2.2 Pollination: The Transfer of Life

Introduction: What is Pollination?

  • Definition: Transfer of pollen grains from the anther (male) to the stigma (female) of a flower.
  • Purpose: Essential step for fertilization, leading to seed and fruit production.

Types of Pollination

1. Self-Pollination (Autogamy)

  • Explanation: Pollen transfer to stigma of the same flower or another flower on the same plant.
  • Examples: Pea, Wheat, Rice.
  • Advantages: Certainty, less pollen wastage, preserves parental characters.
  • Disadvantages: No new varieties, reduced vigor, increased disease susceptibility.

Types of Pollination (Continued)

2. Cross-Pollination (Allogamy)

  • Explanation: Pollen transfer from a flower on one plant to a flower on another plant of the same species.
  • Examples: Apple, Rose, Maize.
  • Advantages: New varieties, increased vigor, better adaptation.
  • Disadvantages: Uncertainty, high pollen wastage, potential for undesirable characters.

Agents of Pollination

  • External agents (abiotic or biotic) transfer pollen.

1. Pollination by Insects (Entomophily)

  • Features of Flowers: Large, bright, scented, nectar-producing, sticky/spiny pollen, sticky stigma.

2. Pollination by Wind (Anemophily)

  • Features of Flowers: Small, inconspicuous, no scent/nectar, large quantity of light/dry pollen, feathery stigmas, well-exposed stamens.

Agents of Pollination (Continued)

3. Pollination by Water (Hydrophily)

  • Features of Flowers: Small, inconspicuous, no scent/nectar, protected/light pollen, long/sticky stigmas.
  • Examples: Vallisneria, Hydrilla.

How Nature Favors Cross-Pollination (Outbreeding Devices)

  1. Unisexuality (Dicliny): Plant bears only male or female flowers (e.g., Papaya).
  2. Dichogamy: Anther and stigma mature at different times.
    • Protandry: Anthers mature first (e.g., Sunflower).
    • Protogyny: Stigma receptive first (e.g., Magnolia).
  3. Self-Sterility (Self-Incompatibility): Pollen from same flower cannot germinate on its stigma (genetic mechanism).
  4. Herkogamy: Physical barriers between anther and stigma.