Perennial Cold Temperate Tomatoes
Hard graft
Every so often, I pick up the idea of perennial cold temperate tomatoes and toy with it before dropping it again. It’s like an itch in my brain that won’t go away.
Tomatoes are somewhat frustrating to me because, in general, vegetable growers pour so much energy into cultivating a tropical perennial as an annual. There’s a reason why they’re fussy; they didn’t evolve for cold temperate climates! Every climate that drops below 10°C for more than a day or two is a hostile environment for your friendly tomato.
Whole cultural cuisines are based on this humble fruit, and though there are some lesser known alternatives (hawthorn ketchup, anyone?), you’ll have very poor odds at sating the baying masses.
So what can we do about this?
I have a mad cap idea that might bear fruit. Maybe someone will run with this seed, let’s see.
How to Create a Perennial Cold Temperate Tomato
Step 1: Grafting
We find a cold hardy root stock of something in the Nightshade family (Solanaceae) and graft the hardiest tomato cultivar to it.
Yes, that’s right. I am not out of my mind, this kind of thing is done all the time. A fellow on permies.com talks about what species in the Rosaceae family can be grafted to a Hawthorn (which is in the Craetagus genus and falls within the Rosaceae family too). Growers do this a lot because choosing a hardier root stock confers advantages to the more delicate fruiting scion. The root stock may be better able to tolerate wet conditions, for example.
I’m proposing the same mechanism here. The tomato is known as Solanum lycopersicum. It is in the Solanum genus, and falls within the Solanaceae family. What I’m proposing is to find the hardiest tomato cultivar - likely something from Siberian or Scandinavian genetic heritage - and graft the tomato onto a cold hardy member of the Nightshade family.
Still think I’m mad? Well, a few researchers have attempted this intergeneric graft already. These guys grafted tomato scions to Lycium barbarum (known to common folk as wolfberry or goji berry) root stock. They were not looking for perenniality but salt tolerance, but the concept is the same.
In fact, Lycium barbarum is commonly grown as a hedge in the UK. It’s a woody perennial shrub that bears attractive nutritious red fruit that’s recently gained popularity as a super food. It can tolerate temperatures down to -15°C and coastal exposure.
Next to its cousin, the tomato is a weedy little push over.
Step 2: Children of the Graft
Back to our paper, the authors found that their grafted tomatoes were able to bear fruit in previously intolerable saline soil - so if you have some salty soil that you really want to grow tomatoes in, here’s your cue.
More importantly, for our perennial cold temperate tomato project, the paper cites another particularly amazing paper. Researchers here grafted a tomato scion to the closely related Lycium chinense rootstock. They found that micro RNA from the root stock ended up in within the genetic structure of the tomato.
I’ll say it again, they found some genetic material from the rootstock within the tomato.
My understanding of biology is quite limited, so I’ll just quote from the Wikipedia article:
miRNAs are considered to be key regulators of many developmental, homeostatic, and immune processes in plants. Their roles in plant development include shoot apical meristem development, leaf growth, flower formation, seed production, or root expansion. In addition, they play a complex role in responses to various abiotic stresses comprising heat stress, low-temperature stress, drought stress, light stress, or gamma radiation exposure.
I emphasised “low-temperature stress” and “light stress” because I believe these are probably the two greatest hindrances to perenniality in most plants. Missing of course is some type of “water stress” but I would bet that if microRNA regulates all these other responses it will have a key role to play in a tomatoes ability to cope with pounding rain.
Zooming out from tomato specifics, people have known intuitively and later proved scientifically that grafting distantly related plants together causes a mixture of their genetic material. As far back as Ivan Michurin, a famous Soviet plant breeder, who pioneered amazing integeneric hybrids such as the Sorbopyrus Titan (Aronia, Sorbus, Malus and Pyrus hybrid). I am only tip toeing in their giant foot steps.
My intuition, which I’m delighted to see has a scientific basis is to allow the tomato-goji tree graft to set fruit, and grow some tomato plants from the seeds. These children will have a small proportion of genetic material from the much hardier goji tree. We can grow these children along side the original tomato seeds to compare vigour and environment adaptation, and my bet is that they will out perform their unadulterated cousins.
Once these children are sufficiently large, we graft them back onto the goji tree. The seeds in the fruit of these next generation tomatoes should contain even more genetics from the hardier goji cousin, and can be grown next to the original tomatoes to again compare vigour.
And so on and so forth. We keep grafting the child tomato back onto the goji tree, testing for hardiness and using the original tomato seeds as a control. My hunch is that these tomatoes should become increasingly hardy as they take on more and more of the goji tree genetic material.
The true test is of course to see if it survives through any cold temperate climate winter.
Step 3: Stabilisation
If our mad cap scheme has worked, then we’ll want to stabilise our new hardy tomato. All I mean is to grow this new hardy tomato from seed without the grafting-to-goji step.
Final Thoughts
I’m sure someone will shout if they think that what I propose is somehow impossible, but I’ll probably say something like “try it first!”. The beauty of this scheme is that it hews quite close to reality anyway - some researchers have actually performed the graft and produced tomato fruit too. All I propose is a cyclical loop, with an eye for perenniality/hardiness.
It might be easier than integeneric hybridisation too, because we can bypass pollen incompatibility - we’re basically forcing a frankenplant. It’s strange how plants are fine with this but animals are not.
If my plan works, then will this new tomato plant really be a true tomato? What’s a species anyway? Instead of Solanum lycopersicum it might be something like Solanum barbarum.
Until next time.
Sounds like an interesting project. Have you done much grafting before? Getting a quality blade and maintaining it (or using disposable blades) is key. Grafting very young seedlings generally works better for mentor grafting (they seem to incorporate RNA/DNA/organelles from the root stock more readily). If you can time the grafting to happen in late summer/autumn then the young seedlings could be exposed to cold stress as they grow, which could provide extra selective pressure.
Cool, one thing i thought in my itch about the cold hardy perennial tomatoes was to do a similar breeding method between tomatoes and potatoes, since potatoes can be left under the ground and resprout also you could have a double crop, the technique was based on a different breeding also using grafting, basically whenever you graft two plants not only is genetic information shared between the two but at the graft point almost all genetic information is shared meaning that if you then take the small thin graft callous and grow it into a new plant it will be tomato genes+potato genes together, potato tubers left in the ground aren't that cold hardy though its all a matter of mulch but this technique of taking the grafting point could be used with tomatoes and goji berries too, you would need more breeding to make palatable fruits and cold hardiness but that could take a lot less time than miRNA transfer, my grafts never succeded but i have a big goji berry plant that wanted to reduce, (its not productive grows mostly leaves and stems and spreads asexually) and i might try grafting some tomatoes on it this year.
I dont want to write too much but here you can look somatic hybridization of tomatoes and potatoes (not great) not the same as hybridization by grafting but produces alnost the same result a polyploid plant with both genes
https://www.researchgate.net/publication/250680170_Somatic_hybrid_plants_of_potato_and_tomato_regenerated_from_fused_protoplasts
And here an overview of hybridization by grafting, there are more sources you can find yourself though
https://www.sciencedirect.com/science/article/abs/pii/S0065266006560031
Here hybrid between N. Tabacum N.Glauca to create new specie N.Tabauca: https://www.nature.com/articles/nbt.3010
Anyway as you can see it might be possible to create a tomatoish plant that sheds its leaves in winter and regrowing in spring possibly allowing for large tomato plants to be ready and growing as soon as spring starts, you could do this with the cold hardy pepper capsicum flexuosum as well