01 August 2010

How (and why) to breed tomatoes in your backyard

Since I had the chance to talk about breeding tomatoes on last week's episode of The Splendid Table, I thought I'd follow up with instructions on how to create your own tomato variety. It is really easy, I promise. If you start your own tomatoes from seed, you can breed your own tomato variety -- and you totally should because it is freaking cool. Any gardener knows the thrill of picking that first tomato you grew yourself. Picking the first tomato of a variety you bred yourself multiplies that thrill a hundred times. Then you get to name it. And share it with friends, or pass it on to your children.

So how do you do it? Well, the basic process is to pick two or more tomato varieties you like for whatever reasons and make them have sex with each other. That combines and scrambles their genes, so when you grow a bunch of their children and grandchildren, you get all different combinations of their traits, from which you get the pick the new tomato you like best.

For example: I garden in the north with a short growing season, so is it is very important to me that my tomatoes start producing early. But a lot of early tomatoes aren't very tasty. To remedy that, I could cross a very early tomato with a very delicious tomato. Their children (called the F1 generation) will all have exactly half of their genes from their early mother, and half their genes from their delicious father, and so will all be essentially the same, and usually roughly half-way between their parents. Save seeds from those plants, and you get the F2 generation (the grandchildren of the original parent varieties), each of which will be a random mix of the genes of the two original parents.(for a more detailed explanation of F1 and F2 generations, see my explanation here). If you grow enough plants of that generation, you'll hopefully find a individual or two which combines the best traits of both their parents: delicious fruits produced early. You'll also get some which combine the worst of both worlds -- late, bland fruit -- as well as crazy, unexpected stuff. Genetics is way more complex than I'm going to get into in this little explanation, so crosses don't always do what you expect.  Personally, I think that is half the fun. You plan the best you can, and then go with what pops out at you.

Once you find an individual plant in that F2 generation that you like, the next step is just to save seeds from that plant, and keep growing them out and picking your favorites for a few generations. Each year, you will see less and less variation in the plants you grow out from seed.  After a few years, when all your seedlings are looking, growing, and tasting pretty much the same, you've got your new variety. Give it a name, collect a bunch of seeds, and share them with friends and family. And, if you are like me, start dreaming up what you could combine it with next to make it even more delicious, or a different shape, or bigger or smaller or... the sky is the limit.

If you are a gardener, the whole process is pretty much stuff you know how to do already: Grow seeds, taste test, pick your favorites. The only think you need to learn how to make the two original varieties have sex to produce that first hybrid generation and start the whole ball rolling.

Here is how.
Tomato sex is all about the flower. Each flower has several layers: Green sepals that protect the developing bud, within them, yellow petals that attract pollinators. In the middle, forming a yellow cone, are the stamens, the male part of the flower that produces pollen (pollen = plant sperm) and in the very center surrounded by the stamens, the stigma (female). Sex happens and seeds are produced when pollen from the stamens gets on the stigma. Tomatoes are a bit odd in that they usually self pollinate -- they have sex with themselves. Usually, pollen from the anthers just falls down onto the stigma of the same flower, and hey presto, you get seeds that have just one individual as both their mother and father. Sometimes bees will carry pollen from one flower to another and mix things up, but it is fairly unusual.
In order to make two different tomato plants get together and make hybrid babies, you first need to prevent the mother of your hybrid babies from having sex with itself. So find a flower bud just about to open:
Using tweezers, carefully peal back the sepals and pull off the petals, to reveal the stamens. Those are the male parts of the flower, and they need to go. Hold the flower with one hand, and gently pinch and pull at the base of the stamens to peel them back to reveal the stigma hiding in the center of the flower.
This can be tricky. Tomato flowers are delicate, and it is easy to damage it in the process. Some varieties are easier to work with than others, so if one plant is giving you trouble, try a different one and see if it is any easier.

Once the stamens are out of the way, find a fully open flower from the other parent of your cross, and pull off one or two of its stamens.
You don't need to worry about damaging this flower -- all you need is the pollen, so you can rip it apart as much as you want. Once you've got a stamen, run your tweezer tip along the little groove on the inside.
 You'll see a little tiny bit of powdery, yellow pollen collect on your tweezer. (Yes, it is there in the picture -- click to enlarge if you can't see it.)

Gently dab this pollen onto the tip of the stigma of the first flower
(You can sing romatically or buzz like a bee as you do so, if you wish) and you have made your cross! Now just tie a string or something around it so you can find it again.
If you did everything right, the flower will develop into a tomato fruit, full of your F1 hybrid seeds. If you don't get fruit and seeds, you probably damaged the flower while pulling off the stamens. I usually do two or three flowers at a time to make sure I get at least one good one. When the fruit is ripe, collect your seeds, grow them out, and see what wonderful things you have created!


meemsnyc said...

Oh this is such an awesome idea, and seems so simple! I'll have to try this someday! Thanks!

Greensparrow said...

Meems, why someday? Why not today? It is SOOOO much fun...

Maia said...

Awesome! I just heard you on The Splendid Table and love to garden. Maybe next summer I will be growing some of my own varieties!

Maia said...

I mean maybe in a few summers, haha.

Greensparrow said...

I'm so glad you are going to give it a try, Maia. And even though it takes time to get the final product, You'll have cool, unique stuff right away.