If you thumb through a catalog that offers a wide selection of open-pollinated (OP) tomato varieties, you’ll notice that many of them are named after individual people. The listings probably include varieties like Dr. Wyche’s Yellow, Dr. Neal, Aunt Ruby’s German Green, Aunt Ginny’s Purple, and Crnkovic Yugoslavian. All of these are considered family heirlooms, presumably named after the family member who championed them. The unusual names and the history they represent-whether that history is known or not-are part of the lure of heirloom tomatoes.
What makes these plants truly special is that you can create your very own heirloom varieties. If you have the time and the space, breeding your own tomato variety-with the traits and taste that appeal to you-can be quite easy and rewarding. Then you can name offspring after your Uncle Joe, Aunt Agnes, Baby Matilda, or even yourself.
There are three common ways to create your own heirloom variety, and each can be done by the home gardener. The first method involves crossing two heirloom varieties, then selecting and genetically purifying their offspring into an open-pollinated form. Second you might be able to identify a plant in your garden that has already been crossed naturally, and then dehybridize it to an open-pollinated form. A third method is to dehybridize a commercial hybrid. While all of these methods starts differently, the way to “purify” tomato varieties is the same for all of them.
There are two basic ways to cross-pollinate tomato plants. The first method described is considered by many the “proper” way. The second approach is decidedly more casual and unpredictable, but also has it’s merits.
Select any two varieties as parents. Keep in mind that the more dissimilar the parents-in terms of fruit color, shape, and foliage-the more interesting the offspring will be. Choose one parent to be the recipient (female) of the pollen from the other parent.
Early in the day, select a newly opened blossom of the female parent. Using tweezers, carefully remove the pollen-bearing anthers, which will prevent the plant from self-fertilizing . (This step is trickier than it sounds, and should be practiced on a test blossom before doing it on a parent plant.) Then transfer the pollen from the anthers of the male parent to the stigma of the female parent. Do this by taking some pollen-bearing anthers in your hand and rubbing them against the female stigma. Another way to accomplish this is by using a clean cotton swab to gather the pollen and deposit it on the stigma. ( This method is considered “proper” because you actually prevent the blossom from self-pollinating by emasculation, or removal of the pollen-bearing anthers.)
Contrary to popular opinion, there’s no need to put an isolation bag over the new-fertilized baby tomato to protect the stigma from unwanted insect pollinators. There are many more pollen grains than ovules to fertilize, so possible visits by insect pollinators will usually not be successful. Some people, however, still like to protect the pollinated stigma with protective covering of Reemay or a similar porous but insect-proof fabric. Last, attach a tag to the stem of the fertilized blossom for easy identification.
A more casual approach to crossing involves not removing the anthers from the female parent plant. Transfer pollen from the male plant as described above, but allow the female parent to self-fertilize. If the anthers are not removed from the female parent, then pollen from two sources might be involved. This way, all of the F1 (First generation) plants grown out from this cross may not be identical, which would be the case if you remove the anthers from the recipient blossom. Since the ideal is to create new and interesting varieties, this method may give you more variety-but less control.
Selecting For A New Variety
Keep tabs on the fertilized blossom, and shortly you’ll see the ovary swell with a baby tomato. When the tomato is ripe, process the seeds by fermentation. Plant these F1 hybrid seeds the following growing season. All the plants and fruits that result should be identical-if only one kind of pollen did the fertilization. If two types were involved, you’ll usually see more than one kind of plant in this F1 generation. In this second season, you won’t be selecting plants because they should be identical if one kind of pollen was used for crossing. The “casually” pollinated plant may give you F1 seeds that result in more than one plant or fruit type. If so, make your selection(s) at this point. This season, all you want to do is harvest ripe fruit and save the seed, now called F2 seed.
In your third year, plant out as many of the F2 seeds as possible because you will see a big cross-section of plants and fruits. A wide range of different plants should emerge from this crop because the genes from the parents are sorting themselves out. It is from this crop that you will be selecting the plants to purify genetically.
Select a plant with fruit, foliage, and taste that appeals to you and save only that seed (now considered F3 seed) for next year. Plant the seed again, saving only seed from the plants that match the previous generation. You’ll notice that other strains or plant types continue to appear, but select only for the strain or plant type you chose last year. Repeat this process year after year, until the strain you’ve selected grows from every seed that you’ve planted. At this point, the strain is considered open-pollinated and qualifies as a new variety. The process may take three to ten years, depending on the particular genetic traits involved.
Once you’ve created the variety, it’s yours to name, brag about, and share with others. You can grow this new variety every year from saved seed as long as a chance cross-pollination or spontaneous mutation doesn’t occur.
Dehybridizing a Naturally Created Heirloom Hybrid
When you plant saved seed from a specific variety, a completely unexpected variety will sometimes result. Instead of the expected potato leaf foliage with huge pink fruits, for example , you get plants with red globe-shaped and regular foliage. If this happens, you can usually conclude that the variety was cross-pollinated naturally by insect pollinators in the previous year. Instead of getting upset, seize this opportunity to create your own heirloom.
The seed saved from the previous year that gave rise to the cross-pollinated plants was the F1 hybrid seed. Seed from the cross-pollinated plants is F2 seed-the initial cross-pollination has already been done for you. Simply plant the F2 seed and select the plant you want to purify, and continue growing it out until it stabilizes, as described above.
Dehybridizing a Known Commercial Hybrid
If you grow a hybrid tomato that you really like, you can dehybridize it and select it for it’s offspring. The seeds you save from the hybrid tomato are the F2 seeds. When you plant them, you’ll see a variety of plant and fruit types. Ultimately though, the choices for selection will depend on the parents used to make the original commercial hybrid seed. After planting the F2 seed, select the plants you want to dehybridize and follow the steps explained above until you have an OP form.
Genetic Traits for Selection
In addition to selecting tomatoes grown from F2 seed in terms of taste, fruit color, shape, and foliage, there are other characteristics you may want to consider when choosing among tomato offspring. Some growers want only the biggest tomatoes, and will save seed only from the biggest fruits generation after generation. You may want an earlier fruiting form of a known variety. One friend crossed Pink Brandywine with a number of early OP varieties in an effort to get an earlier fruiting variety with superior taste of Pink Brandywine. This is an admirable effort because most experienced tomato growers agree that the majority of early fruiting varieties are short on taste. The point is to use your imagination when deciding what characteristics to select for in your own crosses.
How Many Plants Do I Have To Grow Out?
The whole business of cross-pollinating and hybridizing tomatoes can get very complicated if you wish to be more scientific than I have been in this chapter. In the book Breed Your own Vegetable Varieties by Carol Deppe, there is a chart that indicates how many plants you should grow in order to see most of the possible genetic combinations of plants and fruits from your crosses. However, it can be just as rewarding-and a bit less rigorous-to grow out as many plants as your space allows, and follow the genetic traits that result. A little luck also helps. One amateur hybridizer sent me F2 seed to grow out. He knew what genes were involved, and had calculated that one of sixty-four plants would have the desired characteristics. I grew out only eight plants the first year and found the desired plant and fruit. Yes, I got lucky, but you might, too.
Tomato Traits And Genetics
You might recall from high-school biology that certain genetic traits are referred to as being either dominant or recessive. The genes of heirloom tomatoes are no different in this regard. The most scientific-minded tomato hybridizers factor in the basic traits when crossing tomatoes. By doing the same thing, you can make more educated choices when selection parents for new varieties.
Red pigment-the color that represents “tomato” for many-is dominant over yellow, for instance. If you cross yellow fruit and red fruit,, the F1 generation will bear red fruit. You won’t see various combinations until the F2 generation. Potato-leaf foliage is a recessive trait, but it’s possible to cross two varieties with regular-leaf foliage and get an offspring with potato-leaf foliage. In this case, there would have to be recessive potato-leaf genes in both parents of the cross.
Spontaneous mutations occur all the time. One gene that frequently mutates is the one responsible for skin color. If the skin yellow and the interior of the tomato is red, the tomato will appear red. If the skin color mutates to clear colored , then the tomato appears pink, but the interior is still red. In fact, there is no difference between pink and red tomatoes other than their skin color.
At the end of the day, you don’t need to love genetics to enjoy creating your own heirloom tomatoes. It’s great fun, and you may end up with a tomato you can call your own.
This is a chapter from the book: 100 Heirloom Tomatoes for the American Garden by Carolyn J. Male
If you have a love for tomatoes as I do, this is a must have book.