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.
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.
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.
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.
That seed free fruit last year was weird!
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.
That Nagaraclang Nagcarlang seems interesting.
Available at ARS GRIN :
PI 273445 / Nagcarlang (https://npgsweb.ars-grin.gov/gringlobal/accessiondetail?id=1205458)
"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. "
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.
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.
Quote from: William S. on 2022-01-07, 07:42:07 AM
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)
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.
Brandywine, Green Zebra, San Marzano, Isis Candy, Blue Ambrosia - insufficient heat tolerance.
Yellow Pear - sufficient heat tolerance, but insufficient moisture tolerance.
Quote from: Steph S on 2022-01-06, 07:35:13 PMthere 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.
Quote from: William Schlegel on 2022-01-06, 10:07:38 AMI 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.
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.
Quote from: William Schlegel on 2025-01-18, 04:59:42 PMWild 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.
This hot summer, Sara's tomato won for me. It easily survived the hottest period from May to mid-July and began to set fruit in mid-July. Of Texas wild cherry tomatoes, only 3% survived, while Sara's tomato did 100%.
That all makes sense because currant and cerasiforme tomato diversity is between accessions and not within them over a very broad geographical area. Most appear superficially similar but we can reasonably expect them to have some meaningful variation in important traits like degree of heat tolerance. So Sara's galapagose should be equatorial in origin and do well on Guam. Texas wild should probably have good heat tolerance for anyone North of Texas. Tomatoes from more arid regions probably have less tolerance to moist conditions and vice versa. I bet that here relatively modest heat tolerance is useful.
This explains a lot about how well the current tomatoes and their descendants do in my garden as well as all the different colors, sizes and flavors.
Reimer's seeds has some interesting potentially relevant lists of varieties.
https://www.reimerseeds.com/heat-tolerant-tomato
https://www.reimerseeds.com/humidity-tolerant-tomato
https://www.reimerseeds.com/drought-tolerant-tomato
The second link is for humidity tolerance useful for humid regions. The third link above is for drought tolerance which is relevant for arid regions.
Lee Goodwin has a list of just three heat tolerant tomatoes.
https://jandlgardens.com/xencart/index.php?main_page=index&cPath=105&zenid=0hd99u75ie0n8c97v1reiojuk3
Native Seed Search has only six seed bank accessions for tomato and a few others they have tested for gardening in the region. It would be interesting if someone from Tucson was a collaborator- I think interesting things could be done for Tucson or other desert southwest area gardeners with crosses with those six Native Seed Search accessions.
I think for Alex almost none of the above will be useful. Though maybe as something with a little bit of what is needed to cross the few survivors with? Like it sounds like Sara's could maybe be crossed with Texas wild there.
For my region almost any slight heat or drought tolerance might be useful. It sounds like Reed could use just a little bit, more heat resistance than me.
Quote from: William Schlegel on 2025-01-19, 08:53:48 AMLike it sounds like Sara's could maybe be crossed with Texas wild there.
You read my mind. Sara's tomatoes have better taste and better heat resistance, but they are small and not early, while Texas Wild Cherry Tomato is early, larger, but less tasty, less heat-resistant. Therefore, yes, a cross that inherited the best from these parents would be useful: large fruits, early, heat-resistant, tasty. Help from professionals is welcome, I will send seeds from survivors for crossing.
Quote from: William Schlegel on 2025-01-19, 08:53:48 AMI think for Alex almost none of the above will be useful.
I have tried some varieties from these lists. They either do not survive, or do not set fruit, or very little. In my case, only wild tomatoes and their hybrids are able to survive and produce fruit, and not all of them. Exceptions include Oregon Spring, Yellow Pear, but only March-April. Crovarese tomato is producing fruit now, which raises suspicions about its wild genetics.
Quote from: Alex on 2025-09-10, 02:10:12 PMYes, William, there are signs of S. lycopercicum in genes, but it is not listed anywhere. But it is important to understand how easily Sara's tomato can be crossed with S. lycopercicum. Sara's tomato is one of few tomatoes that can survive summer heat on Guam, and therefore is a potential source for crosses to improve heat tolerance. I plan to cross Sara's tomato with at least Texas wild cherry tomato in late November or December, because its heat survival rate is about 2% of population. And perhaps improve flavor, since Sara's tomato is tastier and does not require over-ripening like Texas one.
This year's autumn on Guam has been less rainy than last year, so tomatoes began setting fruit a month earlier than last year—in mid-October. Given favorable conditions for fruit set, I crossed wild Sara's tomato and Texas wild cherry tomato two weeks ago. Sara's tomato is being used as a pollen donor, as it produces very little fruits in my climate, making it difficult to use as a mother plant—chances of successful fruit set are several times lower—but it is well suited as a father plant. Fruit is currently setting. Fruits from F1 generation can be obtained approximately by the end of January, and fruits from F2 generation will be available in May. It's still too early to talk about a successful cross, but potential exists - several pollinated flowers produce visible fruits.
Quote from: Alex on 2025-01-19, 07:40:59 PMI will send seeds from survivors for crossing.
Nobody asked for seeds.
QuoteThe pollen of S. galapagense used to fertilize S. lycopersicum plants is able to affect the phenotype of seeds and fruits directly developed from the pollinated flowers, that is, these characters can present xenia (metaxenia in the case of fruits, more precisely).
"Interspecific xenia and metaxenia in seeds and fruits of tomato", 1 April 2013
When crossing Texas Wild Cherry Tomato (mother) with Sara's Tomato (father), I observed xenia and metaxenia. Fruits on mother plant bear such strong characteristics of father that they are a larger version of father's fruit, possessing its flavor and texture, yet are smaller in size than mother. As for xenia, seeds are not identical to mother, they are an enlarged copy of father. This allows me to conclude at a very early stage, without even growing F1, that cross was successful. I have very good taste and can distinguish between nuances of flavor, so I easily identified metaxenia by taste, confirming it by texture of fruit.
Fruits vary in number of seeds, with difference being nearly twofold. In my case, sweetness level varies with number of seeds due to difference in mother/father ratio in final fruit.
Of course, this is still a preliminary analysis, an error cannot be ruled out (although it is unlikely), and we will see more details in F1.
F1 generation begins to bloom, flowers are like father's, but twice as large.
IMG_20260107_163448 (1).jpg
Exciting times!
We're still in the grips of Winter here, so its nice to see some flowers
Good luck for 2026
Heterosis is evident. Leaves are three times larger than parent plants, and flowers are twice as large. Fruit sets successfully and increases in size very quickly. Given heterosis, I predict fruits will be twice as large, larger than mother plants. F1 hybrid plants are vigorous and bushy. Regarding heat resistance, at this stage, it can be assumed that it is inherited: hybrid has blue leaf trait, but this cannot be tested in winter.
Fruits 5 days later (one fruit was eaten by pests, the second is unknown):
IMG_20260112_124705 (1).jpg
Potential heat resistance:
IMG_20251228_153745.jpg
Comparison of flower size and shape:
IMG_20260113_144923 (1) (1).jpg
IMG_20260113_143756 (1) (1).jpg
Comparison of leaf size and shape:
IMG_20260113_144216 (2).jpg
F1 fruits are ripe. They vary in size and flavor. Fruit size is sometimes equal to mother's (mainly the first fruits), but generally slightly smaller. Flavor of fruits varies from mother to father. Softness of fruit matches father's, and attachment to sepals is the same as father's. Fertility is equal to mother's. I'm currently sowing seeds to obtain fruits of next generation in May. And perhaps in June, when weather is at its hottest, I'll conduct selection for heat tolerance.
Texas x Sara F1:
IMG_20260221_124125 (1).jpg
IMG_20260221_123932 (1) (1).jpg
IMG_20260221_124051 (1).jpg
While growing F2 generation of tomatoes, typhoon destroyed all leaves, leaving 90% of bushes bare. But a month later, 90% of tomato plants had recovered, giving me approximately 100-110 plants, enough to continue selection. Successful crossbreeding is confirmed by segregation of traits. Aphid infestation varies depending on color and shape of leaves. For example, green leaves are more susceptible to aphid infestation than blue ones. Currently flavor varies between flavors of both parents.
Photo shows an unripe orange-red F2 tomato plant:
IMG_20260523_134553.jpg
Photo shows a ripe orange-red F2 tomato plant:
IMG_20260530_170624.jpg
Productivity:
IMG_20260612_184609 (1).jpg
Color range ranges from orange-red, light red, to dark red. There are two-toned orange and red fruits (bicolor), and some with a white core. There is no obvious yellow color, but they become orange-red. Flavor, after more tests, is broader than that of parents and includes some rare plants with a super-sour taste. Fruit size varies between sizes of both parents; it is mostly medium, but one plant produces fruits larger than its parents. The most common shape of tomatoes is cherry, sometimes grape.
Based on these observations, it can be assumed that (hypotheses):
1) Texas wild cherry tomato two centuries ago could have been twice as large, or my Sara's tomato is not pure.
2) no obvious signs of S.Cheesmaniae, S.Pimpinellifolium were detected, but S.Galapagense, casting doubt on Sara's genetics. This is understandable, as most wild tomatoes on Galapagos Islands hybridize with each other, and Sara's tomato could very well be S.Cheesmaniae x S.Galapagense x S.Pimpinellifolium hybrid or even (the most likely to me) S.Cheesmaniae x S.Galapagense x S. lycopersicum var. cerasiforme hybrid.
Experience has shown that pure S. Galapagense cannot grow in my climate due to high humidity. Its hybrids do poorly, but produce only a few fruits before dying. In this case, some plants (no more than 3% of population) in F2 exhibit predominantly S. Galapagense traits, and they have already died.
carolyn137: "I was the one who introduced Sara's Galapagos and Amy named it and yes,it is a stable interspecies hybrid as Dr. Chatelet told me and he's at theTGRC in Davis, CA". That is, he only said that it was a stable interspecies cross, but he did not say that it was a S.Cheesmaniae x S.Pimpinellifolium hybrid.
Bicolor:
IMG_20260530_171010.jpg
Red:
IMG_20260530_170919.jpg
Productivity:
IMG_20260612_184700.jpg
8 kg/week (100 plants):
IMG_20260617_171409.jpg
Hi Alex,
I have a question,
The flowers of texas x sara are able to be fecondated at a temperature above of 35°C?
Hi Adrian,
This year we're cooler due to La Niña, with temperatures not reaching 35°C (95°F), but 32°C (90°F). In previous years, no tomatoes produced fruit in June; it was hotter. La Niña occurs here every 3-7 years. It's impossible to answer your question this year.
Regarding cracking, situation is as follows. In my case, orange color is due to S. galapagense genetics, which is naturally tough-skinned and resistant to cracking. It has been observed in practice that more orange tomatoes in F2 are less susceptible to cracking than those with a predominance of red. Therefore, in this particular case, cracking depends on fruit color.
Quote from: Alex on 2026-01-11, 07:39:20 PMGiven heterosis, I predict fruits will be twice as large, larger than mother plants.
This prediction did not come true for F1, but in F2 for 1% of population.
Quote from: Alex on 2026-02-17, 04:44:20 AMAnd perhaps in June, when weather is at its hottest, I'll conduct selection for heat tolerance.
Due to La Niña effect, which brought cooler temperatures and more rain, June was not the hottest month of summer.
Quote from: Alex on 2026-06-19, 06:26:36 AMFruit size varies between sizes of both parents; it is mostly medium, but one plant produces fruits larger than its parents.
Currently, two plants are producing fruit that are larger than crossed parents. One is dark red, tough-skinned, not sweet, and has a standard tomato flavor; the other is orange-red, soft-skinned, and sweet.
A question for experts. Since several genes and their combinations are responsible for large fruits, it's not easy to stabilize them. What's minimum number of F3 plants to plant from seeds, selected from F2 plants, that exhibit large fruits?
Here's what the F2 looked like when I crossed a beefsteak with a saladette.
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HX-hillbilly-X-Jagodka-2015-early-fruits.jpg
According to preliminary data, heat resistance is inherited; in my case, it's not manifested only in dwarf plants, whose leaves were constantly scorched throughout June. Further clarification is impossible during July and August, as a super typhoon is expected in two days, which will destroy everything.
IMG_20260704_152528.jpg
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Typhoon_Bavi_Track_Forecast_July_2_2026.jpeg
Unfortunately, typhoon destroyed almost all my plants, it was very strong and passed very close to my garden.
The following five lines were selected for the next generation of F3:
- bicolor cherry, standard tomato flavor
- red cherry, standard tomato flavor
- red cherry, sweet flavor
- large dark red cherry, tough-skinned, standard tomato flavor
- large orange-red cherry, soft-skinned, sweet
With temperatures currently around 90F during the day and 50 to 60 F at night I'm curious to see if any lines do or don't have difficulty setting fruit through the heat wave. It's possible with the nights still cool it won't make much difference.
I had a lot of days in the greenhouse with highs 90+ and lows in the 60's this July. I did have blossom drops but I had some sets too. Ended up with some crosses looking at the heat tolerance as a desired trait, but TBH it's impossible to account for the microclimate around a flower cluster with temperature reading in the shade. Still if they drop less, it's a sign of some sort we hope.
It was really noticeable, the flush of fruit growing when temperatures dropped to the 80's for a day. Also got a flush after a 90+ day when I gave them some lime slurry and a top up of an inch or two of potting mix. Maybe just the effect of keeping the soil cooler/ covering exposed roots?
This week our highs are not quite getting to 70, and that seems to have stalled the fruit growing action again.
We're having a weird year...