rapa) go to seed this spring, along with a couple Chinese-type broccolis (b. Oleracea) and a tiny bok choy (also b. Rapa) that bolted without even making a tiny head. A couple months ago, I had a handful of volunteers come up where the the rapini was. Most have leaves that generally resemble the rapini, but itās putting out a head that looks like a tall broccoli. One looks to be a full sized bok choy. Both have very pleasant flavor, in spite of it being the hot season. And I have a packet of seeds I saved from that rapini. Needless to say, I will be doing that experiment again next year.
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