Pollination is a key procedure in both humans managed and natural-terrestrial ecosystems. It is vital to food production and human livelihood and connects wild ecosystems directly to the agriculture production system. It is a crucial facility that is heavily dependent on the symbiosis among pollinators and pollinating species. There are several types, with significant importance, which vary among flowers according to crop and flower physiology.
Pollination is the process by which pollen is transferred from the anthers (male reproductive structures) to the stigma (female reproductive structure) of a flower. This transfer of pollen is necessary for fertilization to occur, which is the first step in sexual reproduction in flowering plants. During fertilization, the male gametes (contained in the pollen) fuse with the female gametes (contained in the ovules) to form a zygote, which will eventually develop into a new plant.
Pollination can be carried out by a variety of agents, including wind, insects, birds, and other animals. The anthers produce and release pollen, which is then carried to other flowers by these agents.
Transfer of pollens (male gametes) from the anthers of male flowers to the stigmas of female flowers (same or an-other).
Etymology
The word “pollination” comes from the Latin word “pollinare,” which means “to sprinkle with pollen.” This word is derived from “polline,” the Latin word for “pollen.” Pollen is a fine, powdery substance produced by the male reproductive organs of flowering plants. It is composed of tiny grains that contain the male gametes, or reproductive cells, needed for fertilization.
Pollinators
Pollinators are animals that transfer pollen from the male reproductive organs of flowers to the female reproductive organs, enabling fertilization and the production of seeds. Pollinators are an essential part of the reproductive cycle of many flowering plants and play a crucial role in the production of many crops.
There are many different types of pollinators, including insects, birds, bats, and even small mammals. Some of the most well-known pollinators include bees, butterflies, moths, hummingbirds, and bats. These animals are attracted to flowers for their nectar and pollen, and in the process of feeding, they pick up and transfer pollen from flower to flower.
Pollinators are important not only for the production of crops, but also for the health of ecosystems. Many plants rely on specific pollinators for their reproduction, and the loss of these pollinators can have cascading effects on the entire ecosystem. For example, the decline of bees and other pollinators has been linked to declines in the populations of many plants, including some that are important food sources for other animals. In recent years, there has been increasing concern about the decline of pollinators, and efforts have been made to understand and protect these important species.
Global statistics of pollination
According to the Food and Agriculture Organization of the United Nations (FAO), approximately 75% of the world’s food crops are dependent on pollinators for their production. This includes a wide variety of fruits, vegetables, nuts, and seeds that are important sources of nutrients and energy for people around the world.
Insects, particularly bees, are the most important pollinators for many crops. There are approximately 20,000 known species of bees, and they are responsible for pollinating a wide variety of crops, including almonds, apples, avocados, blueberries, cherries, and many others.
However, pollinator populations, including bees, have been declining in many parts of the world due to a variety of factors, including habitat loss, pesticide use, and climate change. This has led to concerns about the potential impacts on global food production and the overall health of the ecosystem.
According to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), approximately 16% of all known insect species, including pollinators, are threatened with extinction. This includes approximately 40% of all known species of bees, which are the most important pollinators for many crops.
The decline in pollinator populations has been linked to a range of negative impacts, including reduced crop yields and reduced nutritional diversity in the foods that are available to people. It has also been linked to negative impacts on the overall health of the ecosystem, as pollinators play a vital role in the pollination of wild plants and the maintenance of biodiversity.
Types of Pollination
These types affect the productivity and the fertilizing ability of crops. Plants have two types of pollination:
- Self-pollination
- Cross-pollination
Self Pollination
This is the simplest type; it involves only one flower on the same plant. In this method pollens from anthers of the same flower directly fell onto the stigma.
Self-pollinating plants are less dependent on external factors that trigger pollination. Wind and other small insects act as pollination initiators that regularly visit the flowers. The similar length of anthers and stigma act as a facilitating factor in pollen transfer in self-pollinating flowers.
Self-pollination is generally less advantageous for plants than cross-pollination, as it can lead to a decrease in genetic diversity and an increase in the frequency of negative genetic traits. However, self-pollination can be advantageous in certain circumstances, such as when a plant is growing in a isolated location where cross-pollination is unlikely to occur.
Types of Self-Pollination Based on Flower
There are two types of pollination based on flowers:
1. Autogamy
“Transfer of pollen (male gametes) from the anther to the stigma (female) of the same flower. E.g., Sunflowers, peas, orchids, etc.”
Autogamy is a form of self-pollination in which a flower pollinates itself. This can occur when the anthers and stigma of a flower are able to come into contact with each other, either through the movement of the flower itself or through the actions of insects or other agents. Autogamy can also occur when a flower is able to self-fertilize, even if the anthers and stigma are not in close proximity to each other.
Autogamy is a common form of self-pollination in many plant species, particularly those that have adapted to grow in isolated or inhospitable environments where cross-pollination may be unlikely. It can be an important mechanism for the reproduction and survival of these plants.
However, autogamy can also lead to a decrease in genetic diversity, as it does not involve the exchange of genetic material between different individuals. This can result in an increased frequency of negative genetic traits and a decreased ability to adapt to changing environmental conditions. As a result, many plant species rely on cross-pollination in addition to or instead of autogamy for their reproduction.
2. Geitonogamy
“Transfer of pollen (male gametes) from anthers of one flower to the stigma of another on the same plant. E.g., Corn, etc.”
Geitonogamy is a form of self-pollination that occurs when pollen is transferred from the anthers of one flower to the stigma of a different flower on the same plant. This can occur when the flowers of a plant are closely spaced and the anthers and stigma of different flowers come into contact with each other, either through the movement of the flowers themselves or through the actions of insects or other agents.
Advantages and Disadvantages of Self Pollination
This type of pollination does not require the involvement of any outside agents, such as wind, insects, or animals. There are both advantages and disadvantages to self-pollination for plants. Some of the advantages of self-pollination include:
- Self-pollination can be a reliable and efficient means of reproduction for plants, as it does not depend on the availability or behavior of external pollinators.
- Self-pollination can be an important mechanism for the reproduction and survival of plants in isolated or inhospitable environments where cross-pollination may be unlikely.
- Self-pollination can be a quick and easy way for plants to reproduce, as it does not require the production of nectar or other rewards to attract pollinators.
However, there are also some disadvantages to self-pollination:
- Self-pollination can lead to a decrease in genetic diversity, as it does not involve the exchange of genetic material between different individuals.
- Self-pollination can result in an increased frequency of negative genetic traits and a decreased ability to adapt to changing environmental conditions.
- Self-pollination can be less advantageous for plants than cross-pollination in terms of the production of larger or more vigorous offspring.
Cross-Pollination
A more complicated type of pollination is in which pollens are transferred from the anthers (male) of one flower to the stigma (female) of another flower. Increased genetic diversity is experienced in this type, as different flowers share and mix their genetic material to produce unique progenies. Several physiological and environmental factors affect its efficiency.
Many plants are dependent on cross-pollination for their reproduction, as it allows for the exchange of genetic material between different individuals and can lead to the production of genetically diverse offspring. This can be advantageous for plants, as it can increase the adaptability and survival of the species in changing environmental conditions.
Cross-pollination can be carried out by a variety of agents, including wind, insects, birds, and other animals. Each type of pollinator has its own unique characteristics and behaviors that can influence the effectiveness of cross-pollination. For example, some pollinators are more selective in the flowers they visit, while others are more indiscriminate. Some pollinators are more efficient at carrying pollen from one flower to another, while others are less effective.
Methods of Cross-Pollination & Flower Types
There are 3 methods of cross-polliination depending on the pollinating agents:
1. Wind Pollination (Anemophily) – Wind acts as an agent to transfer pollen from male to female. Some plants, such as grasses and conifers, are pollinated by wind. These plants produce large amounts of lightweight pollen that is easily carried by the wind.
Anemophilous Flowers: Anemophilous flowers are flowers that are adapted to be pollinated by wind. Pollen of these flowers is non-sticky, very light, and sometimes winged. E.g., Oats, Wheat, Rice, Maize, etc.
2. Water Pollination (Hydrophily) – Water act as an agent to transfer pollen from male to female. Water pollination is most common in aquatic plants, such as certain species of water lilies and pondweeds. These plants are adapted to grow in aquatic environments and have flowers that are adapted to release their pollen into the water. Some terrestrial plants, such as mangroves, also have adaptations for water pollination, as they grow in areas where their flowers may come into contact with water.
Hydrophilous Flowers: Water-pollinated flowers are commonly very small and undistinguishable from other active ingredients. They have no odor nor coloring on petals and their pollens can efficiently swim in the water. E.g., Hydrilla, Vallisnaria, Zostera, etc. Moreover, humidity also attracts the bees which helps them boost pollination.
3. Animal Pollination (Zoophily) – Animals act as an agent to transfer pollen from male to female. Bats are important pollinators for many plants, particularly in tropical and desert regions. These flying mammals are attracted to flowers for their nectar and pollen, and in the process of feeding, they transfer pollen from flower to flower.
Zoophilous Flowers: Animal-pollinated flowers, pollens of these flowers have a stick body that helps them to stick on the animal body and transfer from one flower to another. E.g., sunflowers, roses, tomatoes, etc.
3.1. Bird Pollination (Ornithophily) – Birds act as an agent to transfer pollen from male to female. Some plants, such as certain types of orchids and bromeliads, are pollinated by birds. These plants typically have bright, showy flowers that are adapted to attract birds, which transfer the pollen as they feed on the nectar.
Ornithophilous Flowers: Birds pollinated flowers, that are large in size and have a beautiful appearance, produce nectar, generally scentless and some flowers have an edible part that attracts the birds toward them. E.g., Bottlebrush, Bombax, etc. The common-visiting bird’s Hummingbirds, Crows, Honeybirds, Bulbuls, etc.
3.2. Insect Pollination (Entomophily) – Insects act as an agent to transfer pollen from male to female. Many insects, such as bees, butterflies, moths, and beetles, are attracted to flowers for their nectar and pollen. In the process of feeding, these insects pick up and transfer pollen from flower to flower, enabling cross-pollination.
Entomophilic Flowers: Insect-pollinated flowers, are attractive, have bright petals, and have a sweet fragrance to attract the insect. They normally have a wide stigma or anther on which the insect can land. Many flowers also produce nectar, -which appeals to butterflies, bees, or other insects. The spiny and sticky nature of pollen grains helps them to stick to the insect’s body and transfer to stigmas. E.g., Jasmine, Bougainvillea, Lotus, Sunflower, Cestrum, etc. The common-visiting insects are Bees, Butterflies, Wasps, Moths, and Drones, etc.
Advantages and Disadvantages of Cross-Pollination
This type of pollination requires the involvement of outside agents, such as wind, insects, or animals, to carry the pollen from one plant to another. There are both advantages and disadvantages to cross-pollination for plants. Some of the advantages of cross-pollination include:
- Cross-pollination allows for the exchange of genetic material between different individuals, leading to the production of genetically diverse offspring. This can be advantageous for the adaptability and survival of the species in changing environmental conditions.
- Cross-pollination can lead to the production of larger or more vigorous offspring, as it allows for the combination of beneficial traits from different individuals.
- Cross-pollination can be more efficient than self-pollination in some cases, as it does not rely on the movement or self-fertility of the flower.
However, there are also some disadvantages to cross-pollination:
- Cross-pollination relies on the availability and behavior of external pollinators, which can be unpredictable. This can make cross-pollination less reliable than self-pollination in some cases.
- Cross-pollination may require the production of nectar or other rewards to attract pollinators, which can be energetically costly for the plant.
- Cross-pollination can be less efficient than self-pollination in some cases, as it requires the involvement of external agents.
Steps of pollination
Pollination is a complex process that involves several steps. The 7 steps of pollination are as follows:
1. Pollen production: The first step in the process of pollination is the production of pollen by the anthers of the plant. Pollen contains the male gametes (sperm cells) that are necessary for fertilization.
2. Pollen release: Once the pollen is produced, it is released from the anthers of the plant. This can be done through a variety of mechanisms, including wind, water, or the action of pollinators such as bees, butterflies, and birds.
3. Pollen transport: The released pollen is then transported to the stigma of the same or a different plant. This can be done through the action of pollinators, or through the movement of wind or water.
4. Pollen germination: Once the pollen reaches the stigma, it germinates, or begins to grow, forming a pollen tube that grows down towards the ovules (female gametes) of the plant.
5. Pollen tube growth: The pollen tube grows through the style of the plant, which is the structure that connects the stigma to the ovules.
6. Fertilization: Once the pollen tube reaches the ovules, fertilization occurs, resulting in the formation of seeds.
7. Seed production: The fertilized ovules develop into seeds, which are contained within the fruit of the plant. The seeds can then be dispersed and carried to new locations, allowing the plant to reproduce and spread.
Importance of pollination
Pollination is an important process that is essential for the reproduction and survival of many plant species. There are several advantages to pollination for plants:
- Pollination allows for the production of seeds and fruit, which are important for the reproduction and survival of the plant.
- Pollination allows for the exchange of genetic material between different individuals, leading to the production of genetically diverse offspring. This can be advantageous for the adaptability and survival of the species in changing environmental conditions.
- Pollination can lead to the production of larger or more vigorous offspring, as it allows for the combination of beneficial traits from different individuals.
- Pollination can be more efficient than self-pollination in some cases, as it does not rely on the movement or self-fertility of the flower.
- Pollination can lead to the production of more flowers or fruit per plant, as it allows for the transfer of pollen from one plant to another. This can be advantageous for plants that rely on flowers or fruit for reproduction, as it can increase the number of seeds or fruit produced.
- Pollination can improve the quality and size of the fruit or seeds produced, as it allows for the combination of beneficial traits from different individuals. This can be advantageous for plants that rely on fruit or seeds as a food source for animals or humans, as it can increase the attractiveness and nutritional value of the fruit or seeds.
- Pollination can play an important role in improving the stability of crop production and decreasing year-to-year variability.
Challenges to pollination and pollinators
There are many challenges to pollination and pollinators that can have negative impacts on the health and survival of these important species. Efforts are being made at the local, national, and international levels to address these challenges and support pollinator populations. Several challenges to pollination and pollinators are:
Habitat loss and degradation: Pollinators, including bees, butterflies, and other insects, rely on a variety of habitats, including forests, grasslands, and wetlands, for food, shelter, and nesting sites. The loss and degradation of these habitats can have negative impacts on pollinator populations, as it reduces the availability of resources and suitable habitats.
Pesticide use: Pesticides, including insecticides and herbicides, can be harmful to pollinators, as they can kill or damage the insects and plants that they rely on for food and shelter. The use of pesticides can also disrupt the ability of pollinators to navigate and locate flowers, which can reduce their effectiveness as pollinators.
Climate change: Climate change, including rising temperatures and extreme weather events, can have negative impacts on pollinators, as it can alter the availability and quality of flowers and other resources that they rely on for survival.
Disease and parasites: Pollinators, including bees, can be affected by diseases and parasites, such as the Varroa mite and the American foulbrood bacterium, which can reduce their populations and impact their ability to pollinate.
Invasive species: Invasive species, such as non-native plants and animals, can have negative impacts on pollinators, as they can alter the availability and quality of flowers and other resources that pollinators rely on. They can also compete with native species for resources and habitat.
Monoculture: The cultivation of a single crop over a large area can have negative impacts on pollinators, as it reduces the availability and diversity of flowers and other resources that they rely on for food and shelter.
Urbanization: Urbanization, or the expansion of cities and towns, can have negative impacts on pollinators, as it reduces the availability of natural habitats and can increase the use of pesticides and other chemicals that can be harmful to pollinators.
Pollution: Pollution, including air and water pollution, can have negative impacts on pollinators, as it can alter the availability and quality of flowers and other resources that they rely on for survival. Pollution can also be harmful to pollinators directly, as it can damage their bodies and impair their ability to function.
Examples of Diversity
- Shape and size of an apple
- The oil content of rape-seed
- Shape and shelf-life of strawberries
Examples of Self and Cross-Pollinating Crops
| Self Pollinated Crops | Cross Pollinated Crops |
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