Outbreeding Devices

Outbreeding is the mechanism by which plants prevent self-pollination and promote cross-pollination, enhancing genetic diversity in the population. Outbreeding devices are structural or physiological adaptations in flowers that ensure pollen from one plant fertilises another, rather than the same flower or plant. These devices are crucial in angiosperms to avoid inbreeding depression and increase genetic variability, thereby improving survival and promoting species evolution.

1.0What Are Outbreeding Devices?

• Definition: Outbreeding devices are mechanisms or features in flowers that prevent self-pollination and encourage cross-pollination.
• They act as barriers to self-fertilisation, ensuring genetic recombination between different individuals.
• These devices can be structural (physical barriers) or functional (temporal or physiological).

2.0Types of Outbreeding Devices

1. Dichogamy: Dichogamy refers to the temporal separation of male and female reproductive maturity in the same flower.

• Types:
• • Protandry: Anthers mature before the stigma.
  • • Example: Sunflower, Calotropis
  • Protogyny: Stigma matures before anthers.
  • • Example: Curcuma, Crotalaria

2. Herkogamy: Herkogamy involves the spatial separation of anthers and stigma within a flower.

• The physical distance prevents pollen from falling onto the stigma of the same flower.
• Example: Hibiscus, mustard, sunflower

3. Self-Incompatibility (SI): Self-incompatibility is a physiological mechanism where the stigma can recognise and reject pollen from the same plant.

• Controlled by S-alleles in the plant genome.
• Example: Brinjal (Solanum melongena), Petunia

4. Dichogamy + Herkogamy Combination: Some plants use both temporal and spatial separation to prevent self-pollination.

• Example: Hibiscus, which shows both stigma-anther separation and protandry/protogyny.

5. Heterostyly: Heterostyly is a structural adaptation in which flowers have different forms of styles and stamens.

• Example: Primrose (Primula) – “pin” and “thrum” flowers.
• Pollinators carry pollen from one form to the compatible form, promoting cross-pollination.

6. Dichogamy with Self-Sterility: Some plants combine temporal separation and genetic self-sterility to ensure effective outbreeding.

• Example: Papaya, Crotalaria

7. Male Sterility: Certain plants have flowers in which the male reproductive parts (anthers) are sterile, making self-pollination impossible.

• Example: Maize, sunflower hybrids

8. Other Mechanical Adaptations

• Exserted stamens and style: Ensures pollen is deposited on visiting pollinators.
• Closed flowers (cleistogamy): Some flowers remain closed until cross-pollinated by external agents, ensuring only compatible pollen is accepted.

3.0Significance of Outbreeding Devices

• Promotes genetic variation in offspring.
• Reduces inbreeding depression.
• Enhances evolutionary fitness and adaptability.
• Supports pollinator-mediated cross-pollination, crucial in angiosperm reproduction.
• Improves crop yield in agriculturally important species through hybrid vigour.

4.0Outbreeding Devices Examples