Cross Pollination

Hey all! I've been looking into cross-pollination between different garden plants. Obviously, all cultivars within a given species can and often do (though some are more or less prone than others) cross-pollinate with other cultivars of the same species. Moreover, species within certain genera and even (perhaps) certain families can cross-pollinate with other species of the same genera and/or family. However, trying to find which genera/families have inter-species pollination is difficult and much information is contradictory. Thus, I bring you a list of genera and families; my question is, in each genera/family, can the species within it cross-pollinate?

Families:
Amaranthaceae
Alliaceae
Solanaceae
Leguminosae
Cucurbitaceae
Brassicacea
Umbelliferae


Genera:
Solanum
Brassica
Allium
Cucurbita
Cucumis
Arachis
Lactuca
Mentha
Salvia
Ocimum
Helianthus
Rubus
Vicia
Phaseolus
Vigna
Claytonia
Origanum
Chenopodium

Short answer - it depends.  But most gardeners don't worry about it because people have been saving seeds in 'imperfect' conditions for millennia without any detriment.  


Long answer - are you wanting to maintain (aka, limit genetic variation) a variety or create a variety that grows well in your environment and improves with flavour each year (increase genetic variation)?

Most gardeners don't worry about interbreeding much when saving seeds.  They aren't growing for a mechanical harvest where every tomato has to come ripe within a day or two of each other.  They are growing for flavour and vitality.  So having more genetic variation helps.  

Most studies on plant interbreeding are done in a commercial setting so the bug population is generally quite low.  Diverse home gardens are more likely to have diverse pollinator populations so interbreeding can be higher than the studies.  But you can also limit polination by planting something tall between the different varieties.  

The best book on the topic is Breed your own vegetables by Deppe.  It includes tables and pollination rates on most common and uncommon veg. as well as the advantages and disadvantages of maintaining varieties and how to create new varieties that thrive in your garden.  

I think of biology as fuzzy, and far removed from the black/white labels that reductionist scientists want to put on things. Thus, any article you read that depends on black/white thinking might contradict another article that relies on a different interpretation of black/white, or that approaches the topic holistically.

In 15 years of growing moschata squash close to other squash, I only found one natural hybrid with another species. But I found a number of between-species hybrids among the argyrosperma squash. And every variety within a species has a different susceptibility to inter-species crossing. I haven't found an interspecies cross with pepo as the mother.

I don't worry about it, cause things with huge genetic differences almost never cross.  The crosses often carry sterility, or lack vigor, so they self-eliminate. If they do cross, then I might find something interesting.

These resources might help if you're trying to figure out the probability of any given interspecific cross working:

https://taux.evolseq.net/CCDB_web -- Plants with the same chromosome count are more likely to successfully cross/produce fertile offspring. This site also lists some of the known interspecific hybrids within genii (look for the [genus] x [name] format).

https://www.onezoom.org/ -- You can use this to eyeball how closely related two particular species/genii are. There's surprising stuff to discover; for example, according to this chart, loquats are much more closely related to pears than apples are. The more closely related, the more likely a cross works.

For assessing the existing data on crosses, going on Google scholar and trying "[genus] hybrid" and "[genus] interspecific cross" will often turn up info.

The families are a little broad to address here, but there are some notable hybrids in most of the genera you asked about:

Solanum - lycopersicum, cheesmaniae, pennelli, habrochaites, pimpinellifolium, etc have complicated reproductive compatibility with one another
Brassica - https://en.wikipedia.org/wiki/Triangle_of_U
Allium - https://www.row7seeds.com/products/sweet-garleek claims to be a garlic-leek hybrid
Cucurbita - tetsukabuto is a well-known moschata x maxima hybrid with partial sterility
Cucumis - hybridization with wild relatives has been used to introduce disease resistance
Arachis - hybridization with wild relatives has been used to introduce disease resistance
Lactuca - cultivated lettuce occasionally crosses with its wild relatives
Mentha - peppermint is a notable (sterile) hybrid of spearmint and watermint
Salvia - white sage naturally hybridizes with black sage and cleveland sage
Ocimum - basilicum has notably been crossed with kilimandscharicum in recent years
Helianthus - annuus crosses with argophyllus
Rubus - basically every notable plant in this genus is a hybrid
Vicia - favas have been artificially crossed with some vetches in experimental settings
Phaseolus - some hybridization between coccineus and vulgaris
Vigna - some compatibility between radiata, mungo, umbellata and angularis
Claytonia - apparently, claytonia has significant variation in chromosome count among its species, which makes hybridization difficult
Origanum - O. x majoricum
Chenopodium - quinoa crosses with its wild relatives

The vast majority of viable interspecific hybrids have not yet been recorded.