Introduction
Most flowering plants produce hermaphrodite flowers, which contain both male and female reproductive parts. In such flowers, self-pollination may easily occur because pollen grains can reach the stigma of the same flower.
Continuous self-pollination leads to inbreeding depression, which causes weak offspring and reduces genetic variation.
To avoid self-pollination and encourage cross-pollination, flowering plants have developed several special mechanisms called outbreeding devices.
What are Outbreeding Devices?
Outbreeding devices are special adaptations in flowering plants that:
Prevent self-pollination
Encourage cross-pollination
Increase genetic variation
Produce healthy offspring
Types of Outbreeding Devices
1. Dichogamy (Different Timing of Maturity)
In some plants, pollen release and stigma receptivity do not occur at the same time.
Two conditions may occur:
Pollen is released before stigma becomes receptive
ORStigma becomes receptive before pollen release
This prevents pollen from fertilizing the same flower.
Importance
Prevents autogamy (self-pollination within same flower)
Encourages cross-pollination
Examples
Sunflower
Salvia
2. Herkogamy (Different Position of Anther and Stigma)
In some flowers, the anther and stigma are placed at different positions.
Because of this arrangement, pollen grains cannot easily reach the stigma of the same flower.
Importance
Prevents self-pollination
Promotes cross-pollination
Examples
Hibiscus
Gloriosa
3. Self-Incompatibility
Self-incompatibility is a genetic mechanism in plants.
In this mechanism, pollen grains from the same flower or same plant fail to fertilize the ovule.
This happens because:
Pollen does not germinate
ORPollen tube growth is stopped inside the pistil
Importance
Prevents inbreeding
Encourages cross-pollination
Examples
Brassica
Petunia
4. Unisexuality
Some plants produce separate male and female flowers.
This helps in preventing self-pollination.
Unisexuality is of two types:
a) Monoecious Condition
In monoecious plants:
Male and female flowers are present on the same plant
This condition:
Prevents autogamy
Does not prevent geitonogamy
Examples
Castor
Maize
Coconut
b) Dioecious Condition (Dioecy)
In dioecious plants:
Male and female flowers are present on different plants
One plant is only male
Another plant is only female
This condition:
Prevents both autogamy and geitonogamy
Examples
Papaya
Date Palm
Inbreeding Depression
Continuous self-pollination causes inbreeding depression.
Effects of Inbreeding Depression
Weak plants
Reduced fertility
Poor growth
Lower resistance to diseases
Cross-pollination helps to overcome these problems.
Summary Table
| Outbreeding Device | Main Function | Example |
|---|---|---|
| Dichogamy | Different timing of pollen release and stigma receptivity | Sunflower |
| Herkogamy | Different position of anther and stigma | Hibiscus |
| Self-incompatibility | Prevents self-fertilization genetically | Brassica |
| Monoecy | Male and female flowers on same plant | Maize |
| Dioecy | Male and female flowers on different plants | Papaya |
Outbreeding devices are important adaptations in flowering plants that prevent self-pollination and promote cross-pollination. These mechanisms increase genetic variation, improve plant health, and help plants survive better in changing environments.
No comments:
Post a Comment