Building Digital Education of Heirloom Crops
for the Resilience of African Food Systems in the Climate Crisis
Lecture 4
Understand The Pollination!
Understand the pollination!
Seed saving is a fascinating process that begins with understanding plant biology. Pollination is a crucial process in the plant reproductive cycle. Plants produce fruits and seeds as a result of the pollination process.
Let's start with biology! [1]
The flower's male parts are the stamens with the anthers at the end. These are where the pollen (plant sperm) is produced and spread.
The female parts are at the bottom - the ovary, then the style, and at the top, the stigma where the pollen must land. From here, the pollen grows through the style and into the ovary to fulfill the fertilization.
In some plants, all flowers have both male and female organs. They are called perfect flowers.
Other plants have separate male and female organs in different flowers, though still on the same plant (e.g., pumpkin, melon, cucumber, maize (US corn). They are called monoecious.
In a few plants, the male and female flowers are found on different plants, so the whole plant is either male or female (e.g., asparagus, kiwi, spinach). These plants are called dioecious.
Pollination methods [1;2]
Self-pollinating
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Self-pollinating plants can use their pollen to fertilize their flowers. In some, the pollination even happens before the flower is open (peas, beans, lettuce, and most tomatoes). The pollen grains fall from the anther to the stigma, and when the flower opens, the whole thing is over and done. So, visiting insects cannot interfere with fertilization. In principle, you can grow viable seeds from just one plant of this type, but it is always better for genetic diversity to take seeds from several plants.
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Most self-pollinators can use pollen from other plants of the same species. This happens very rarely in some cases (mentioned above), but the risk is much bigger in other cases.
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Some self-pollinators are also popular with insects and are therefore at risk of being contaminated with pollen from other plants (e.g., chili, pepper, broad (fava) bean, eggplant).
Cross-pollination
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These plants are also called out-crossers. They primarily use pollen from other plants and hence need someone or something to bring the pollen from one plant to another – most commonly insects or wind.
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Insect pollinated: E.g., cabbages, carrots, pumpkins, squash, leeks, onions.
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Wind pollinated: E.g., maize, spinach, beetroot.
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A particular group of out-crossers is self-infertile. This means that one plant cannot use its pollen to fertilize other flowers on the same plant. It must have pollen from another individual. Self-infertility is a good protection against spontaneous inbreeding. E.g., Cabbages, carrots, maize, rye.
Artificial pollination
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Hand pollination: The manual transfer of pollen from the anther of one flower to the stigma of another, allowing for precise control over the pollination process.
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Pollen mixtures: A method involving the mixing of pollen from various plants and its subsequent application to stigmas. While faster than hand pollination, this approach offers less precision.
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Purpose:
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To manipulate the pollination process.
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To produce seeds with specific desired characteristics.
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Hybridization
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Hybridization is the process of crossing two different varieties or species to create a hybrid offspring.
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Hybridization is often used to improve crop yield and disease resistance.
What is the significance of the pollination method in seed preservation? [1]
The pollination method is crucial for seed saving.
Self-pollination, where a plant fertilizes itself, allows for easy seed collection from a single plant but can limit genetic diversity. For instance, you can propagate plants from a single bean and obtain high-quality seeds.
Cross-pollination, where different plants of the same species fertilize each other, promotes genetic diversity and can make plants more resilient to diseases and pests. However, cross-pollination requires multiple plants to flower simultaneously and exchange pollen to produce high-quality seeds.
How can we tell how a plant is pollinated?
Examine the plant's flower:
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If the stigma is not visible, the plant is likely self-pollinating.
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If a plant has showy and fragrant flowers, it is most likely pollinated by insects.
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If the flowers are small and inconspicuous and release pollen during flowering, the plant is likely wind-pollinated.
How to prevent unwanted cross-pollination [2;3]
To prevent unwanted cross-pollination, which can impact seed quality and the characteristics of subsequent generations, it's essential to isolate varieties from unwanted pollen. There are several effective methods:
Physical isolation:
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Distance: Plant different varieties as far apart as possible. This makes it more difficult for pollinators to travel between them, reducing the risk of cross-pollination.
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Barriers: Use physical barriers such as tall fences, walls, or windbreaks to prevent pollinators from moving between different varieties.
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Grow only one type of plant: Ensure that no other plants nearby can pollinate your desired crop. For example, grow only one kind of squash, cucumber, melon, or watermelon.
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Grow many plants: When growing insect-pollinated plants, plant a large number and collect seeds from the center of the field. This is because insects fly from plant to plant, carrying pollen on their bodies.
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Cover with insect netting: When using insect netting, provide a suitable environment for the specific pollinators you want to attract. For example, food sources for the pollinators should be placed inside the netting.
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Isolation bags: Cover individual flowers with paper or cloth bags to prevent accidental pollination.
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Isolation rooms: Grow plants in special rooms where pollination conditions are controlled.
Temporal isolation:
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Different flowering times: Choose varieties that have different flowering times. This ensures that when one variety has finished flowering, the other has not yet begun, minimizing the risk of cross-pollination.
Genetic isolation:
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Self-pollinating varieties: Choose self-pollinating varieties that do not require cross-pollination. These are suitable for seed production even in small areas.
Artificial pollination:
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Hand pollination: If you want complete control over the pollination process, you can do it yourself by transferring pollen from one flower to another using a brush or tweezers. Then, isolate the pollinated flower to prevent it from receiving pollen from other plants.
Why are these methods important?
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Creating new varieties: Artificial pollination allows for the combination of desirable traits from different plants, leading to the development of new varieties.
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Preserving genetic diversity: Isolation and selective pollination help preserve rare and endangered plant varieties.
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Improving fruit and seed quality: Selected plants are often more resistant to diseases, pests, and adverse environmental conditions.
References:
[1] - Growing Seed Savers. (2019). A Guide To Seed Saving [Brochure].
https://growingseedsavers.org/content/pdfs/GSS_Guide_to_Seed_Saving_ENG_Spreads.pdf
[2] - Frosamlerne (2019). Presentation "Basics about seed saving", project "Growing Seed Savers", https://growingseedsavers.org/educational-program-for-seed-saver/ .
[3] - Diyseeds (2022), https://www.diyseeds.org/en/films/ [Movies]
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.' The project was funded by the Ministry of Foreign Affairs in 2024 from the development cooperation budget. This content reflects only the views of the project partners.
