Both Jewel and Caroline are hybrids. Jewel has red raspberry ancestry and Caroline is derived from Autumn Bliss, - itself a polyhybrid.
Here’s the patent for Caroline
https://patents.google.com/patent/USPP10412P/en
Caroline does contain black raspberry genes. Most modern cultivars derive their fruit firmness from rubus occidentalis.
Now if you can direct your ocd towards reading and re-reading scientific papers it will seize to be a disorder and turn into a cognitive super power. 
As for tetraploid hybrids between blackberries and raspberries… they’ve been reported to yield inferior plants with astringent, mushy berries that do not separate from the receptacle. Afaik they’ve only proven useful in crossing with higher ploidy blackberries.
I’ve also been reading this study on fragaria x potentilla hybrids. It appears that hybrids between fragaria and the closely related potentilla genus are literally a dead end on a diploid level.
A musk strawberry hybrid on the other hand could work resulting in 4x offspring.
The number one problem I see with hybridizing fragaria with rubus is their much more distant genetic relationship compared to fragaria and potentilla. We’re talking tens of millions of years of divergent evolution.
If such a hybrid could be produced it would probably be a very confused little plant.
For starters what we perceive as a strawberry fruit is actually a different plant structure than a raspberry fruit. A raspberry fruit is a single druplelet of a compund fruit that contains a seed, quite comparable to a cherry.
The fruit of a strawberry plant is actually the seed, or more accurately the achene. It’s pretty much comparable to a nut. The fleshy, juicy part that we call a strawberry is just the swollen receptacle.
Now if we were to hybridize fragaria and rubus in a lab or something it would probably have a fruit intermediate between the two. That is, a raspberry drupelet and a strawberry achene. Doesn’t sound very appetizing.
For these reasons I don’t really see much practical applications for such a hybrid. It would be a curiosity for sure but I can’t imagine much potential beyond that.
The link: https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1601-5223.1971.tb02372.x
My heart broke a little, reading this. I’ll have to take what I can get and breed with whatever I have on hand. Most raspberry varieties are either untested or intolerant of my climate, so I can’t afford to be too picky. If I succeed in breeding a decent purple berry with noticeably intermediate flavor and phenotype, I’ll be happy.
For that matter, should I cut out the middleman and start my project with an established purple berry? Which variety comes closest to a middling phenotype? I hear Royalty tends towards Red. Glencoe looks really good, and I dig the thornlessness. I’m not too familiar with other varieties.
Tangent: is Joan J. a tetraploid or a diploid?
I concur! I actually have loads of papers stored in my files. The issue in this particular case is that I’m more literate in supra-species taxonomy. Varietal pedigree is a bit more impenetrable to me, especially when half the varieties used in breeding are named with alphanumerical codes. As you could see in a previous post, I hadn’t even understood that several old thornless varieties were ursinus-free.
How strange… How many people have tried? And with which varieties? Were the results consistent?
All the greater reason for my fascination! I’ve had a strange fixation on interspecific hybrids since I was a kid. The greater the distance, the more miraculous it was that such a thing could even be possible.
The marvel is not that the bear dances well, but that the bear dances at all.
If I could get any hybrid plant, I’d be decently happy. In the not-too-likely event that I get something edible, I’d be ecstatic. If I actually get something good and productive, then I’ve hit the jackpot! It’s certainly worth a few shots.
I’m glad you brought that up! As far as I can tell, strawberry achenes and raspberry drupelets seem to be the same thing, or at least they’re composed of the same tissues. The big distinction seems to be whether they develop hard and dry or as soft fleshy tissue (it’s just like the berry-bearing conifers, where the fleshy “fruit” are just cone scales that develop as soft tissues). The raspberry receptacle seems to be the same as that of the strawberry as well, just differently developed. Look at this raspberry picture, doesn’t the receptacle look almost like an alpine strawberry?
The big difference between raspberry and strawberry fruits seem to be which part develops dry and which part develops tender: strawberries are dry fruits on a tender receptacle, raspberries are tender fruits on a dry(ish) receptacle.
I get the feeling it would more closely resemble a bramble, with fleshy drupelets. Burbank’s hybrid managed to set some poorly developed fruit, and despite being more strawberry than raspberry (4 strawberry chromosomes, 1 raspberry chromosome), it developed bramble-like drupelets.
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Going back to this comment, it seems @greentechnician ’s hybrid might actually be more likely than we thought, though it’ll need work. According to http://bulbnrose.x10.mx/Heredity/Burbank/BurbankPrimus/BurbankPrimus1914.html , Burbank succeeded in crossing the diploid allegheniensis Crystal White Blackberry with the Shaffer’s Colossal Raspberry. After some further breeding of the progeny, he eventually arrived at the Paradox Berry in the F4 generation, with good flavor and intermediate phenotype between blackberry and raspberry. Whether there was any chromosome doubling event, I cannot say, but it seems to bode well for diploid breeding, with carefully selected parent stock.
One thing that seems really weird to me is that the confirmed diploid Snowbank was descended in part from the confirmed tetraploid Lawton. I have no idea how to reconcile that chromosomal math, unless something went wrong in the record-keeping.
I also think interspecific hybridization is cool but I agree with @BerryAllen here that strawberry/rubus probably is not the greatest one due to the very different fruit development.
For more distant hybrids, one would have to go for somatic hybridization, but it seems tricky.
Here is one attempt which makes me think that rubus/prunus would be cool
A peach/raspberry sounds delicious
But even just attempts at recreating 6X blackberry/raspberry hybrids can fail.
https://www.tandfonline.com/doi/full/10.1080/11263500112331350660
Also note that somatic hybrids are considered GMO in the EU
Hundreds of raspberry-blackberry hybrids have probably been created over the years. As to which varieties were used, I don’t know. Probably some of the early tetraploid raspberries with different rubus fruticosus selections.
Horticultural reviews is a good source of information on raspberry breeding. I was referring to this paragraph here:
And I’ve also read elsewhere the tetraploid crosses aren’t really a best of both worlds situation. Higher ploidy crosses seem to make better quality berries.
It’s hard to say what happened in Burbanks crosses as he did all of his work before we knew about chromosomes and only a fraction of his plants still survive. It does sound like chromosomal doubling might have taken place quite frequently. Hot climate = unreduced gametes. Just a theory. Chromosomal reduction also happens. You can get a diploid out of a tetraploid and vice versa but it takes numbers.
My biggest beef with higher policy levels is the amount of crossing and backcrossing required to fix certain traits (doubly so for recessive traits). It took years of work for the UofA program to start getting varieties that simultaneously bore the thornless and primo-fruiting traits, and that’s merely at the tetraploid level.
So what I got from this little gem of a paragraph is that Brazos, a founding member of modern Eastern Blackberry breeding, and the UofA line in particular, is the grandchild of a raspberry… I rest my case, there are no modern raspberry-free blackberries. Westerns have dewberry & loganberry parentage, Easterns have Brazos, and even modern European types have R. caesius. I’ll have to stick to the old diploid varieties and the confirmed wild tetraploid species. I put the R. armeniacus back into my eBay cart.
On a more personal note, I’m panicking. The tiny mail order raspberry plants I recently got have been dying off. Both Jewel and Ohio Treasure are dying, and they don’t look like they’ll recover. I chopped off the top of a burnt-looking Caroline in the hopes that it’ll resprout from the roots (as it had the first time I grew it years ago). I don’t exactly have loaded pockets right now, each purchase is a bit of a sacrifice, so every loss hurts me straight to the heart. 
Thornlessness has actually been easier to work into higher ploidy (6x - 8x) blackberries. They used Austin thornless most often and it has a dominant gene for thornlessnes and is octaploid. You get thornless plants in the F1. Sometimes higher ploidy makes things simpler.
It is my understanding that none of the raspberry genomes made it into Brazos. They wanted to introgress the heat tolerant, diploid Texas dewberry into tetraploid blackberries and through Nessberry they did. Brazos probably only got the dewberry side and the incompatible raspberry side got dropped off in subsequent generations.
Are they in full sun?
This was incorrect, not sure what I was thinking at the time. Joan J is 2n as are most Raspberries. ‘Joan J’ is from cross ‘Joan Squire’ × ‘Teri-Louise’ FWIW. Some info that may be of interest https://www.biorxiv.org/content/10.1101/546135v2 (the PDF download is free) also from the breeder of Joan J: Autumn Fruiting Raspberries: keeping up with the Joans - Joan Morgan's Fruit Forum
Tayberry had a 4n raspberry parent, cultivar name unspecified.
I think the Russian raspberry Gordost Rossii is supposed to be 4n and is sometimes available, There’s one from a random seller on eBay ATM, but it’s not expensive and who knows what you’ll get.
I have a bunch of treated raspberry seeds sprouting hoping to make my own 4n. I have been unable to find info for optimal time/concentration using oryzalin on raspberries and blackberries and I’m not equipped to work with colchicine these days, so it’s trial and error for now.
I find the little plug size plants I’ve bought can’t take much light or heat until they get going, usually 4-8 weeks.
I learn so much with each of your posts. Thank you! 
Do you have a source for it? Or do you know where I can source it? It would be simpler for me to rely on the commercial varieties rather than having to track down the wild types.
My need for varietal purity and mid-way crosses is rather arbitrary, but it only extends as far as my breeding efforts. The way I see it, if any extraneous genes are present in a particular plant, they may disproportionately affect the fruit’s presentation in subsequent crosses. If there’s already raspberry in a “blackberry” variety, would crossing to a raspberry produce a more raspberry-like fruit than it ordinarily would’ve? It’s not a bad thing if the result is a quality berry, but I am aiming for mid-way phenotypes (again, just for arbitrary reasons). And there’s a chance I’m completely off-base here.
They receive direct sun in the mornings, but spend the afternoon in shade. The weird part was that they were just fine under this arrangement the first week, then suddenly wilted and died off after I watered them for the second time since their arrival.
I’m still hopeful that Caroline might come back from the roots, but both my blackcaps seem dead. Most of the other plants from the order are still doing fine.
Duly noted! And thank you for the info!
Joan J. was actually my first choice of Red Raspberry for its primocane fruiting and thornlessness, but I haven’t succeeded in acquiring a live plant, only a pair of dormant ones… every dormant bramble I’ve ever tried died off, they don’t awaken properly in the tropics. Live ones, on the other hand, have grown well for me over the years.
Please keep us updated on that! Where did you get the Oryzalin? I haven’t tried chromosome duplication yet, but for germination purposes, I got a bottle of Sulfuric Acid. It’s in storage, and I’ve chickened out of using it in favor of Hydrogen Peroxide. I also found Gibberellin on eBay, but haven’t purchased it yet (and I’m not sure how to use it with Rubus seed).
Had I known, I would’ve kept them in full shade from day one, no morning sun. The Crandall Currant also withered up, and the male hardy kiwi is quite probably dead. The initial soil smelled a bit rotten in all cases (including the survivors).
I’m glad to be of help. I won’t be much use in sourcing Brazos though. I don’t really keep track of North American vendors nor hot climate cultivars. I have however seen imported blackberries from Mexico that I thought could have been Brazos. I think it is or at least used to be the most commonly grown variety in Mexico and Brazil.
Would you happen to have a source for the part about rubus ursinus containing salmonberry genes? I haven’t found a lot of information on the genetic make up of the species so anything could be useful.
Where did you read about Gordost Rossii being tetraploid? I bought those plants from Ebay last year but haven’t found any mention of the ploidy level.
Honestly, I don’t remember where I read it, so I might be completely wrong. A cursory search turned up nothing. However, ursinus seems to contain some Idaeobatus genes. From a sudy previously posted here: https://growingfruit-images.s3.dualstack.us-west-2.amazonaws.com/original/3X/3/0/30c947ea2593a214eb474ccc0b6c7d180ca9570c.pdf
Oddly, while this study indicates that R. ursinus and R. macraei aren’t particularly closely related, other studies conclude that they are.
fulltext.pdf (1.3 MB)
morden2003.pdf (378.2 KB)
When I first saw the plant (on ebay for big $) I started searching right away…large fruit and diverse genetics…East x West…
As this is a Russian cultivar and I have a little experience with the language I searched mainly in Cyrillic.
Гордость России - Pride of Russia. A lofty title indeed as per grower report. You would not believe other name candidates at all.
Found much of interest but ended for me when I found a detailed post by a Russian grower which basically said the flavor was not so great. Larger/fatter size most frequently comes with an increase of ploidy from 2n to 4n so I did not chase down the large number of results for 4n/tetraploid when searching for only the name after finding grower report. Yandex is (soon was?) the premier search engine for Russian and other Cyrillic languages, best computer translations too.
DM for more info if you like and I will try to get back in a couple days.
@Caesar
The genetic biology portion of the work by Carter et al is of the highest quality. However, the mathematical method they employed for clades/grouping is at most wishful thinking. It is an approach gaining much favor in biology journals so I suspect it is not their error for chosing it. Be suspicious when you see "“bootstrap”, “burn-in”, and “Bayesian clustering”. Even the original authors of these methods state that the computations have a nearly zero confidence interval and the results are only a few of numerous possibilities.
