As I look at the pad on which I’ve written the crosses I am attempting, it strikes me that I am just a bit crazy. When Patrina and I started the Dwarf Tomato Project back in 2004, she made less than 10 crosses and that set us off on years of work. If all of my 2020 crosses take (and as of today, it seems as though at least 18 of my 30 attempts appear to have resulted in a tomato, which may indicate success - but can’t be confirmed until later on….I will get to that below). However, about half of of what I am playing with this year is something new to me - crossing indeterminate heirlooms.

Part 1 of this series (of at least 2 parts) of blogs covered the parts of a tomato flower, the mechanics of doing a cross, and evidence that the cross worked, as evidenced by swelling of the ovary - the future tomato that hopefully contain the F1 hybrid seeds. (F1 means first filial generation, but don’t worry - I will keep the genetics basic and understandable).

Hopeful recent cross attempt on Perfect Harmony

I noted in part 1 that I liked to use as a female a variety that has a clear recessive gene expression. There is a useful reason for doing so. As an example, let’s discuss a cross between a regular leaf and a potato leaf variety. Regular leaf is the dominant leaf form, potato leaf is recessive. By using pollen from the regular leaf variety and applying to the emasculated flower on the potato leaf plant, it becomes possible to confirm the success of the cross much more quickly. Once the ovary swells, the tomato reaches full size and ripens, and seeds are saved and then the new hoped for hybrid seeds planted, if the seedlings are regular leaf, you can pop the champagne; you have clear evidence that the cross worked, as you ended up with regular leaf seedlings from a fruit plucked from a potato leaf plant. In the Dwarf Tomato Project, we took advantage of the recessive nature of the dwarf growth habit when compared with indeterminate growth. Pollen from indeterminate varieties was applied to flowers on dwarf varieties. Saved seed from the resulting tomato are grown, and if the seedlings are indeterminate, a successful cross was realized.

The following is a limited but useful list of traits, with dominant listed first, recessive next.

Indeterminate growth habit is dominant to determinate and dwarf growth habits
Regular leaf foliage is dominant to potato leaf foliage or carrot leaf foliage
Green leaf color is dominant to variegated and yellow leaf color
Small fruit is dominant to large fruit
Oblate or round fruit is dominant to heart shaped or paste shaped fruit
Yellow skin color is dominant to clear skin color
Red flesh is dominant to other tomato colors, such as yellow, green, orange, white and bicolor
Striped skin seems to have some partial dominance, interestingly
Regular colored flesh is dominant to deeper colored flesh, such as in Cherokee Purple
Regular skin color is dominant to anthocyanin skin color expression
I’ve yet to confirm dominance when crosses are made between non-red fleshed fruit - the relative dominance of yellow, orange, green, red/yellow swirled flesh, etc. I am sure that the outcomes of the dwarf tomato project will tell me a bit about this if I go back and review the data.
Microdwarf genetics seems to be a bit more complex; I crossed a micro with an indeterminate and the hybrid is determinate, a totally unexpected result!

The above list is by no means complete, but should provide enough information to be able to make some decisions about what crosses you may wish to make. You will note I didn’t discuss flavor. Because flavor is something you can’t “see”, it is one of the trickier traits to stabilize. It also means that breeding projects mean lots of tomato tastings. There isn’t anything to complain about with that activity!

Successful cross on Don’s Double Delight

Predicting the attributes of the hybrid

Using the trait list above, a good guess can be made as to what the hybrid will look like, as the hybrid will show all of the dominant traits exhibited by the two parents. Here’s an example - I crossed Cancelmo Family Heirloom with Dwarf Moby’s Cherry. Cancelmo is a regular leaf indeterminate with large pink hearts. Dwarf Moby’s Cherry is a regular leaf dwarf with round, large yellow saladette tomatoes. The dominant traits are indeterminate (Cancelmo), regular leaf (both parents), smaller fruit size (Moby’s Cherry), red flesh (Cancelmo), round (Moby’s Cherry), and yellow skin (Moby’s Cherry). Given that list, I would expect the hybrid - let’s call it Moby Cancelmo just for now - to be a regular leaf, indeterminate plant with medium small, round red tomatoes (pretty boring, I suppose).

What happens next - F2 and beyond

Now the fun begins. Save lots of seed from your new hybrid, because the more F2 plants that you grow out, the more interesting combinations you may find. This is where the recessive traits start to show up. This is also where the tool many of us learned in school - the Punnett Square - comes into play, but not for this discussion (it is the origin of the 3:1 ratio that starts to show itself with the growouts and various traits).

Let’s return to Moby Cancelmo. If you plant 25 seeds, you will note that roughly 75% will be indeterminate, 25% dwarf. You can grow some of the indeterminates to see what you get - there should be red, pink, pale and deep yellow colors (at least). You may get great variation in fruit size, cherry to large, and shape, round to heart. Flavors could be all over the map. The dwarf seedlings will show the same sort of variations and combinations. If you find something you like and save seeds from the fruit on just that particular plant, you are on your way to a new variety, but there are generations of work left to do. Each time you select for something you like and save seeds, you will approach more uniformity. It can often take to the 8th, 9th or 10th generation to produce a new, stable variety - an open pollinated variety - that will breed true each season from saved seeds.

Successful cross on Dwarf Speckled Heart

My crosses for 2020 - apparent successes - predicted attributes of the hybrid (there are often surprises, though!). (Some are listed as pink or red, as it depends upon the skin color of the yellow parent. If it is clear skin, hybrid will be pink; if yellow skin, red).

Cherokee Purple X Casey’s Pure Yellow - indeterminate regular leaf large red
Blue’s Bling X Little Lucky - indeterminate regular leaf medium red
Blue’s Bling X Brandywine - indeterminate regular leaf large pink
Blue’s Bling X Polish - indeterminate regular leaf large pink
Cancelmo Family Heirloom X Don’s Double Delight - indeterminate regular leaf large red, faint stripes
Cancelmo Family Heirloom X Green Giant - indeterminate regular leaf large pink
Cancelmo Family Heirloom X Lucky Cross - indeterminate regular leaf large red
Cherokee Chocolate X Stump of the World - indeterminate regular leaf large red
Ferris Wheel X Striped Sweetheart - indeterminate regular leaf medium red, faint stripes
Cherokee Green X Caitlin’s Lucky Stripe - indeterminate regular leaf medium small red, faint stripes
Blue’s Bling X Dwarf Mocha’s Cherry - indeterminate regular leaf small pink
Lillian’s Yellow Heirloom X Dwarf Mocha’s Cherry - indeterminate regular leaf small red
Lucky Cross X Dwarf Mocha’s Cherry - indeterminate regular leaf small red
Lillian’s Yellow Heirloom X Dwarf Speckled Heart - indeterminate regular leaf medium red, faint stripes
Lucky Cross X Dwarf Buddy’s Heart - indeterminate regular leaf medium red
Lillian’s Yellow Heirloom X Hearty selection - indeterminate regular leaf medium large red, faint stripes
Cancelmo Family Heirloom X Dwarf Moby’s Cherry - indeterminate regular leaf medium small red
Cherokee Purple X Lillian’s Yellow Heirloom - indeterminate regular leaf large red

Crosses attempted, results pending

Lucky Cross X Hearty selection
Blue’s Bling X Lucky Cross
Dwarf Sweet Sue X Dwarf Liz’s Teardrop
Cherokee Green X Gloria’s Treat
Don’s Double Delight X Dwarf Mocha’s Cherry
Green Giant X Perfect Harmony
Teensy Pink X Lillian’s Yellow Heirloom
Teensy Pink X Striped Sweetheart
Teensy Pink X Don’s Double Delight
Teensy Pink X Green Giant
Blue’s Bling X Scotty yellow potato leaf selection
Blue’s Bling X Teensy Pink

What’s next?

I am going to leave this as a two part blog at the moment. As the tomatoes resulting from my crosses ripen I will save seeds, and hopefully plant some. The first observation of leaf shape will confirm that the cross took. If time allows, I will grow the new hybrids, report on the fruit (and compare to my predictions), then save seeds. I’d love to then see if anyone wants to play along and grow out some saved seeds to start to explore the possibilities going forward. We may also find that some of the new hybrids are pretty great varieties. Lots of fun lies ahead, that’s for sure.

Successful cross (and my wayward finger) on Polish