Monday, December 8, 2008

Inbreeders and Outbreeders

Corresponding with readers is enjoyable. Sometimes we trade seeds, sometimes we just talk about gardening. One man I recently sent Cherokee Long Ear popcorn seed to sent me a thank you card and a donation. I sincerely appreciate that! I gave advice to a woman recently about which kind of Brussels sprouts to grow. A few days later I was reading Carol Deppe’s Breed your own Vegetable Varieties, and I realized I had left out some important information. I apologize!

She was looking for a compact variety to grow in her attached greenhouse. I suggested Jade hybrid because it is compact, and has been around a while. I hope it’s not too late to also recommend Long Island Improved, an open pollinated variety, which is also compact. But open-pollinated versus hybrid is not the problem. I told her she could save seeds and select for the compact traits in future generations, which is true, but probably not true for someone with a small amount of growing area, not for either variety. Most Brassicas are outbreeders.

This is a point that I was vaguely aware of, but I hadn’t a clear list in my mind of which classes of vegetables were outbreeders. I knew corn was one. I’ve been working with corn for some time. I knew spinach was another. I hadn’t tried breeding Brassicas before, at least not intentionally, so it wasn’t on my mind that they suffer inbreeding depression. Last year I let kale and collards flower at the same time, and saved seeds from each. I was hoping to find a cross, but since I’ve been reading up on it, I now realize that I should have had a larger population of collards than five plants. I might luck out with the kale, because there were several growing at once. In fact, I know there were at least some viable seeds, because there are volunteers growing. There are a few collard volunteers here and there as well, but it remains to be seen if any of them will be vigorous plants, because they might suffer from inbreeding depression. There might or might not be any crosses, but that’s beside the point.

Let’s say I am just growing one variety of Brussels sprouts. These plants don’t produce good seed, if any, from self-pollination. They need pollen from other Brussels sprouts plants nearby. In fact, if you intend to save seed and grow more of them next year, you’ll want probably close to a couple of dozen plants or more. It’s best to grow them in a sort of block rather than in a row for better pollination, just like corn or spinach. If I did save seeds from a population of two or three plants, then next year’s plants would all be close relatives, and the problem would compound the following year. Each generation grown in this manner would be more inbred, and the plants would suffer more and more until they were worthless.

Vegetables like beans, lettuce and tomatoes are natural inbreeders. They do not suffer inbreeding depression. You can save seeds from one plant and expect perfectly good plants to come form them.

Back to Carol Deppe’s book, I want to point out that while it sounds like something for plant breeders only, it is a great book to have on hand for any seed saver. I also want to stress the importance of reading Suzanne Ashworth’s Seed to Seed for any seed savers. It is a must-read. You can save yourself a lot of mistakes and head scratching by doing a little reading.


Ottawa Gardener said...

I figure with inbreeding depression the problem is limited genetics which leads to sickly plants that lack vigour. If you crossed collards and kale, assuming you got a cross that produced something you liked, it would have an increased amount of genetic diversity and therefore vigour? Still trying to figure these things out.

Bishops Homegrown said...

Yes, inbreeding depression is caused by a limited number of genetics and without knowing exactly how much pollen was crossed between the two species there is no way to know what to expect without growing the crosses, however, if the Kale and the collards did manage to cross, and I'm sure they were able to, you shouldn't be suffering from much of any inbreeding depression unless the cross of course was only made between a few flowers on one or only a few plants, in which case selecting for the traits you are after out of a small/tiny population will not be possible without inbreeding depression unless you plan to continuously make backcroses to the parent lines and then move forward. Brassicas can be a pain in the but when it comes to plant breeding and selection, but it is possible to ferret out what you are looking for.

Great Post Johno!