Pollination | What is Pollination? | Types of Pollination | Agents of Pollination | Self Pollination | Cross Pollination
Pollination | What is Pollination?
The transfer of pollen grains from anther of a flower to the stigma is called Pollination. Pollen grains cannot access the stigma by themselves. This requires an external agent. It can be air, water, animal, gravity or growth contact. Theophrastus wrote on pollination in Date Palm. Kolleuter (1761) recognized the importance of pollination in the establishment of insects and the role of insects.
Pollination is mainly of two types -
(i)Self-pollination
(ii) Cross-pollination
Self pollination
The transfer of pollen grains from anther to stigma in same flower or flower of same plant is called self pollination.
Accordingly, there are two types of self-pollination -
1. Autogamy
2. Geitonogamy
1. Autogamy
Autogamy is self-fertilization in organisms, which is a fusion of two gametes coming from the same organism.
It is especially observed in flowering plants. Therefore, autogamy can be considered as a type of self-pollination, where pollen grains from the anther of a flower accumulate on the stigma of the same flower.
Genetically identical offsprings are produced by autogamy.
Flowers using autogamy with multiple adaptations to the flower structure are included to facilitate this process.
These flowers are able to shed pollen particles directly onto the stigma. Sometimes pollination occurs before the flower opens. This also occurs in cleistogamous flowers (underground flowers).
Sunflowers, orchids, peas and tridex are plants that use autogamy during their pollination. Pollination occurs independently of external pollination agents.
Therefore, plant breeding can be achieved even in areas where pollinators are absent.
Autogamy also occurs in 3 ways- Homogamy, Cleistogamy, Bud Pollination
Benefits of self-pollination
Self-pollination is used to maintain pure lines for hybridization or hybridization experiments.
This maintains the purity of the parent character or race indefinitely.
The plant is not required to produce large numbers of pollen grains.
Flowers do not develop tools to attract insect pollens.
Self-pollination eliminates some bad residual characters.
Tools to ensure self-reproduction:
The flowers should be bisexual and both sexes mature at the same time.
In some cases, the flowers are bisexual and cleistogamous, ie, closed.
Pollination occurs in the bud position before the flower opening (anthesis).
Disadvantages of Self-pollination
New useful characters are rarely introduced.
The power and vitality of the race decrease with prolonged self-pollination.
Immunity decreases from diseases.
Variability and hence adaptability to variability are reduced.
2. Geitonogamy
It is a type of self-pollination, where pollen from the anther of one flower accumulate on stigma of another flower of the same plant. This can be achieved by a pollinator, visiting several flowers of the same plant.
As mentioned flowers using Geitonogamy depend on external pollination i.e. agents such as animals, insects, and wind . Therefore, low amounts of external pollination agents can reduce seed production in the plant.
Geitonogamy is involved in the production of genetically identical offspring.
Geitonogamy is enhanced in flowers that are situated on a single stem.
Cross Pollination
In such pollinations, the pollen is transferred from the anthers of one flower to the stigma of another flower. In this case, the two flowers are genetically distinct from each other.
Cross pollination is always dependent on another agent to cause transfer of the pollen.
Benefits of Cross-Pollination
Cross pollination is beneficial for plant race because it introduces new genes into the lineage as a result of fertilization between genetically distinct gametes.
Cross polymerization improves resistance in off-springs and resistance to changes in the environment.
If there are any residual characters in the lineage, they are eliminated as a result of genetic recombination.
Disadvantages of pollination
Pollen grains have a high waste that needs to be produced in order to ensure pollination.
Recombination of genes can lead to the elimination of good traits and unwanted characteristics can be added.
Agents of Pollination include birds, animals, water, air and insects.
Depending on the agent of pollination, cross pollination can be of the following types:
1. Hydrophilous flowers
These flowers are pollinated through water.
The flowers are often too small and inconspicuous for other agents.
There is no fragrance or too much color on their petals.
Pollen is adapted to be able to float in water.
2. Zoophilous Flowers
In this type of pollination, there are animals such as humans, bats, birds etc., as pollination agents.
Zoophilous flowers have pollen that is made to stick on the body of the animal so that they can be easily carried from one flower to another.
3. Anemophilous Flowers
These flowers are pollinated by air.
Important feature of these flowers is the wind pollinated that they are very light so that they can be easily carried by the wind.
Pollen grains are very light, non-sticky and sometimes winged.
4. Entomophilic flowers
These flowers are pollinated via insects.
These flowers are often attractive to watch with bright petals and are fragrant to attract insect visitors.
They have broad stigma or anthers.
Many of the insect-pollinated flowers secrete nectar which attracts butterflies, bees or other similar insects.
Pollen grains in Entomophilic flowers are shiny or have extensions that help them stick to the bodies of insects.
5. Ornithophilous flowers
These flowers are pollinated by birds. Very few flowers and birds show this form of pollination.
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