the question of how many plants to save

[DellaHedger]

Hi, we have recently started a new seed circle where I live We are in the early stages of setting up and there is a discrepancy between some members which I'd like some advice on please. What's a good number of plants, such as brassica to seed save from?
As a realistic number we felt that asking people to save between 16-20 plants would be possible in terms of space and keeping the strength of the seed. One of our members feels strongly that to protect seed diversity/resilience we need to save between 20-50 plants which makes seed saving for some much more tricky
Please can you share your experiences of a realistic number of plants to save seed from that will last!
Thank you
Della

[Galina]

Hi DellaHedger and welcome. Good news on the new seed circle. There is a large difference between inbreeding plants and outbreeding plants. Inbreeders such as peas, French beans, tomatoes, lettuce do not need others and do not suffer from inbreeding depression, which is getting weaker because not enough plants were used for seed. So in principle you could save good seeds from just one bean plant, just one pea, lettuce etc. Just in case that one plant has a problem or happens to be not a good plant, I would go for two or three. Note that runnerbeans do cross, as do broad beans. Also peppers cross and need to be isolated to prevent bee access.

There are plants such as squashes, melons, cucumbers, ie the cucurbita, which are only very slightly inbreeding. Which means you can self them, ie take a male flower and a female from the same plant, but it is better to take a male from another plant. Of course they must be isolated and handpollinated, not just allowed to cross or the bees will create crosses where we want pure breeding varieties.

Then there are root vegetable. For carrots and parsnips which are outbreeders, you need to have at least a dozen ditto leeks, 20 are better and crossing must be prevented. So only one per garden if the neighbours don't grow them to flowers (luckily most neighbours don't have flowering leeks or parsnips, even if they do grow them. Brassica also need a dozen to 20, which is quite a commitment if you want to save a cabbage for pure seeds. Ditto beetroot and radish

The worst for inbreeding depression is corn. The advice is 100 plants. That is a big commitment.

For a beginning seed circle unless people are experienced or want to take it on, the outbreeders are more difficult.

How to save good seed really varies from vegetable to vegetable. RealSeeds has seedsaving instruction in their catalogue pages. I have several seedsaving books and can check the more unusual vegetables for you if you need advice. Good luck with the circle Della.

[Galina]

https://www.realseeds.co.uk/brassicaseedprocessing.html

This as a guide. If that member wants to do it themselves with 50 or more plants that's fine. Guess they have a field available and materials for huge isolation cages too. If they just want others to do it this way and be prescriptive about it, that will put off almost everybody. With the winter radish I maintain, I use 12 really good roots. Last year I saved seeds from red mustard and I had 16 plants. Haven't grown those yet but I expect the number will do fine. Turnips which I have saved and regrown several times are also at least a dozen. My turnips are interesting. The first year they needed fleecing, but by now they are fully winter hardy one of the best benefits of saving your own seeds is the adaptation to local conditions. Guess that has been adding cold tolerance to the gene pool.

[Galina]

There is also the concept of seed saving over time. Save from n plants one year and then save from n plants the next year and following years. Mix those and you have saved seeds from a much larger population. Easiest if the first year saved seeds are stored in the freezer. This is what I do with corn. Admittedly I have never shared my corn seeds, because I am still testing the validity of this method over time and it takes time. I only know this method from books.

[DellaHedger]

Thank you so much for all this..... I really appreciate the time you're taking to reply to me, it's much appreciated.

[triffid]

Hi DellaHedger, welcome.

Great to read that you've started a local seed circle. Good luck, it should be great fun!

The population size required to maintain genetic diversity varies greatly between species. For most flowering plants, one can roughly divide into two main groups: inbreeders (self-pollinators) and outbreeders (cross-pollinators). Brassicas are outbreeders (some more strongly than others) and you will need to select from at least 50-80 plants, which means realistically you would start off with more than this and select the best. Corn is another strong outbreeder and requires a population of 80 plants minimum.


Natural inbreeders such as peas, French beans, and lettuce only need as many plants in a population as one is willing to grow, but older varieties would still benefit from as large a population as possible to keep any genetic heterogeneity.

I hope you don’t mind me quoting from The Organic Seed Grower ( John Navazio, 2012) - it’s where I get most of my information on the topic! I’ll include the whole paragraph titled ‘Minimum number of plants needed’:

In order to maintain this genetic diversity, anyone producing seed will usually need to grow a minimum population of between 20 and 200 plants, depending on the crop and its mode of pollination, whenever they want to faithfully reproduce the crop and maintain the inherent genetic variation of a particular variety. Growing a self-pollinated crop may require at least 20 to 50 flowering plants that are all contributing to the population after selection is completed. This number recognises that many selfers are more genetically diverse than what is usually recognized by many plant breeders or seed companies that only work with genetically narrow pure lines in these crops.

Non-hybrid cross-pollinated crops are always harboring a wealth of genetic variation, especially if they are robust, healthy varieties that are suitable to organic agriculture. The minimum number of 200 plants comes from my own experience with crossers and some of the disasters I have witnessed when seed crop populations have dropped below this number.

Corn breeders and corn preservationists often cite this number as well when talking about retaining genetic breadth in a corn population. Always count on losing at least half of the population that you started out with due to attrition, especially when storing roots or selecting diligently against many of the obvious flaws that are revealed in older, poorly maintained populations or varieties of crossers. Remember that the final selection isn’t truly done until after the plant is well established in the flowering stage and reproductive maladies appear.
The best seed growers are definitely the ones who view their crops on a regular basis through all of the stages of their life cycle in anticipation of eliminating any poor plants. In some well maintained, highly selected cross-pollinated crop varieties it is possible to reproduce them successfully with a population of as few as 80 to 100 plants, but it is up to you as the seed grower to make sure that you are maintaining the valuable genetic variation of that variety when you are growing a seed crop of this type with less than 200 plants. It is also important to remember that all of the numbers given in this section refer to the number of fully fertile, healthy plants, for both selfers and crossers, that contribute to the final population.

Broad beans, runner beans, squash, courgettes, cucumbers and some tomatoes can and will cross within their respective populations thanks to busy pollinators, but are self-compatible and do successfully self-pollinate. So in theory they do not need a large population but you must be vigilant against cross-pollination between varieties if you want to keep the seed true-to-type in the next generation.

[triffid]

It is likely that brassica seed in circles has been saved from a relatively low number of plants, and of course it is possible, but the genetic integrity of that line will be weakened, severely so if it is an ongoing practice.
Adequate population size may not be too space expensive depending on the type of brassica being grown. For example, it's a lot more feasible for the home/allotment gardener to find space for 80 breakfast radishes rather than the same number of cabbages or cauliflowers.

If your circle is set on growing big brassicas, would it be possible for each participant to grow 20, select from 10-15 after roguing and selection, and mix up the seeds from each crop?

[DellaHedger]

Yes, I think that's where we're probably heading... asking too households to grow each kind of brassica we want.

[Jang]

It’s also important for those households to be sure there are no wild brassicas, of which there are quite a lot, nearby. Or of course neighbours growing brassicas.

[jayb]

Hi DellaHedger, another Welcome from me.

we have recently started a new seed circle

How exciting, I haven't been part of a Seed Circle for a few years but loved taking part and have many shared treasures. Do tell us more about your Seed Circle, I'm a little envious!

Several years back I grew Gilifeather turnips (Swede) for a SC, from memory it would have been around 20 plants or slightly over. Someone else by chance also grew Gillifeather and we were both able to send in seeds. I don't know how much this may or may not have helped with maintaining diversity. I grew several other Brassicas for seed, I'll see if I can locate any notes.

[DellaHedger]

Hi, well I guess it came about because I started to be aware of how sought after seed was becoming after covid and I thought about how all my seed was open pollinated so we may as well get a group together. There's currently about 15 households interested and we want to keep it to this sizer now so it doesn't get too out of hand and we figure out how we all work together as a group. I guess I'm trying to figure out ways to incorporate a small back yard gardener and people who have larger areas to grow food and ensure that there is a sense of equality and ease and fun for everyone! Any notes you can find on your brassicas would be much appreciated!