Frost and Cold Tolerant Tomato Breeding including epigenetic and regular genetic

[Joseph Lofthouse]

Ah.... The confounding effects. Always present in plant breeding. Did that plant thrive because it is resistant to blight? Or because it didn't get infected? Is that rye plant 25% taller than the rest because of genetics? Or did a vole die under it's roots, thus providing an extra boost of nitrogen?

Do short stubby tomato seedlings survive frost because they are protected by taller plants? Or because they are closer to the warmth of the ground? Or both?

My general belief is that I can't understand, nor control for, the confounding effects, so I focus on bulk-selection over decades, as my go-to plant breeding strategy.

[Steph S]

LOL vole.   
Worth mentioning as an aside, that my tall BT emmer from last year is tall, while the short emmer is short, so that at least was a genetic thing.
OTOH I really don't know why I have patchy survivorship among the grains - did frost get through my row cover tatters?  Was rain penetration uneven?  Did wireworms eat the roots?  Oh well...  We're going with the survivors, whether they're "the lucky" or had some genetic edge.

I stopped starting tomatoes too early for a couple of years.  I was tired of seeing first clusters not set for the effort, but then starting late means they get the scorching in July and it's too late to be setting when it gets hot.  I need my tomatoes to set up when it's cool and ripen up when it's too hot to be setting.
So this year it was early again.
Those seedlings got all the epigenetic prompts they need for the season, that's for sure.
It's a crapshoot starting early, because the weather's so unpredictable.  But even so, I think I'm ahead of the game with fruit set and growing before the end of June.  If we hit some heat bumps I could, technically, let them keep on going longer and set up again when it cools off.   I probably won't do that because I prefer to limit the time I spend growing our tomatoes.  If we hit some cold bumps - I'm not a bit worried about that.   These plants spent what, nearly a month with close to freezing temperatures at night and quite a few days not over 60 F or an hour or two at best above 60, while sitting in beer cups. 
The plants I put outside weeks earlier than I would normally dare, are shrugging off the 'nearly frosty' nights.  It's true we have not had a white one here in spite of the threats this year.  Could still happen but...   no I'm not worried.  Minimal protection is enough, because all their epigenetic resistance has been activated well and truly.

I am deeply curious about the work you guys have done, and once I actually finish a couple projects I want to open up some space to try out the OPs you like and the lines you've created.  I would treat them the way I treat mine, which is as much as I can do to bring out the stress tolerance genetics.   Would also be happy to throw you some seeds of mine  to see how the tomatoes that we've trained to the environment here also perform in your trials.

I do think there's a big difference between wet cold and dry cold, also the difference between a cold night with a hot day, and the long bouts of sunless cold days and nights that we get here.  It's no surprise to me that people in different places have different favorites, because they suit that environment and are at their best.
Heat stress is as big a factor as cold stress, if not more, when it comes to tomatoes.   And the response to variable extremes.  Every year I see my plants wilt and freak out when it suddenly becomes hot and sunny with high UV after a long stretch of grey and cold.   Give them a week of sunny weather and they've adapted to that.  But there's no question in my mind, it's not easy for a plant to be ready for both.

I know there are genetics in some plants at least, that respond to all kinds of stress.  The chemistry for stress tolerance just isn't there in tomatoes in the same way.

[William Schlegel]

I wonder though, talking improved protocol, say instead of throwing a whole flat out in the cold, maybe smaller flats or just the outer part of one of those flats with holes so there are less microsites and the physics is more similar for the individual seedlings.

This spring when I was done with my interspecies hybrid search on some flats I tossed them out into the cold and it was definitely the understory in the center of the flat that survived the longest. I think that was just physics.

Another improvement might be to follow a suggestion from Darrel Jones if I recall it correctly. He stressed a genetic difference between cold and frost tolerance as two different goals and suggested refrigeration for cold. He said non cold tolerant seedlings will turn to mush. Cold tolerant will be fine. So maybe just a little community pot in the fridge for a week for say a segregating population? Also maybe some test pots of seedlings of parent or potential parent varieties.

I suspect that Black Strawberry, Lizzano F1, and a number of currant tomatoes are cold tolerant given this weekend's fruit set findings. Kind of surprised there aren't a few more. Might be that they had some transplanting advantage and some cold tolerance. Fridge test would be interesting on them.

[Nicolas]

Some cold hardiness in S. pennellii

A calcium-dependent protein kinase gene SpCPK33 from Solanum pennellii associated with increased cold tolerance in tomato

[William Schlegel]

Accession LA 0716 penellii in your article Nicollas. I wonder how widespread this protein kinase gene is in penellii? If the accessions, we have already been using in Joseph's promiscuous project have it or not.

There is so much tomato diversity locked up in the genebanks but there are barriers both to accessing it and to using it because it is a many generations tomato breeding effort to get these things introgressed into palatable lines.

[Nicolas]

I wonder too. LA716 is usually used because it is SC so easier to study i guess. It has an impressive range of resistances but again maybe just because it is more studied than other accessions of this species.

For the accessibility of interesting germplasms, we should definitely try to do something between us on this board, because we have access to different levels to different genebanks around the world.

[Steph S]

I wonder if this particular protein kinase activity might affect the palatability of the fruit (I did not read the full article for details).

Some of the common frost tolerance mechanisms in other plants involve the accumulation of polyamines like 'putrescine'.  Not a flavor enhancement, I would imagine.

Tomato wild relatives are reported to use the same mechanism for drought tolerance, and probably do so for frost tolerance as well:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5809557/

"..one of the strategies used by S. pennellii against osmotic stress induced by salinity22 was the avoidance of leaf dehydration by osmotic adjustment, inducing high accumulation of solutes during the stress period23,24. Interestingly, this adaptation strategy appeared earlier in the time-course of drought response of S. pennellii than in cultivated tomato. The tomato wild species accumulated organic solutes as sugars and the diamine putrescine if inorganic solutes were not sufficient to reduce the osmotic potential"

Maybe that would not be an issue for frost tolerance in young seedlings, but the question in my mind is, would this mechanism kick in later in the season in response to drought or fall frosts when tomatoes are ripening, and would the same solutes accumulate and affect flavor in the fruit?  Maybe not if it has a high brix ie easily accumulates enough sugars for the purpose.  Or perhaps the same mechanisms do not apply to fruit?

Ever since I read about this some years ago, I've wondered if 'putrescine' might have been a flavor in that horrible pimp I tasted (and spit out!).    maybe a dash of cadaverine too..   As they are named for a reason.

OTOH there may well be other frost tolerance mechanisms in the pennelli or others, that would be more compatible with developing palatable fruit.

[William Schlegel]

Interesting: I got the S. pimpinillifolium Mexico Midget to test its inclusion on a top 10 list for flavor. First one I tasted was when the weather was still quite cold- a spitter. Later it tasted fine. I don't know about top ten, but a good tomato. So it is very possible that cold grown tomatoes of fine flavor period may just be a difficult row to hoe. I would be very excited to be able to reliably plant my tomatoes a month earlier without protection though!

[Steph S]

To be fair, it is really common for tomatoes to produce less than optimal fruit in cold weather.  The enzymes involved in synthesizing flavor compounds as the fruit ripens are non functional at colder temperatures.  This is why tomatoes shouldn't be kept in a refrigerator.  A lot of varieties also produce bad textures in their early/cold set fruit - nasty, mealy as well as low taste. Not to mention catfacing. There are some varieties that do better than others re fruit quality in the cold, so the genetics is there to select something that works.
We also reach a point in the fall when the remaining tomatoes are not going to ripen or produce a nice fruit if left on the vine.  The solution is to bring them in and bag them and let them ripen at room temperature.  That might improve your fruit quality in the spring as well, if you end up with a line that tolerates the frost and sets well but aren't up to par for taste.  You could pick at breaker and try ripening them under indoor conditions instead.

[Steph S]

Just wanted to add:  I had to do some reading to refresh my memory about other chemistry of frost tolerance.  Not everything is putrescine! 

some notes:
https://pubmed.ncbi.nlm.nih.gov/34605046/
Cytosolic proline in basal freezing tolerance 

glycine betaine aka tremethylglycine
also an amino acid derivative, " It has a sweet and umami taste. "
https://en.wikipedia.org/wiki/Trimethylglycine

Discovered in sugar beets, but occurs naturally in many others:  wheat, spinach, beets etc are natural accumulators of gly betaine under stress, and it plays an important role in cold tolerance/frost tolerance.
Tomato unfortunately is a non accumulator.

The enzyme choline oxidase determines whether glycine betaine accumulates or not.
https://onlinelibrary.wiley.com/doi/10.1111/j.1365-313X.2004.02237.

You can actually spray glycine betaine on tomato plants to induce cold tolerance or other stress tolerance.
Sugar beets are easy to grow.  I thought about making a home product for that but basic desire for the plant to just do it for itself, ahem.  Well I haven't been motivated enough to do it yet.  But it might be fun to spray those late fruits or early fruit under cold stress and see if it keeps em going sweet and umami.

-------------------
Here's something useful about pennellii.  I couldn't find anything open about the protein kinase that Nicolas ref'd.  But there is genetic variation in the accessions of pennellii for stress tolerance acylsugars (sweet and umami, perchance?)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6961621/

Candidate Gene Networks for Acylsugar Metabolism and Plant Defense in Wild Tomato Solanum pennellii[OPEN]

[AndrewB]

https://wildmountainseeds.com/product/heirloom-survivors-grex/

[Cathy A]

Interesting: I got the S. pimpinillifolium Mexico Midget to test its inclusion on a top 10 list for flavor. First one I tasted was when the weather was still quite cold- a spitter. Later it tasted fine. I don't know about top ten, but a good tomato. So it is very possible that cold grown tomatoes of fine flavor period may just be a difficult row to hoe. I would be very excited to be able to reliably plant my tomatoes a month earlier without protection though!

Just getting tomatoes that would grow well in cool weather and pruduce tasty fruit promptly when warm weather arrives would be a big gain. Especially if the fruit picked at the end of the season in cool weather ripened well indoors.

Steph's thoughts are very interesting.

[William Schlegel]

Frost damage is a bit nonsensical. I bet the center tomato in this image has higher nitrogen content than the tomatoes to its left and right. I thought R18 had some frost tolerance last fall. This one though is the two current tomato crosses I made crossed to each other.

[reed]

I don't know that I've ever seen much frost tolerance in the fall. Sometimes just the tips of the plants get hit but it's pretty uniform across all of them. Frost tolerance on early volunteers seems pretty common, especially while they are still very small.

Well, I take that back about the fall, just last year I think it was some volunteers that spouted very late, like in September or maybe even it was October all in the apparently same conditions but one shrugged off a heavy frost while the others croaked. Like in you photo they were also quite close together. The one that survived and those that didn't were also much larger than tiny seedlings when it happened. At that time of year though, it wasn't long until a real freeze took that one out too. 

[reed]

.... So it is very possible that cold grown tomatoes of fine flavor period may just be a difficult row to hoe. I would be very excited to be able to reliably plant my tomatoes a month earlier without protection though!

Just noticed this earlier post. I agree good tasting tomatoes in cool weather may be difficult. I base that on the fact that in my garden that ripen in fall after the weather has started to cool do not taste nearly as good as those that mature earlier. It gets hot enough, fast enough here that ripening in cool weather early in the season isn't generally a factor.

In spring I can plant them earlier maybe even find some early season frost tolerance but from what I've seen it might not help all that much. Seems to me that staying alive is about all they might do; real growth doesn't take off until consistent warmer weather arrives.

I think that's an area where genetics and breeding might make a difference, still I wouldn't expect flavorful ripe tomatoes until it got warmer, but if green ones of some size were already nice size on the vines and ready to ripen a harvest might be achieved sooner. 

I think heat is a player in good flavor of lots of things. Strawberries in the hot sun, melons in the hot sun, pretty much any sweet, tasty thing is better if it ripens with heat. Other things like brassica, green beans and so on are just the opposite.