Question

Explain outbreeding devices in angiospermic plants.

Answer 1

Plants have some mechanisms by which they tend to avoid self-pollination as continuous self-pollination leads to inbreeding depression and outbreeding leads to cross pollination.

Complete answer:
The plants have several systems that they employ, called as outbreeding devices, to facilitate cross-pollination.
In angiosperm plants, outbreeding devices that facilitate cross-pollination are:

Dicliny: Flowers are unisexual and cannot be self-pollinated. The plants can be single, which means they have the flowers of both male and female (e.g. maize) or dioecious which is to have the flowers of both male and female on separate plants (e.g., mulberry and papaya).

Prepotency: Another flower's pollen grain germinates more quickly by stigma than the same flower's pollen grain (such as apple and grape).

Self-sterility: The pollen of a flower does not germinate on the same flower stigma because the same sterile genes are present.

Herkogamy: Natural obstacles prohibit the same-floral pollens from pollinating the same-floral ovary.

Heterostyly: The anther and stigma occur at various floral levels which prevents self-pollination and fertilization.

Dichogamy: The male and female reproductive part matures at different times, thereby preventing self-pollination. Dichogamy may be further divided into two, depending on who matures first:
- Protandry: Androecium matures before gynoecium in this type. Example of this type is maize plant.
- Protogyny: The Gynoecium matures in this type earlier than the Androecium.

Note: Continual inbreeding or self-fertilization results in a condition known as inbreeding depression. Homozygous genes that are not as vital as lead to unhealthy offspring are characteristic for these conditions. As both male and female flowers have the same genes in self-pollination, no genetic variation can be seen necessary for a better and more productive birth. Most plants therefore have a number of mechanisms to avoid self-pollination and encourage cross-pollination. Outbreeding devices are plant monitoring and adjustment mechanisms for preventing self-pollination.