Self-Incompatibility in Plants

Study Notes

Pollination is the transfer of pollen grains from the anther to the stigma of a flower.
There are two types of pollination: self-pollination and cross-pollination.

Self-pollination is the transfer of pollen grains from the anther to the stigma of the same flower.
It can occur in bisexual flowers or in unisexual flowers where both male and female flowers are borne on the same plant.
Advantages of self-pollination:
- It is a surer process in bisexual flowers where stamens and carpels mature at the same time.
- Parental characters are preserved.
- There is no wastage of pollen grains.
- The flowers need not be large and showy.
Disadvantages of self-pollination:
- Continued self-pollination may lead to weakening of the variety or species.
- The seeds produced are poor in quality and give less vigorous offspring.
- It does not yield new varieties.

Cross-pollination is the transfer of pollen grains from the anther of one flower to the stigma of another flower of the same species.
Advantages of cross-pollination:
- The offspring are healthier.
- The seeds produced are abundant.
- New varieties may be produced by cross-pollination.
Disadvantages of cross-pollination:
- It requires an external agent (wind, water, insect) to be present.
- The pollinating agent may not be available at the right time.
- The pollen quantity may not be sufficient.

Insects: insects like bees and butterflies are common agents of cross-pollination.
Wind: wind is another common agent of cross-pollination.
Water: water-pollinated flowers are found in aquatic plants.
Birds: some flowers are pollinated by birds.

Fertilization occurs when a pollen grain reaches the stigma and germinates, producing a pollen tube.
The pollen tube grows down through the style and into the ovary, where it fertilizes an egg cell.
The fertilized egg cell develops into a zygote, which then grows into a seed.
The process of fertilization is essential for the reproduction of flowering plants.### Differences between Wind-Pollinated and Insect-Pollinated Flowers
Wind-pollinated flowers have dull colors, no fragrance, and produce large amounts of pollen grains that are light, smooth, and small.
Insect-pollinated flowers are brightly colored, fragrant, and secrete nectar, with fewer pollen grains produced that are larger, sticky, and spiny.

Elephophily is a type of pollination involving elephants
Found in Rafflesia, a rare flower that grows at the feet of elephants
Pollen grains get stuck to the elephant's feet and are carried to other similar flowers

Artificial pollination is the transfer of pollen to the stigma by humans
Practiced by plant breeders and scientists to evolve new varieties
Involves emasculation (removing anthers) and bagging (covering flowers with plastic bags)