The turnips for seed are now in bloom. It is the swedish heirloom Ljungdalen. One selected turnip didn’t survive the winter, but 15 are blooming. Swedish seedsavers SESAM recommend minimum 5 plants and preferably 20 or more. Ideally I should have a few more plants in bloom, but its allright. If I make a bacth more, before the original seeds get too old, I can quickly have more than 20 plants in all in my genepool. Then I just have to remember mixing the two seed batches, and variety in the genepool is secured.
This variety have two distinct colors of the roots. As I weighted the number of each color according to what I had seen in my garden, to conserve the balance of the two colors, I at the same time ensured a certain plurality in the genes. I believe 15 will be a sufficient number in this case. But I would never go below the minimum of five plants, even if I had more distinct features to balance with.
Did I only have room for 5 plants, I would grow seeds every year, and then in a jar put 50 seeds every year. Over 10 years 500 seeds would have passed the jar and mixed up on the way. A jar of a well mixed genepool. For the first years I would grow out from the original batch, not starting to take seeds from the jar, until more than 20 plant are parenting the jar. Turnip seeds can be expected to last for 10 years.
Why a minimum of five plants?
Most Brassicas, including turnip, are self incompatible. They have a genetic barrier to ensure outbreeding. A single plant can’t pollinate itself or any other plant with the same version of the genetic barrier. Having let’s say two plants in bloom, there’s a high risk the both have the same version, and there will be produced no seeds on either plant. With three plants the risk is much smaller, but still significant. Only with five plants or more is the risk so small that we can ignore it.
In outbreeders we also want the genes to mix well in every generation. It allows a good adaptability in years to come, f.ex. different genes for disease resistance will all be secured for future generations if “the cards are shuffled”.
There’s a lot of tips and tricks to overcome seedsaving in small private gardens 🙂