Building Digital Education of Heirloom Crops
for the Resilience of African Food Systems in the Climate Crisis
05 Lecture - Conservation of the properties of a variety
Intro: This lecture is part of a project to improve sustainable agriculture in Africa, funded by the Latvian Ministry of Foreign Affairs.
Main Content: To make sure that old varieties do not deteriorate, seed savers have to know how to avoid losing parts of a variety’s gene pool, which could lead to inbreeding and loss of vitality. At the same time, we also have to know how to avoid contaminating these varieties with pollen from another variety of the same species.
Call for action: Find a plant in your garden that you admire and would like to preserve its characteristics. Perhaps you have inherited this plant from your parents? Learn about this plant and its reproduction, try to understand what isolation methods would need to be applied in your garden to propagate it, preserving its good qualities. Is it practically feasible?
Selection of plants for propagation
Since late in the Stone Age, farmers and gardeners have worked to improve the quality of their crops. Maybe they wanted bigger fruit, stronger plants, or earlier harvest. This process is called selection, or if it is done using modern methods, plant breeding.
Basically you never take seeds from sick or weakened plants. These specimens should be removed from the bed before flowering. In this way, they cannot participate in fertilization and spread their pollen to the strong and healthy plants.
In order to make a successful selection of which plants to take seeds from, you must consider the purpose of your seed saving.
Every seed saver may have different objectives, tailored to their specific needs and farming practices. Each goal is valid, but it is essential to identify it clearly and choose the appropriate strategy.
Let's list some potential goals for seed saving:
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Preserving the unique characteristics of heirloom varieties. This involves maintaining the traits of a specific, often older, variety of a plant.
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Developing a customized selection from a mixed population. This involves carefully selecting plants from a diverse group based on specific desired traits, to create a strain that is well-suited to your particular farming environment.
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Improving an existing variety. This involves selecting and propagating plants that exhibit specific desirable traits, with the aim of enhancing those traits in future generations.
How to preserve crop characteristics
When saving heirloom varieties, it's crucial to maintain their valuable traits (Conservation). This involves selecting offspring that closely resemble the parent plants.
Conservation
If the purpose of your seed saving is conservation of a certain variety, you have to take into consideration the whole gene pool of the variety. This means you will have to take seeds from a broad spectrum of plants, as long as they carry the characteristics of the variety.
To make sure that old varieties do not deteriorate, seed savers have to know how to avoid losing parts of a variety’s gene pool, which could lead to inbreeding and loss of vitality. At the same time, we also have to know how to avoid contaminating these varieties with pollen from another variety of the same species.
Avoid inbreeding
To avoid inbreeding it is important to know how many plants you need to grow for seeds. The more plants you grow, the better the chance that all the original genes are represented. This does not mean that you have to take seeds from each and every plant. If all the plants have participated in pollination, their genes will be represented in the seeds you get.
Some species like cucumber can make healthy seeds from a few plants over several years, but to make sure that the whole gene pool is intact, you had better have 10 plants.
Cabbage is at the other end of the scale. In a few years with too few plants, you will have lost the variety or degraded it substantially. They are self-infertile / self-incompatible.
A good trick to increase your available gene pool is to mix some seeds from this year’s harvest with some seeds from last year’s harvest and maybe even some from the year before that.
Therefore, never sow the last seed of a special variety unless it really is the very last seed.
Avoid contamination
To avoid contamination from other varieties, you have to know about your crop’s “sexual preferences” and how far apart from other pollen sources the plants will have to grow. See minimum distances in table “Guide to Seed Saving Recommended distances” (table 2 on page 19 https://growingseedsavers.org/content/pdfs/GSS_Guide_to_Seed_Saving_ENG_Spreads.pdf). However, if your garden is too small for safe distances, you can use some of the isolation tricks mentioned at the fourth lecture to ensure purity of your varieties.
RECOMMENDED DISTANCE AND CROP SIZE FOR SAFE SEED HARVEST
https://growingseedsavers.org/content/pdfs/GSS_Guide_to_Seed_Saving_ENG_Spreads.pdf page 19
The “Guide To Seed Saving” tables make recommendations on how to avoid both - detoriation and contamination - for two types of seed saving goals – hobby and conservation/sale.
Hobby
Hobby means that your seeds are for personal use only, or you share them with other amateurs. Furthermore, you are saving seeds of varieties which are easily replaced.
Conservation/sale
Conservation/sale means that your seed saving is about conserving the whole gene pool of a special variety, or your seeds are for small-scale marketing.
Distances
In the column for distances, you will sometimes find two numbers. This does not mean you have a free choice. It means that you have to consider the topography of your garden. Do you have buildings or tall hedges to shield different crops from each other? Do you have very few or many insects in your garden, and do you have a lot of flowers all over the place to distract the insects?
Self-pollinating varieties
These varieties are the easiest to handle. Here you need only a couple of meters between varieties and 5 – 10 plants of each variety.
Lettuce, peas and most tomatoes are safe self-pollinators.
Garden beans, fava beans, runner beans, capsicums, and scorzonera self-pollinate, but are also popular with insects and therefore prone to contamination with foreign pollen.
However, caution should be exercised, as sometimes a self-pollinated plant becomes accessible to pollinators and unwanted pollen can get into the flower.
Distance in time or space
As mentioned above, distance is one way to secure your plants from unwanted crossing. Grow only one variety each year and keep an eye on what your neighbor is growing. Most seeds stay alive for at least a couple of years, so you can grow two varieties in alternating years.
Covering
Self-pollinators can be kept pure by covering. Pull a bag (paper or thin cloth – absolutely not plastic) over the whole plant, or if it is too big to cover, over a branch with a few flower buds. The bag must be tied closely around the stem so that no insects can enter. Make sure you do this before the flowers open. To ensure a good pollination, you can shake the bag now and then, and when fruit is developing inside you can take away the bag and attach a marker to the branch to remind you where to harvest your pure seeds
Shielding
You can grow two varieties – one on either side of the house or a tall hedge - and so reduce the risk of unwanted pollination /contamination.
Cross-pollinating varieties.
Cross-pollinating varieties are more complicated to deal with. Distances have to be much greater. Foraging insects fly far and wide – bees can fly up to 3 km away from their hive. Moreover, plants that are dependent on visiting insects do whatever they can to attract them. They use scents and colour and they offer pollen and nectar.
Pumpkin and squash (Cucurbita species), cucumber (Cucumis sativus) and melon (Cucumis melo) are two different genera (plural of genus) and several different species, which do not cross with each other, but they cross energetically with other varieties of their own species. The Cucurbita family contains several species which do not cross with each other (e.g. C. maxima, C pepo, C. mixta and C. ficifolia). There are only small visible differences between them. Therefore, you have to know the Latin name to make sure which ones cross and which ones do not.
In this group, the male and female flowers are separate, but they are so big that hand-pollination is a possibility.
"Circle" - indicates the risks of unwanted cross-pollination between plants.
Pollination notes in the table:
SS: Almost exclusively self-pollinating.
S: Primarily self-pollinating, men will sometimes be pollinated by insects or wind.
S/O: Can self-pollinate, but will also frequently be pollinated by other plants of the same species.
O: Outcrosser, but can also self-pollinate for a few generations, before being weakened by inbreeding.
OO: Outcrosser, strongly self-infertile/self-incompatible. Few or no viable seeds from a single plant, suffers from inbreeding very quickly if too few plants are grown.
Example of the table 2
Hand-pollination
To be successful you have to keep an eye on your plants. The day before the flowers open, you cover them with a bag tied around the stem. You need at least one female flower and 4-5 male flowers – all bagged. The next morning when the flowers have opened, you pick the male flowers and strip them of the petals. Then you remove the bag from the female flower and smear the pollen from all the male flowers on the stigma. Finally, you cover the female flower again. When fruit is developing, you can remove the bag and put a marker on the fruit so you do not forget where the pure seeds are.
Cabbage (Brassica oleracea) is a troublesome species, which is insect-pollinated. Everybody crosses with everybody and you need at least 20 – preferably 40 – plants to avoid inbreeding. Therefore, if you want to grow seeds of a certain variety of kale, you have to keep an eye on all kales, cabbages, cauliflowers, Brussels sprouts, - - in the neighborhood. If they flower at the same time, they will cross. Danish Seed savers show their example of selection, overwintering and seed saving of Amager White Cabbage. https://www.youtube.com/watch?v=b4XEGL2pdvc
Carrots (Daucus carota) are also insect-pollinated, and even more troublesome. They cross not only with other carrot species but also with wild carrot. To avoid inbreeding you need at least 40 plants, and being biannual, they must survive a winter before producing any seeds. Carrots do not like frost so you have to protect them either with a thick layer of straw or by transplanting into a greenhouse for the winter. If you want to play with carrots, it can be recommended to have an experienced seed saver handy.
Shielding as mentioned above is not enough to protect a cross-pollinating variety, but it can reduce the necessary distance between two varieties.
Covering is a possibility with cross-pollinating varieties, but you need to cover the whole row and add some insects to secure pollination.
Vegetative Propagation
Many plants are commonly propagated vegetatively, a method that ensures "children" inherit the parent plant's traits exactly. This is because no cross-pollination or gene exchange occurs when creating a new plant in this manner.
Wikipedia defines vegetative reproduction as:
A form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or specialized reproductive structures, which are sometimes called vegetative propagules.
https://en.wikipedia.org/wiki/Vegetative_reproduction
Many plants naturally reproduce in this way, but it can also be induced artificially. Horticulturists have developed asexual propagation techniques that use vegetative propagules to replicate plants. Success rates and difficulty of propagation vary greatly. Monocotyledons typically lack a vascular cambium, making them more challenging to propagate.
Types of Vegetative Propagation:
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Tubers, corms, rhizomes (e.g., potatoes, dahlias)
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Division of clumps (many herbs)
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Cuttings, layering (many shrubs, berry bushes - currants are very easy to propagate)
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Bulbs, bulbils
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Grafting (fruit trees)
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Tissue culture (meristems - excellent for virus-free propagation and mass production of plants from a few cells, but requires a laboratory)
It's important to select healthy plants for vegetative propagation.
For heirloom plants, we strive to maintain their properties and prevent changes.
The content of this page was created as part of the project "Building Digital Education of Indigenous Inherited Crops for the Resilience of African Food Systems in the Climate Crisis Development". Project was funded by the Ministry of Foreign Affairs in 2024 from the development cooperation budget.
