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

[Alex]

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%.

[William Schlegel]

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.

[reed]

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.

[William Schlegel]

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.

[Alex]

Like 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.

[Alex]

I 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.

[Alex]

Yes, 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.

I will send seeds from survivors for crossing.

Nobody asked for seeds.

[Alex]

The 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.

[Alex]

F1 generation begins to bloom, flowers are like father's, but twice as large.

[Tim DH]

Exciting times!
We're still in the grips of Winter here, so its nice to see some flowers
Good luck for 2026

[Alex]

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.

[Alex]

Fruits 5 days later (one fruit was eaten by pests, the second is unknown):

Potential heat resistance:

[Alex]

Comparison of flower size and shape:


Comparison of leaf size and shape:

[Alex]

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.

[Alex]

Texas x Sara F1: