Heat tolerant, Heat Resistant, Hot Climate Tomato Varieties and breeding

[William Schlegel]

I am interested in climate change breeding and given last summer's heat wave which caused a great many of my tomatoes to pause setting fruit or to apparently set seed free fruit for a long time I thought I would look into maybe looking into heat tolerance.

Towards that I recently purchased a packet of Flamenco tomato a tomato descended from Silvery Fir Tree x Floridade from Lee Goodwin's J & L Gardens websites heat resistant section for growing in 2022.

I just did a search for others looked at several lists and here is what I found already in my collection.

Brandywine- just bought a packet because of Craig LeHoullier's top ten flavor list
Celebrity- have some segregating descendents not the actual hybrid.
Green Zebra
San Marzano- have some old seed
Stupice- old local standard here
Yellow Pear- haven't grown out in awhile!
Isis Candy- may be getting soon in a seed trade
Blue Ambrosia- the variety I got from Lee Goodwin's J & L gardens that is the source of many of the segregating lines in my collection including Exserted Tiger because of exserted stigmas.
Fourth of July Hybrid- wonder if this works more as a heat avoider ripening before it gets too hot? If so all the ultra early types would work for that.
Lucid Gem - Brad touts its heat tolerance on the wild boar farms seed page about it.

Wonder if I made any notes on here somewhere as to what did well last summer during that. 

[Diane Whitehead]

Are there any tomatoes from desert areas that can withstand both cold and heat?

I remember staying in one desert area in South Africa during spring.  The temperature was minus 8 celsius at night and plus 22 the next day.   I didn't check anyone's vegetable garden, though.

[William Schlegel]

I've wondered that as well. I feel like the ideal tomato here would be short season, cold tolerant, heat tolerant, and more! Can we have everything we want in the same tomato? That is part of why I chose the Flamenco I thought its Silvery Fir Tree parent might give it a chance here. When I was working in Boulder City Nevada the winter of 2012-2013 the back yard of my rental was bare soil, so we planted a garden and at the local garden center the tomato varieties were very different than any I had heard of. My neighbors there said that there is a very narrow window in the Las Vegas area for tomatoes and mine probably wouldn't produce. Then we took a job monitoring rangeland vegetation and left before we could find out for sure. 

I think it makes sense to cross very different or opposite tomatoes even though it is possible the results especially in early generations could be unremarkable.

[Steph S]

I  can vouch for Stupice and its descendants as being more heat tolerant than average.  Not surprised to see San Marzano listed either, and there are probably others selected for Italian growing conditions that tolerate heat and drought better than average.
Growing in a greenhouse, you are constantly trying to moderate extremes.  We get huge temperature swings and lots of experience with tomato stress from heat as well as cold.  There is UV stress too, if you have a week of overcast weather, the sun blazing out for a day can cause them some serious distress, even if the heat is vented.  If you get into a string of sunny days, they adapt to it, but the abrupt changes are challenging. 
One interesting fact is that night temperatures are important for fruit set.  If the nights are over 70F, they don't set, or set poorly.
Another rule of thumb is that tomato pollen is sterilized at temperatures over 95F.  So unless your flowers are getting some cooling - shade, breezes, etc - they don't have much hope of setting fruit in those conditions. 
Plant architecture is an important consideration, whether they will set well in spite of the heat.  I often look very closely at how the plants are structured, whether they put out a shade sucker early enough to protect the flowers, and whether the distance and orientation of the suckers vs the clusters is helpful or not. The same features also allow them to shelter flowers and fruit from cold.
Another interesting feature is the ability to set fruit even without pollination - adaptive or facultative parthenocarpy in plants that are normally seeded.  When pollen fails under heat stress, some plants will produce a reduced, seedless fruit instead.  And that's okay, when you need something to eat it is better than getting none at all.  I also like it that the plants are investing in animal attention, even if they won't get seeds.  So you keep watering them, and when it cools down they go right back to producing normal fruit again.

[William Schlegel]

That seed free fruit last year was weird!

[Jeremy Weiss]

I see a lot of talk here about heat/drought resistant tomatoes.  However I think it may also be useful, given that there ARE El Nino years, to talk about tomatoes that can handle both excessive heat and EXCESSIVE water i.e. ones that will do well if it rains constantly.

To that end, I think mention should be made of the tomato Nagaraclang (I think that was how it was spelled). This was a tomato I heard about about a decade ago (thought never successfully grew myself). Apparently, it was a black fruited tomato that hailed from the Philippine jungles and was notable for the fact that it's flowers would actually shed water in heavy rain (as opposed to most tomatoes, where heavy rain will destroy the flowers). That always sounded to me like a useful trait to have. 

[Nicolas]

That Nagaraclang Nagcarlang seems interesting.

Available at ARS GRIN :

PI 273445 / Nagcarlang
"Plant erect, stiff, to 49 inches high and 11 inches wide; fruit 1.6 by 2.5 inches, distorted shapes, purple, seven loculed, late maturing. A wild, cold-resistant type with protruding pistils which set fruit under rainy conditions. "

[Steph S]

There are some other interesting cases of adaptation to extremes in the Philippines.  I recall reading about Calamondin, a citrus fruit that ostensibly evolved to tolerate the darkness conditions associated with volcanic eruptions.

[William Schlegel]

https://doublehelixfarms.com/nagcarlang

So there is a commercial source also found a TGRS accession number so it is well represented in the gene banks.

[Jeremy Weiss]

https://doublehelixfarms.com/nagcarlang

So there is a commercial source also found a TGRS accession number so it is well represented in the gene banks.

Hmm, maybe THAT'S why it makes such a good and common houseplant (if you have ever seen those trees with the marble sized "oranges", THAT'S a calamondin)

[William Schlegel]

https://www.nativeseeds.org/products/tm005?_pos=1&_sid=d04b7d1f3&_ss=r

https://www.cell.com/current-biology/abstract/S0960-9822(24)01379-4

There is a new article out about heat tolerance in tomatoes. It isn't at all certain that they are related but Ciudad Victoria available from NSS is from the same region as the name of the cultivar in the article.

[Alex]

Brandywine, Green Zebra, San Marzano, Isis Candy, Blue Ambrosia - insufficient heat tolerance.
Yellow Pear - sufficient heat tolerance, but insufficient moisture tolerance.

there are probably others selected for Italian growing conditions that tolerate heat and drought better than average.

Some Italian tomatoes grow, but do not produce fruit except for Crovarese tomato.

[reed]

I am interested in climate change breeding and given last summer's heat wave which caused a great many of my tomatoes to pause setting fruit or to apparently set seed free fruit for a long time I thought I would look into maybe looking into heat tolerance.

I quoted from the original post because I am also very interested in breeding, or I think adapting is a better term, for dealing with climate change. In over sixty years of gardening in the same overall geographical location I have witnessed the effects changing weather patterns and thought for a while that trying to adapt to heat and drought was the logical response.

Heat and drought are certainly issues but far from the only ones. In recent years we have had a couple years where the whole month of August was cool and damp. This past season the whole month of June and 1/2 of July were like that, but then it turned to the heat and drought in last part of July, through September.

I've come to the conclusion that there is no one issue to focus on in attempting to prolong the ability to grow food except for one, and that is fast maturity. Well maybe two, (fast maturity) + (everything else collectively) and all at once. By reducing the days to harvest of everything I grow I hope to be able to get a harvest during hospitable periods between extremes.

The weather has always been unpredictable but fifty years ago it followed some reasonably dependable patterns. It doesn't do that anymore. But it didn't just change from one dependable pattern to another, instead it is in a state continuous and accelerating change resulting in more and more, often very brief, sometimes more prolonged, extremes. I think and hope that despite this there will continue to be windows of opportunity for gardening and focusing on short season maturity offers the best chance of taking advantage of them.

On tomatoes specifically the earliest in my garden are the descendants of the crossed pimpinellifolium that showed up several years ago. The shortest maturity time of the larger tomatoes were the Mr. Stripy and Hoosier Rose F1s that you did. Especially the Mr. Stripy endured the cool damp early summer very well and produced lots of tomatoes very rapidly when the weather shifted. It petered out a bit when the heat and drought intensified but no more so than any of the others in the garden, and it didn't completely stop. It just made fewer and smaller tomatoes until frost.

I can't keep track of the pedigrees, but I think somewhere back in those crosses, at least the Mr. Stripey one, is that old Russian tomato Jagodka. I wonder if that is where the shorter DTM might have come from.

I just thought, as far as my tomatoes that the crosses came from, they are the same tomatoes I've grown in the same ground for decades. They have been through all the weird weather that's happened in the last twenty years, sometimes producing great, sometimes not so good, but never none at all. Maybe they have developed some genetic or non-genetic adaptation.

[William Schlegel]

I think with climate change there is a lot of plant breeding to be done where we simply cross short season varieties developed for short season climates with varieties from different regions. Certainly with tomatoes but also just with crops in general. Short season varieties give resilience for getting a crop in a shorter window like Reed said. Though the professional tomato breeding work in my region ended about 1992 and those older northern varieties tend to be workhorse reds. So I think there is a real opportunity to create a much broader array of short season tomatoes which will be useful in the north but also potentially much further south where with them gardeners can take advantage of short windows. Heat and cold tolerance are just portions of what might be needed in some regions and even in some years of unsettled changing weather. Or basically: yep I agree Reed. Yep those two short season favorites Joseph found Jagodka and Brad are ancestors in the vast majority of my tomato crosses. Joseph crossed Hillbilly x Jagodka to make HX-9 which he registered as OSSI and then renamed Big Hill. I crossed Brad x Blue Gold and then later crossed both those crosses together. So most all of my tomatoes have those ancestors. Though since I've been crossing in more. I intend eventually to make crosses with all the collection tomatoes from Native Seed Search including that Ciudad Victoria and Punta Banda. I think desert southwest tomatoes probably have decent heat tolerance but may also have a bit of drought avoider short seasonality as well. Though I want a little south American genetics in the mix too. I think going forward I want some wild genes in the tomatoes I share. Wild edible palatable red currant tomatoes of south America have almost twice the genetic diversity of domestic tomatoes. I bet there are a lot of heat tolerance genes in there.

[Alex]

Wild edible palatable red currant tomatoes of south America have almost twice the genetic diversity of domestic tomatoes. I bet there are a lot of heat tolerance genes in there.

Not all of them are heat-resistant, for example, Rote Murmel is not. Also, in my climate, Solanum pimpinellifolium almost never sets fruit, with exception of some of its hybrids.
reed, pay attention to Texas wild cherry tomatoes, they are early, highly productive, lifespan is 8 months, heat resistance is high, they can survive in tropics except for May, June and half of July. They are able to set fruits in extreme heat, from which they themselves die. In addition, I observe a small percentage of parthenocarpy.