Sunday, 8 April 2018

Strawberry Raspberry hybrids

Have you ever heard of a plant that is the hybrid of a strawberry and a raspberry?  Have you ever seen one?  Have you made that cross yourself?  I have.

I am not talking about a strassberry, which is just a variety of strawberry, I am not talking about a GMO or something produced through somatic protoplast fusion, I am not talking about Rubus illecebrosus (which is not a hybrid at all), I am not talking about a grafted plant.  I am talking about cross pollinating strawberry and raspberry, and growing out the hybrid seeds.  These are true intergeneric hybrids that I am referring to.

A few years ago I read a post on a blog called 'The Biologist is in' about some plant breeding work done by the late Luther Burbank.  I found this blog post to be inspiring, so I went on and read more about Luther Burbank and his strawberry raspberry hybrids in other places.

Luther Burbank was a remarkable plant breeder, he crossed a raspberry with a strawberry about one hundred years ago.  He didn't use crazy chemicals or GM technology, he also didn't know a lot about genetics.  At the time this kind of hybrid was thought to be impossible and many people mocked him.  We know a lot more about genetics because Luther kept doing things that were considered impossible.  I can't find any reference to anyone actually attempting to cross strawberry and raspberry since then.

Luther Burbank's raspberry strawberry hybrid. 
Picture from http://bulbnrose.x10.mx/Heredity/Burbank/Burbank_raspXstraw.html

This got me thinking: if a man one hundred years ago with very little understanding of genetics could cross strawberries and raspberries then there is no reason that I can't do it today.  So I tried to cross strawberries and raspberries, and I succeeded.



Luther Burbank's raspberry strawberry hybrid plant was completely thornless, apparently it was very vigorous and flowered like crazy - far more than either parent.  It set a few seedless drupelets but never really fruited.  As it was never going to be a commercial success eventually it was destroyed.  Unfortunately there is no surviving description of the taste of these seedless drupelets nor are there any of this plant still alive, Luther destroyed them all deliberately.   He did a lot of killing his experimental plants for fear of casting pearls to swine.  It is such a waste.  It meant that I had to start from scratch.

We can't be completely sure why Luther Burbank's strawberry raspberry hybrid did not set fruit, that being said there are two likely reasons.  One is simple to overcome by choosing the right parent stock, the other is a bit more difficult to overcome but I should eventually be able to fix it if this is the problem.  I was careful in choosing parent stock for my hybrid plants, so I should find out soon enough if that was the only reason that Luther Burbank did not have much success with his hybrid. 

Strangely, through all of my research, I did not find any example of anyone who has actually attempted to recreate this cross since Luther Burbank's attempt.  I found plenty of people saying not to try it as it is too difficult, and some saying that they intend to attempt this in the future, but no one who had actually attempted it and had any information to offer from their experience.  Even if someone tried and failed I would have learned from it, but I found no one who has said that they have tried.  If you or anyone you know of has ever attempted (successfully or otherwise) to cross strawberry with a raspberry let me know, I would love to talk to them.

Potentially I am growing the only strawberry raspberry hybrids in the world.  My tiny strawberry raspberry hybrid seedlings are slowly growing larger each day.  Hopefully they will flower next year and I will be able to see if they can set fruit.  I have high hopes that they will set fruit for me but even if they don't this will still be remarkable.

Many many things could go wrong from here.  If any of my strawberry raspberry hybrid seedlings survive winter I will take some pictures and write an update in spring.  If none survive I will plant more seed in spring as well as try more crosses next year.  I think it is all very exciting.

I do sell perennial vegetables and heirloom vegetable seed on my for sale page.  Even if all goes well it is unlikely that I will be able to offer strawberry raspberry hybrids any time soon.

14 comments:

  1. Will be interesting to follow your experiment. The closest I know of is the Japanese Strawberry - https://www.chrisbowers.co.uk/product/hybrid-japanstraw/. Also https://www.pfaf.org/user/Plant.aspx?LatinName=Rubus+illecebrosus. However I believe the flavour is not wonderful raw. Great to see you trying to breed this variety again.

    ReplyDelete
  2. Hi Anne,

    I have never grown Rubus illecebrosus, but my understanding is it is one of many species of Rubus that has neither raspberry or strawberry in its heritage. I am told that it was (and still is) sold by less scrupulous companies as a hybrid of the two when it is not, it is a separate species. One of its common names is "strawberry raspberry" as it kind of looks like both of them, not because it was bred from them.

    I am super excited that my strawberry raspberry hybridisation attempt seems to have worked, and can hardly wait to see if it ever fruits. If any survive winter I am sure I will put up some pictures, if they all die I still have some seed so can replant in Spring. Lots of fun!

    ReplyDelete
  3. Hi Damo! I'm Caesar from the Tropical Fruit Forum. I read the same information from Burbank's book and tried my hand at breeding the hybrid on three occasions between 2015 and 2016. I was unsuccesful and took a break from the project due to other matters, but I'm hoping to try again this year, if circumstances allow. I haven't actually posted about it on the forum yet as I was hoping to have results for a big reveal, but I did seek advice on cross-pollination.

    I was already growing Fragaria vesca to experience its renowned taste when I acquired a raspberry plant. Reine Des Vallees was the Alpine Strawberry, and I chose Caroline as the Raspberry because it seemed well-suited to my Puerto Rican climate. And then it hit me: both species were diploid! (with a haploid count of 7). I could try my hand at Burbank's work with
    improved genetic information!

    On the first two attempts, I isolated the raspberry's flowers with plastic candy bags, but on the third I just snipped off any newly-forming flower buds to save myself the hassle (I only had the one plant, and people rarely grow raspberries here). On all three occasions the flowers withered a week or two after pollination, and that's when I sought the advice. I was told to try "Mentor Pollination", and I decided that would be my next step but I had to put it on hold. I'm repotting the plants this year to get some good growth before the next flowering season.

    Truth be told, I'm not entirely certain that Caroline is diploid, as I found no online source that revealed its ploidy. For all I know it might be one of the tetraploid R. idaeus, but I hope that's not the case. I had also heard that strawberry pollen is heat sensitive, but that doesn't stop my alpines from fruiting up a storm, so I doubt that was a problem for me. Perhaps it was the fact that I dried the strawberry pollen in an open jar for a day (instead of using fresh pollen from a fresh flower).

    You mentioned two potential reasons for Burbank's failure. Was one of them ploidy? And what of the second one?

    What parent stock did you choose? How did you go about pollinating? And how'd you get the seeds to sprout? I've had terrible luck trying to germinate pure-bred Rubus seeds before, though they were admittedly dried seeds and they're better off fresh.

    Post some pictures! I'm dying to see what those suckers look like in-vivo.

    Also, did you read the article on Father Schoener? (http://bulbnrose.x10.mx/Roses/breeding/Schoener/SchoenerCD1938.html). Apparently, he succeded in breeding Rosa pomifera with a Spitzenberg Apple, and the hybrid actually bore fruit! Unfortunately, I think it was one of the plants that succumbed to the fire on his property, as I've seen no further record of it being grown by anyone else. I'm planning on attempting this hybrid too, but I think I'll have a tough time procuring the genetic material; R pomifera is usually regarded as R. villosa these days, but I'm not sure if the two are identical in genetic traits (like ploidy)... Schoener's particular stock might have been different from any Villosas I find.

    ReplyDelete
    Replies
    1. Hi Caesar,

      Ploidy is one of the potential reasons for Burbank's plants not fruiting. I only used parent stock which were diploid to avoid this.

      Another issue can occur when two species have the same number of chromosomes, but the chromosomes are too unrelated. The hybrid fails to generate gametes as the chromosomes won't line up during meiosis. The result will be a haploid with an increased basic chromosome count. This may be caused by a high level of structural rearrangements in the chromosomes of strawberries compared to raspberries, even if the genes are otherwise compatible. Inducing polyploidy in any surviving plants should remedy this.

      So far some seedlings have already died, some will die shortly as they are albino or partial albino, and I am happy to say that some are green and look strong. Many things could go wrong, but I hope a few survive winter.

      I have some seed left over to plant in Spring, plus I made a few more crosses that appear to have taken. I will write another post on this.

      Delete
    2. I forgot to say: I thought the rosa x apple was a hoax? I will have to read more about it, thanks for the link!

      Delete
    3. Oh, like the Triangle of U? It hadn't occurred to me that Fragaria x Rubus could end up crossing like the Brassicas. That certainly adds another layer of complexity. Inducing polyploidy is done with Colchicine, right? How does one go about using that in a domestic environment?

      And speaking of the Brassicas, there have also been hybrids done between them and radishes. Raphanobrassica or Brassicoraphanus (https://en.m.wikipedia.org/wiki/Brassicoraphanus). I think they've been geared toward animal forage and leafy greens so far, but I'd like to try my hand at a root crop (Radish x Turnip or Radish x Rutabaga). There's also Onion x Garlic hybrids (https://www.hort.purdue.edu/newcrop/proceedings1999/v4-374.html) (https://link.springer.com/article/10.1007%2FBF00215036), but they required embryo rescue to achieve the first viable generation (not to mention inducing fertility in the garlic), so I don't think I'll try that one, though I'd love to get the hybrids themselves, if they ever make them available.

      Hybrids of all kinds fascinate me (particularly from highly disparate stock), and I'd love to take a stab at Burbank's mass Rosaceae pollination to see what else can be achieved, though perhaps less haphazardly.

      Schoener's hybrid seems to have been real; there's another article penned by a different author that refers to it as a runt fruit with a rose-like taste, and that it made good jelly. (http://bulbnrose.x10.mx/Roses/breeding/Schoener/SchoenerLD1937.html)

      Regarding Fragaria x Rubus, I was also hoping to try with other diploid stock, like R. occidentalis (the black raspberry), R. ulmifolius (the - usually - diploid blackberry), and others. Then there's the hexaploid F. moschata x R. chamaemorus, but that'd be particularly difficult for me (that Rubus is highly heat sensitive).

      Delete
    4. Also, if it was real, I wonder if Schoener's fruit was fertile or apomictic. It was referred to as runtish, but that was probably by apple standards, and it was certainly usable (not like Burbank's tiny drupelets).

      Delete
    5. Hi Caesar,

      Inducing polyploidy at home can be a bit hit and miss but isn't overly difficult if you give it enough attempts. I used to do it in highschool with Drosera and the results were interesting. I used to kill some plants by accident, but if you give it enough goes you end up succeeding.

      The hardest part iss getting hold of the chemicals. Back then it was simple to get a pre-emergent herbicide containing oryzalin. I am not sure if they sell it anymore. I have seen something in Bunnings with oryzalin and glyphosate, so I assume if I look hard enough I should be able to find something with just oryzalin.

      If I can't find any, then colchicine works, but is not as safe to handle and can also be difficult to buy. It can be derived from autumn crocus pretty easily. One of the issues with making your own from crocus is it's impossible to know how much to use when you have a chemical of unknown potency.

      I have another year or more until my seedlings are large enough to flower, then probably another year or two to build up numbers before I can attempt to induce polyploidy. Fingers crossed none of this is necessary and they fruit just fine.

      Schoener's hybrid sounds fascinating. I am reading as much as I can find on the topic. I often ask myself why people don't attempt to make these crosses anymore. Even raspberry blackberry hybrids, which are simple to create, don't seem to be done by anyone anymore. None of the hybrid berries are really suited to small gardens, but the fruit is so tasty and delicate that they should only be grown at home, so they desperately need more breeding effort put into them.

      I would also love for someone to cross blackberry with a rose, I am unsure if it is possible. Unfortunately I don't have access to the right germplasm to even attempt such a cross. I am not sure how much luck I would have using random pollen collected from people's gardens and roadside weeds!

      Delete
    6. Hi Damo!

      Thanks for the tip, I'll look into the Oryzalin. I like the idea that I can do this with a safer compound now.

      I've taken some time to review Schoener, Burbank and Michurin, and was hit with inspiration. I listed most of the important (and several minor) edible species in the Rose family, divided in three clades, and looked up their ploidy. Prunus is X=8, the pomaceous Malinae is x=17, and the Rosoideae is x=7. They're long term plans, but I hope to be able to produce good work on par with those original authors that have so inspired me. I found a very interesting document, detailing many of the Malinae hybrids that have been done (I’d like to get my hands on x Sorbomespilus “Desertnaja”; it sounds tasty). (https://www.agroforestry.co.uk/wp-content/uploads/agnews-sample/AGN_sample.pdf )

      Prunus have several species of plums, cherries, peach and apricot; most are diploid. The pomaceous list is the longest one; mostly diploid as well, they include Apples, Pears, Quince, Medlar, Hawthorns, Serviceberries/Saskatoons, Aronias and Rowans. I'm particularly interested in crossing apples and pears with saskatoons (which are said to be blueberry-like in taste + almond notes) and Medlars (which often impart cinnamony sweetness to their hybrids).

      The right germplasm would make the best difference, but it’s always worth a shot. I think it should be as easy as crossing strawberry and raspberry; Fragaria, Rubus and Rosa are the three edible-fruited genera of the Rosoideae (also Duchesnea, but it’s pretty insipid). Weirdly, while Rosa and Rubus look more similar to one another (as plants), the taxonomic trees I’ve found tend to place Fragaria and Rosa closer to one another, with Rubus at a more basal position.

      I actually have a weird theory about Rose hips… I liken them to Figs. Figs are essentially inside-out mulberries. The tissue that turns into the mulberry’s core develops in the fig as the outer surface, leaving the flowers in. The rose is not quite so extreme, but despite Schoener’s hybrid, rose hips are not pomes: they are said to have achenes on the inside. Achenes are what a strawberry has, and they are homologous to raspberry drupelets (developing as dry achenes instead of juicy drupelets; the raspberry core equates to the strawberry’s main fruit structure underlying the achenes). What I’m thinking is that a rose hip’s outer wall is like an inside-out raspberry core, and perhaps the achenes equate to the drupelets (similar to a fig’s relation to a mulberry). This is wild speculation on my part, but it makes me wonder if anyone’s done any studies on the homology of tissue development of these fruits.

      More people should definitely get in on the fruit-breeding action. I think there’s great discoveries to be made, and great new fruits to try, if only people gave it a shot.

      Delete
    7. Note: If the pdf link on Malinae hybrids fails to open, try it on a phone. It opens fine on my phone's browser, but it takes me to an error page on my computer.

      Delete
  4. Hi Caesar,

    I used to have a medlar tree when we had orchards and acreage, they are one of the most beautiful/ornamental of fruit trees. The fruit is ok after bletting. I never thought of trying to hybridise medlar with anything. I am kicking myself now. What a wasted opportunity. My neighbour has a medlar, perhaps she will let me take a cutting to graft onto an apple or something...

    Saskatoon are fantastic. I ate heaps while in Canada. They were like a huge sweet blueberry. I know they are in Australia but have not been able to get one. If you have any ideas where I should ask I would be interested.

    I am going to do some more reading on the rest of your post. I must admit, I find your ideas both fascinating as well as inspiring! Keep up the great work.

    ReplyDelete
    Replies
    1. Medlars are graft compatible onto pear.

      Delete
    2. Do post any and all progress; I'd love to see what comes of your experiments. I'll be posting my own back at the forum as I progress. And speaking of, I've found that Rosa rugosa is a diploid fruiting rose that would be a better match for some of my experiments, so I'll be giving it a try as well.

      I get the feeling Saskatoons like the cold too much for my own climate, but that won't stop me from trying them. As for finding them locally, might I suggest joining the forum? Our members are worldwide, with several from Australia, and we have some classifieds sections where people can buy, sell and trade material. And if the members have no such materials, they may still direct you towards local suppliers. I've gotten quite a few rare plants myself there.

      Thanks! I'm glad I can inspire with some of this crazy stuff, and I hope others hop in to try their hand as well. This is a very under-explored topic that deserves more attention from plant breeders, professionals and amateurs alike.

      Delete
    3. Hi Caesar,

      I finally got the photos off the camera and put them up here: http://living-mudflower.blogspot.com/2018/07/strawberry-x-raspberry-hybrid-plant.html

      I didn't realise until I got the pictures off the camera that they have grown considerably since those pictures were taken. At this stage they look very much like strawberry plants. The leaf edges are very jagged and they seem to curl over a little. Hopefully at least one survives winter.

      I have been doing some reading into wide crosses, and it appears that many things I was always told could not cross have been crossed several times by various people. Apples and pears, European pear and Asian pear, etc. Some of the issues with hybrid necrosis in fruit trees appear to be overcome by growing at different temperatures or grafting to compatible rootstock.

      Fascinating stuff, it has got me thinking about trying a few crosses. I wish I had more land, water and more time to try these things!

      Delete