Pollination, or the transport of pollen from the anther to the stigma of a blooming plant, is how fertilisation happens in flowering plants. The pollen tube carries the male gametes (sperm cells) that are transmitted into the female gametophyte (i.e. ovules of flowering plants and cones of coniferous plants). When it comes to pollination, the ovum can be fertilised by either cross-pollination or self-pollination.

Cross-pollination is a type of fertilisation in which sperm from one plant’s pollen (anther) is transmitted to the stigma of another plant’s flower.

Cross-pollination produces more new genotypes than self-pollination. It contributes to increased genetic diversity. It also avoids inbreeding depression, which occurs when the biological fitness of a population is diminished due to inbreeding. As a result, it reduces the likelihood of a plant species having offspring that are susceptible to disease or have genetic disadvantages due to unfavourable recessive genes.

What is Pollination?

Pollination is the process of transferring pollen grains from the anther to the stigma before fertilisation. Male and female gametes in flowering plants are both non-motile. This requires the employment of a vector. Pollination is the process of bringing together male and female gametes in order to achieve fertilisation. There are two kinds of pollination: self-pollination and cross-pollination. Pollination between the same species is essential for pollination to be successful.

What is Cross Pollination?

Cross-pollination is also called heterogamy. It is a type of pollination in which the sperm-laden pollen grains are transmitted from one plant’s cones or flowers to another’s egg-bearing cones or flowers. Cross-pollination occurs in both angiosperms (flowering plants) and gymnosperms (cone-bearing plants), and it helps in cross-fertilization and outbreeding. Pollen transportation can occur by wind, as in conifers, or through symbiotic interactions with various creatures (e.g., bees and some birds and bats) that transport pollen from plant to plant while feeding on nectar.

Types of Cross Pollination

Wind, water, air, birds, animals, butterflies, and other elements all contribute to cross-pollination. The many forms of cross-pollination are explained further below.

1. Anemophily: Anemophily is the pollination of plants by wind. Anemophily is used by the little, odourless, greenish flowers to cross-pollinate. Plants in this area do not attract other pollinators since they do not produce beautiful flowers with nectars, hence wind is the sole pollinator that spreads pollen grains. Flowers that pollinate by wind feature light and free-swinging anthers, which aids in pollination by air. Palm, coconut, maize, and other plants that pollinate by wind are examples.
2. Zoophily: zoophily is the use of animals to pollinate plants. Animals play an important role in seed dispersion here. Animals travel to various regions after consuming the plant’s fruit. They disseminate the seeds by moving. There are three types of zoophily:

• Ornithophily is the practice of pollinating plants with the assistance of birds.
• Entomophily is the use of insects to pollinate plants.
• Chiropterophily is the pollination of plants by bats.

3. Hydrophily

Hydrophily is the use of water to pollinate plants. The pollen grains are carried by the currents of streams and rivers. There are two ways for pollination to occur in water.

• Surface Pollination: As the name implies, pollen grains float on the water’s surface and are transmitted to the stigma.
• Submerged Pollination: Submerged pollination occurs when pollen grains drop into the water and attach to the stigma.

Factors Encouraging Cross pollination

The factors promoting cross pollination are given below:

1. Dichogamy: In bisexual flowers, the stamens and pistils develop at separate rates (Anther and stigma of bisexual flowers mature at different times). They are classified into two types: a. Protogyny: Stigma becomes receptive to stamens sooner. For example, Bajra. b.Protogyny: Anther Dehisce and release pollen grains before the stigma of the same flower reaches receptivity. For example, carrots with marigolds.
2. Unisexuality: Flowers in certain plants are unisexual and grow on various plants.

Cross pollination is the sole option in this circumstance. Palms and papaya are examples.  The male and female flowers of certain plants vary but grow on the same plant.  For example, cucumbers.

3. Male Sterility: Seeds are not set because functional pollen grains are not present. Male sterility is influenced by a. genetic factors (E.g.Tomato, barley, Brinjal and Rice). b.  Cytoplasmic factors (for example, onion), and (iii) Interaction (E.g.Chilli, etc.)
4. Self incompatibility: Both male and female gametes are viable, however seeds are not generated when selfed due to specific opposing elements, yet they can set seeds when cross pollinated.

Example: Tobacco, Mango, Tomato, Mustard, Radish, Cabbage, and so forth.

4. Mechanical and structural barrier:  There are certain plants in which pollen grains from the same flower do not reach the stigma. In Pansy flowers, a hood enclosing the stigma works as a mechanical barrier.
5. Heterostyly – There are two or three varieties of flowers with varying styles (and stamens), I diheterostyly (Dimorphic Heterostyly). There are two kinds of flowers: pin-eyed (long style and 1 short stamen) and thrum-eyed (short style and long stamens), for example, Primula (Primrose), Jasmine, and (ii) Triheterostyly. There are three sorts of flowers with varying stanens heights (medium and short, long and short, long and medium), and different style heights (long, medium, and short), for example, Lythrum.

Pollination happens when anthers and stigmas of the same height come into contact.

Cross-Pollination Advantages and Disadvantages

Advantages

• The seeds that result from cross-pollination are of high grade.
• For unisexual plants, the technique of reproduction is cross-pollination.
• Cross-pollination aids in the removal of recessive traits through genetic recombination.
• Plants that reproduce by cross-pollination become more immune.
• The presence of genetic variation is due to the fertilisation of genetically diverse gametes.

Disadvantage

• Agent interdependence is unavoidable.
• A large volume of pollen is thrown away.
• Flowers must use energy to produce nectar and colour in order to attract pollinators.

Conclusion 

Pollination, or the transport of pollen from the anther to the stigma of a blooming plant, is how fertilisation happens in flowering plants. The pollen tube carries the male gametes that are transmitted into the female gametophyte (i.e. ovules of flowering plants and cones of coniferous plants). Cross-pollination is a type of fertilisation in which sperm from one plant’s pollen is transmitted to the stigma of another plant’s flower. Pollination is the process of transferring pollen grains from the anther to the stigma before fertilisation. Anemophily is the pollination of plants by wind. Chiropterophily is the pollination of plants by bats. The seeds that result from cross-pollination are of high grade. For unisexual plants, the technique of reproduction is cross-pollination.