Solanum is full of a bunch of edible species.
"Eggplants" - Solanum aethiopicum, Solanum uporo, Solanum melongena - and other species.
There's also the whole clade with Naranjilla (Solanum quitoense), and Cocona (Solanum sessiliflorum).
Solanum lycocarpum - the wolf apple. Kangaroo apples - Solanum laciniatum and Solanum aviculare.
These are all some cool species, clades and the like.
But, I'd like to focus on Solanum lycopersicum, and it's relatives.
S. pimpinellifolium, S. cheesmaniae and S. galapagense. These would probably be species that a lot of people are aware of. That last ones a bit less known. And people sometimes present hybrids as the true species.
There's also, plenty of other species in the same clade as these. Sure, Pepinos - S. muricatum, probably belong in this clade.
But, they probably would need a few bridges to cross into tomatoes.
There's S. chmielewskii, S. peruvianum, S. arcanum, S. chilense, S. neorickii, S. corneliomulleri, S. huaylasense, S. habrochaites and S. pennellii
S. lycopersicoides and some others also would probably fit into the clade. There's also subsections and whatever.
S. neorickii, S. chmielewskii, S. arcanum, S. habrochaites, S. pennellii all seem to cross into common tomatoes without huge problems.
The main issue, is that the cross only goes one way.
Many of these wild species, are Self Incompatible. This means that they only accept pollen from other plants / can't be too genetically alike to form offspring.
Tomatillos tend to act the same way.
S. pimpinellifolium, S. cheesmaniae and S. galapagense are all self compatible for the most part.
The SI (Self Incompatible) species, also have their female organs highly exposed.
SC (Self Compatible) species, can sometimes have a slightly exserted female organ exposed - but it's usually not to any high extent.
It appears that the Self Compatible species, need to be the mother in many crosses with these wild species. It's very possible that the other species that have their female organs exposed, developed barriers to prevent other species from crossing over into them too much.
This does make hybrids a bit rare in some cases.
Generally the offspring is huge or very stunted. In one case a population absorbs beneficial genes and things go back to normal.
Many of these species are just used to bring over resistant genes.
Talks elsewhere, have been interesting though.
There's S. habrochaites accessions which have leaves that act as insecticides, efficient ones. And there's accessions which are hardy down to around 25F - they would still probably die back.
Capsicum flexuosum and some Physalis species are also hardy to similar regards. Same family as Solanum.
They also share the same issue that many backcrosses would be needed to carry over that hardiness.
But there's more. Different species also intake moisture from the air, and can survive almost entirely off that. Some species are very drought tolerant.
Some species have traits which would compliment each other in certain climates.
There's also species which impart new color / flavor genes, and added shelf life.
Did I forget to mention citronella scented or other scented sorts of leaves?
How about the fact that most purple tomatoes came from mixes of wild species, bred into tomatoes?
Also, try looking at some wild species flowers. They're larger than standard flowers - can rise up past the foliage, and have some orange markings or other traits on them.
Now, there is the issue of one gender not carrying over certain traits because it's not a mother / father. But, once you cross a species over into a high enough amount, it can typically begin to be able to cross into its mother father species or whatever.
So, its an issue but it can be worked against.
S. peruvianum and some other species are hard to cross into tomatoes.
There's also accessions of S. peruvianum which cross well into domestic tomatoes or ones which are self incompatible. And they'll still cross with other S. peruvianum which will not cross into tomatoes without embryo rescue.
The same goes for some other species in the clade.
Really messes with people's idea of what makes a species, a species.
The Self Incompatible trait and exserted traits have been picking up some traction in some circles.
These ensure that possible resistant traits and mutations are passed around / along a population of tomatoes.
It's also possible to bring along the cold hardy traits or make leaves and varieties which do better in certain climates.
Tomatoes are tropical plants being grown everywhere else.
So, different leaf types, root types and whatnot. Those can help prevent the issues that cause diseases in the first place.
Mission Mountain Sunrise, Exserted Tiger, Exserted Orange, Orange Hill and Big Hill are some known exserted varieties.
Some, or many have a lot of wild genes in them.





Exserted Tiger would be the fruit with stripes on it.
It's not very exserted. The other plant that I'm growing, is.
These tend to have the female organ sticking out, before the flower even first opens. So. It also makes crossing a lot easier.
The main issue may be having neighbors contaminating non exserted populations with things.
I've found that species with a ton of different species mixed into them, can tend to outcross to further semi related species sometimes. I wouldn't say that a Kangaroo apple cross or Pepino cross is out of the question with these things at some point.
Anyways, I noticed people mentioning that tomatoes are tropical fruits.
I also saw like one mention of Solanum peruvianum.
Most of the breeders who I know are using these for breeding, live in zones 4 - 7 for the most part. They usually can't successfully grow some species or they lose genes when crossing things because they're forced into one more adapted parents cycle or life span / etc.
Dunno if anyone here is interested in this.
I look at the exserted flowers as a "Oh I can do lazy crosses and just select for exserted offspring along with whatever traits I want."
Tomatoes also tend to give out more flowers than peppers or germinate faster - less of a hassle to breed with in my opinion.
I can go on a bit more if others are interested.