Intergeneric hybrids

The other day someone linked to my post on strawberry x raspberry hybrids on Reddit and my blog post got a lot of views.  While this was really nice, I made the mistake of reading some of the comments in Reddit.  My opinion of humanity dropped somewhat when I noticed that many of the people arguing had little to no understanding of what they were saying.  Their claims were based on aggression and making up a guess on the spot, rather than any form of evidence or research.

One person claimed that intergeneric hybrids (hybrids between two different genera) cannot exist.  This person likened the possibility of a strawberry raspberry hybrid to crossing a human with a goat.  Initially I was tempted to make nasty comments about this person's lack of basic knowledge.

Then I thought about it some more and decided rather than chastise them for their ignorance and belittle them for making claims that they clearly have never researched, maybe this could be used as an educational activity.

Bumpy irregular strawberry x raspberry hybrid

Intergeneric hybrids do occur in nature.  They have been seen in plants as well as animals.

Some closely related genera are possible to hybridise, while others will never hybridise.  The ones that are possible are always closely related genera.  Strawberry (Fragaria) and raspberry (Rubus) are relatively closely related.  Human and goat are not.  Even with this knowledge trying to compare the possible cross between Rubus and Fragaria to a goat/human hybrid is completely absurd.

Intergeneric hybrids occur in animals as well as plants.  Intergeneric hybrids can be found among mammals (they are strangely common in cetaceans), birds, and reptiles as can be seen in the examples below:

Mammals: Tursiops Delphinus hybrid: https://www.nrcresearchpress.com/doi/abs/10.1139/z03-150#.XVeMDEdS_IU

Birds: Cairina Anas hybrid: https://www.cambridge.org/core/journals/proceedings-of-the-royal-society-of-edinburgh/article/xivgenetical-and-cytological-studies-of-the-intergeneric-hybrid-of-cairina-moschata-and-anas-platyrhyncha-platyrhyncha/F7FE7498CE0DA4A1641EA75E13882A3F

Reptiles:  Pituophis Pantherophis hybrid: https://bioone.org/journals/Journal-of-Herpetology/volume-46/issue-2/10-260/Two-Naturally-Occurring-Intergeneric-Hybrid-Snakes-Pituophis-catenifer-sayi-/10.1670/10-260.short

Plants and animals are biologically very different.  Many things that are common in plants are extremely rare or impossible in animals.

Proving the existence of intergeneric hybrids in animals quickly rules out the human cross goat argument, but does not do anything to back up the possibility of a strawberry x raspberry hybrid, so let's move onto plants.

Leaf edges curl - I am unsure if the cause is genetic or environmental

Intergeneric hybrids among plants:
Most people with a basic understanding of agriculture can tell you that triticale is a wheat rye hybrid.  It is common and grown on commercial scale.  Australia produces around 800,000 tonnes of triticale grain per year.  This alone proves that intergeneric hybrids among plants are possible .

Fifteen seconds on a search engine returns many thousands of intergeneric hybrids among plants, below are a few examples:

Triticum Secale hybrid: https://en.wikipedia.org/wiki/Triticale

Citrus Citropsis hybrid: http://era.daf.qld.gov.au/id/eprint/4475/

Citrus Fortunella hybrid: https://pdfs.semanticscholar.org/51b9/124a3d04b4479dbab065b7bc58088a86dbfa.pdf

Maleae intergeneric hybrids:  https://en.wikipedia.org/wiki/Maleae

Malus Pyrus (commonly known as Zwintz-scher’s Hybrid) hybrid: https://www.researchgate.net/profile/Stefan_Martens/publication/261771797_F1_hybrid_of_cultivated_apple_Malus_domestica_and_European_pear_Pyrus_communis_with_fertile_F2_offspring/links/02e7e53577214e7655000000/F1-hybrid-of-cultivated-apple-Malus-domestica-and-European-pear-Pyrus-communis-with-fertile-F2-offspring.pdf

Sorbus Pyrus hybrid: https://www.actahort.org/books/918/918_123.htm

To add more weight to the possibility of a strawberry raspberry hybrid, there are intergeneric hybrids between strawberries and Potentilla:

Fragaria Potentilla hybrid: https://www.actahort.org/books/348/348_19.htm

Now that we have demonstrated intergeneric hybrids do occur in plants (and animals), and that Fragaria are known to hybridise with closely related genera, I guess the next step it to look at my strawberry raspberry hybrid and answer some questions I have received over them.

Elongated petiolule - this is not seen in the parent species

Are you 100% certain this is a strawberry raspberry hybrid?
When attempting this cross I emasculated the flowers and bagged them prior to hand pollination.  I attempted reciprocal crosses between plants of the same ploidy to increase chances of success.  A a control I emasculated and bagged some flowers but didn't pollinate them, all aborted early and none produced seed.  I tried many crosses, planted many seeds and very few germinated, out of those most died early.  The leaves, flowers, and fruits of the surviving plant are different from the parent varieties.  Strawberry seeds planted at the same time as the hybrid seeds began flowering around 5 months old, this hybrid plant took around 10 months and then the first few sets of flowers aborted without setting fruit.  The parent strawberry throws a lot of runners from a very young age, this plant is over a year old and has not yet thrown any runners.  I have saved seed from this plant and they seem to have less than 5% germination rate, while the strawberry parent's seeds usually have over 95% germination.  Even with all of this, there is still an incredibly small chance that some tiny ant crawled in under the bag and pollinated the flower, so without genetic testing I cannot be completely certain it is a hybrid.  To answer the question: I am not certain that this is a hybrid.

Has this been independently tested and proven to be a strawberry raspberry hybrid? 
Not yet.  I would love someone to test this genetically to conclusively determine if it is a hybrid.  I don't know how to get this done in Australia.  If you are able to help please let me know.  Edit to add: I sent samples of these plants to the CSIRO who have since tested them.  They are true intergeneric strawberry raspberry hybrids.  The results can be seen here.

Unripe berry - lumpy and forked at the end

It can't be a hybrid because the berry is bumpy and ugly.  

If anything its unique looks add to the possibility that it may be a true hybrid.  This is just one of the morphological abnormalities that can be observed between this plant and the strawberry parent.  Other morphological abnormalities include the length of petiolules, flowers always being subtended by a leaf, inconsistent flower structure (such as extra petals and fewer stamens), and the absence of runners.  Germination time/percentage, early death of large numbers of seedlings, and the greatly extended time from germination to maturity are among the other factors that suggest this plant may not just be a strawberry.

This looks like a strawberry, why doesn’t it look more like an equal mix of raspberry and strawberry?  

In wide crosses there is often, but not always, asymmetric expression patterns and phenotypic similarity with the seed parent.  I am not sure why it happens in some crosses but not others.  Most of the papers I have read on this phenomenon appear to be based on interspecific crosses rather than intergeneric crosses, but there are a few papers written on triticale that suggest this strong maternal effect in intergeneric hybrids is relatively common (www.fao.org/3/a-y5553e.pdf).  So while I don't know why this happens, I know that it does happen often.

Flowers always subtended by a leaf

Some poorly worded question about fruit types eg strawberry produce achenes on a fleshy receptacle while raspberry produce drupes.

I am not quite sure what the question is here, or how this would ever support or disprove this possibly being a hybrid, so I will take a stab and try to guess what they are asking.  Usually several genes interact to create what we see in a plant or animal.  Some genes are dominant over others and if both genes are present you often only see the effects from one (ie one is dominant and the other is recessive).  The fruiting structure that we see is due to the genes present in the plant and how the genes interact with each other.  This is unexplored territory, we have little understanding of what phenotype a plant will display when it is heterozygous for fruiting in drupes and producing achenes on a receptacle.  Both parents were diploid (2n = 2x = 14) so if this is a true hybrid it and any seedlings it produces could shed light on genetic interactions that are as yet unknown.

If these are possible why hasn’t anyone done this before?  

This is one of the most common questions, it makes little sense and appears to be a self-fulfilling prophecy.  Our collective scientific knowledge in any given area isn’t as far along as people think it is.  There are plenty of things we have never attempted and all areas of science break new ground all the time.  As no one ever attempts to do this cross you assume it can’t be done.  Wouldn’t it be better if it was attempted, then proven to be possible or not to be possible?  In the past this hybrid was created using somatic fusion and the resultant plant was apparently viable, I am unsure if it fruited and have not seen any pictures of the plant.  My attempt at crossing strawberry and raspberry involved cross pollination (similar to Burbank's attempt) rather than somatic protoplast fusion.  Unlike Burbank’s attempt, I used plants of the same ploidy to increase the chance of success.  Not all that long ago crossing plum and apricot was thought impossible because no one had attempted it, today you can buy plumcots from the shops!  

 

Edit to add: I sent samples of these plants to the CSIRO who tested them and determined that they are true intergeneric strawberry raspberry hybrids.  The results can be seen here.