If you have a plant that’s a result of a cross between at least two other plants and you want to create a new stable variety from this plant, you must go through a process called dehybridization.
You can dehybridize a simple F1 hybrid variety (two plants crossed), but you can do the same thing with a grex (more than two plants crossed) as well.
I’ve mentioned in recent posts how important is is to start with the right kind of seeds when seed saving and breeding plants. Some people may be wondering why you couldn’t dehybridize a commercial F1 hybrid variety the same way you could an F1 hybrid created in your garden.
The issue is usually if you want the genes contained in a commercial variety in your garden. For example many commercial tomato varieties are bred to have tough skins or be suitable for transporting long distances. Many varieties of other plants are genetically programmed to produce their harvest all at the same time (often called ‘all at once’ types), which is handy if you are a farmer harvesting with a tractor but most gardeners would rather have a sustained harvest over a longer period. There are many other traits that exist in commercial hybrid varieties that aren’t necessarily desirable in a home garden.
If however you come across a commercial plant variety that you really want to keep and dehybridize, it’s often possible. For example, there have been a number of efforts recently to dehybridize the very popular commercial Sun Gold variety tomato. There have been a number of similar efforts made with commercial varieties in the past, and some of these efforts have been more successful than others.
The Process
As I’ve mentioned before, when two different stable varieties of plants are crossed, an F1 hybrid is created. If seeds from this generation are saved and replanted, the result is an F2 hybrid followed by an F3 and so on.
The F1 generation is distinct. That is if you grow more than one plant from this generation, they will all be the same. If you create more seeds by making a new cross from the same parent plant varieties, these seeds will also produce more of the same identical plants.
When starting with hybrid, the F2 generation the plants will start to show genetic instability, and the plants will all be different. In fact, the F2 generation will be the most unstable. It’s a good idea to grow a large number of plants in the F2 generation and save seeds only from those that have the most desirable traits, in order to take advantage of the large number of differences.
At this point it’s a matter of growing the next generation from previously saved seeds and continuing to select the most desirable plants. If you come across a generation without plants with desirable traits, it can sometimes be necessary to replant the previous generation, so it’s a good idea to save seeds from earlier plantings. If you are dehybridizing an inbreeding plant and end up with more than one plant with different desirable traits, it may be necessary to cross pollinate these plants so the desirable traits are combined. If you are working with outbreeding plants they will probably be cross-pollinating on their own anyway, making good rouging practices very important.
If you decide along the way new genetic material is needed, you can also introduce the genetics of other plants by cross-pollinating with them. Consider that the more complex and varied you make the genetics, the longer it will take to dehybridize and stabilize the variety.
After a number of generations of saving seeds from desirable plants, and rouging undesirable plants, the genetics of the new variety will begin to stabilize and you will seed fewer differences between the plants. Eventually, you will have a new stable open pollinated variety. Different plants take longer or shorter times to stabilize, ranging from a couple of years to as many as 10-15.
Sounds like an interesting experiment. I am often interested in certain types of disease resistance in tomatoes. Though previously I’ve been interested in trying to cross a naturally disease resistant strain with a heritage tomato whose flavour I like.
If I ever get enough space, I think I’ll try this with some of the brassicas. There are very few heritage strains of complex brassicas left like broccoli, and cabbage. At least according to the databases I’ve checked.
Thanks again!
I am often called upon to explain what a hybrid tomato is,and that’s not difficult. But your article on dehybridizing is very interesting to me. I also know that a lot of people do want to dehybridize Sungold. I had a tomato volunteer spring up this year amidst my pepper bed, and before I could pull it out, it had set some fruit that looked and tasted exactly like Sungold. Now I know that the previous year that’s where my Sungold plant was, and this volunteer is clearly from that plant. The fruit tastes just as good as Sungold, so I went ahead and saved the seed to see what it could produce next year. Do you think it would be worth a try?
I see in the Seed Savers Exchange Yearbook (the book members use to exchange seeds between themselves) that a couple of different people are offering versions of dehybridized Sungold. One person mentions theirs is not as good as the hybrid version. Just the fact that SSE members are offering seeds suggests that some people are having luck with it.
I would say if you have seeds from a F2 volunteer plant that tastes just as good as the original, then your chances of eventually getting a stable are pretty good. It’s worth a try!
If you are interested in trying some other peoples attempts, consider joining the SSE or making friends with someone near you who is already a member who can order the seeds for you.