Rhubarb breeding

[Dominic J]

From my research, cultivated rhubarb is "always" tetraploid, while wild species are diploid or tetraploid, depending on which.

If you've got any source on diploid cultivated rhubarb, I'd be curious to learn about it. Otherwise, they could probably mate with diploids, or anther culture could be attempted.

Here's what one source has to say:

The name Rheum rhaponticum Linnaeus appears to have been misapplied widely to R. rhabarbarum in North America. Rheum rhaponticum, European rhubarb, is the only member of the genus confined to Europe. Rare in the wild but widely cultivated, it is a diploid (2n = 22); R. rhabarbarum is a tetraploid (B. Libert and R. Englund 1989). A chromosome count of 2n = 44 reported for R. rhaponticum from Wisconsin (N. A. Harriman 1981b) probably is from R. rhabarbarum.

[nathanp]

For Rheum x rhabarbarum, yes those all appear to be tetraploid, probably became polyploid through it's hybridization.

There are several diploid species that are cultivated in some parts of the world, though most appear to be sold as ornamental and not edible. 

I had requested several accessions through the USDA genebank last spring, but had to put this breeding project on hold for the moment.  Due to COVID concerns and limited staffing, the USDA was unable to ship my requested material last spring.  One of the accessions was a diploid accession of Chinese Rhubarb (Rheum palmatum).

[Garrett Schantz]

Strictlymedicinalseeds sells a decent amount of Rheum species.

Rheum officinale
Rheum emodi
Rheum rhaponticum
Rheum nobile
Rheum alexandrae
Rheum palmatum tanguticum
Rheum rhabarbarum

No idea which are tetraploid/diploid but the website sells these as medicinal / edibles. Might be worth a try I suppose. Found these a few months ago when I was considering Rheum hybrids that would focus on lowering oxalic acids.
 Etsy has some Rheum species as well.

[nathanp]

Ha.  pretty funny with some of the Q&A on their website.  About half of those other species are listed as having laxative properties.  I'm not sure that's a breeding project I'd prefer to begin, to select away from laxative properties.  Makes you wonder what people put up with to domesticate the edible one.

[Garrett Schantz]

Rheum nobile seems like a safe one and it can probably be used as an ornamental at the same time, but yeah a lot of the wild species have laxative properties - not toxic but not something I would want to experiment with either.

[Dominic J]

Upon further investigation, I'm not finding a lot of info on the edibility of these other species. Very little saying rhaponticum is cultivated for what is implied to be the stem, but for the rest? The only mentions I find are of medicinal uses, and root or leaf uses, but not if their petioles are a good thing to put in pies.

I'd be reluctant to use any of these other species in a breeding project without more information on the edibility of their stems.

[Garrett Schantz]

The stems seem to be more or less the same as the rhubarbs normally used for pies. Rhubarb is high in oxalic acids and gives off a sourness. If anything some of the wild types could help reduce that.
 Rhubarb is also cooked for most of its uses, so there is that to consider. Eating raw common rhubarb regularly would be toxic as well.

[nathanp]

I found plenty of links that referenced all the other, non cultivated (as edible) species have medicinal or herbal traditional uses ... as laxatives. 

https://thenaturopathicherbalist.com/2015/09/25/rheum-palmatum/

[Garrett Schantz]

Should be easy to breed out. Anything from GRIN probably has the traits as well.
 If you google "laxative rhubarb" you can see it gives a lot of people mild diarrhea effects after heavy consumption. So the common type is probably just lower in whatever chemicals cause it.
 Some research says it can actually prevent diarrhea as well due to tannins. There isn't much info on the wild species, but I doubt its going to be a sudden explosion.
 
The website you posted is using Rheum palmatum as a powder, decoction, tincture. So its probably higher doses than just cooking the stem up for use. Although its probably going have a higher effect than the "edible rhubarb". Oxalic acid is probably the largest concern for this species.

[Dominic J]

Should be easy to breed out. Anything from GRIN probably has the traits as well.
 If you google "laxative rhubarb" you can see it gives a lot of people mild diarrhea effects after heavy consumption. So the common type is probably just lower in whatever chemicals cause it.
 Some research says it can actually prevent diarrhea as well due to tannins. There isn't much info on the wild species, but I doubt its going to be a sudden explosion.
 
The website you posted is using Rheum palmatum as a powder, decoction, tincture. So its probably higher doses than just cooking the stem up for use. Although its probably going have a higher effect than the "edible rhubarb". Oxalic acid is probably the largest concern for this species.

Is that powder made from the petiole, though? Because the sources I read seemed to suggest it was the roots that were used as medecine, in Asia.

It's also not very clear what's toxic in rhubarb leaves, and it's possible other species would have those compounds in the petiole. I highly doubt oxalic acid's the problem: you've got that in petioles plenty, and you also have more oxalic acid in some veggies than you do in rhubarb leaves.

[Garrett Schantz]

Rhubarb usually has more oxalic acids than other vegetables which is why it is cooked. Wild species can have a lot more pr less. The "toxic" chemicals listed in a lot of the species just causes diaherria which edible rhubarb can also do.

[Dominic J]

Rhubarb usually has more oxalic acids than other vegetables which is why it is cooked. Wild species can have a lot more pr less. The "toxic" chemicals listed in a lot of the species just causes diaherria which edible rhubarb can also do.

Except that cooking does nothing to oxalic acid. Blanching can leech away some of the OA, but I don't know anyone who bleeches rhubarb.

Also, rhubarb leaf does not have all that much more OA than rhubarb petiole, only about 50% more per weight. Also, petioles have a lot more weight than the leaf blade, so if you ate a whole leaf, more of your OA would come from the petiole than the blade.

But spinach, purslane, and parsley have more OA than rhubarb leaf. Like, 250% the concentration of OA in parsley compared to rhubarb leaf. And I never heard of anyone blanching those.

So if rhubarb leaves are toxic, I don't think OA's the culprit.

[Diane Whitehead]

There are several edible species mentioned in Cornucopia II A Sourcebook of Edible Plants

Rheum australe   Leafstalks are eaten raw, cooked, preserved in salt, made into preserves, or dried and stored for future use. They are said to have an apple-like flavor.  Young shoots that have been blanched as they emerge from the soil are white, crisp and free from fiber.  Himalayan region   (syn R emodi)

Rheum officinale  In Italy and China, the dried rhizomes are used for making tonic wines and other alcoholic beverages. Extracts of the roots are ... used in bitter tonics, carbonated beverages, syrups, liqueurs, candies etc  Eastern Asia

Rheum palmatum The leafstalks are sometimes eaten or made into wine and preserves.  Mongolia

Rheum ribes  The leafstalks and fresh stems are eaten raw or cooked.  Larger petioles are made into pies or preserves and are said to have the flavor of currants.  In eastern Turkey they have been considered a delicacy since the 13th century.  Southwest Asia

===============

And a different use for our common rhubarb:  The young inflorescences resemble cauliflower and may be deep fried or boiled and served "au gratin" with cream sauce.
 

[Garrett Schantz]

The only thing I could find that could potentially cause any harm is the oxalic acids in more cases.
 The whole diaherria inducing element seems to be what the "toxicity" toxic doesn't have to mean deadly.

[Dominic J]

The only thing I could find that could potentially cause any harm is the oxalic acids in more cases.
 The whole diaherria inducing element seems to be what the "toxicity" toxic doesn't have to mean deadly.

One source I came upon, I don't remember how reliable it was, stated that the UK gov recommended people eat the leaves instead of discarding them during WW2, but then people got sick *and died*, and so they stopped saying to do that.

If that's true, and people literally died, then that's pretty strong evidence that there is more than OA at work here. I think I had read something about glucosides elsewhere. Some of this was probably from wikipedia, which may or may not have had sources for it. It doesn't seem like there was much serious research put into "why shouldn't we eat rhubarb leaves?".