Which of the following is a mechanism to discourage self-pollination and promote cross-pollination?

Both (a) and (b) options are correct.

a- Placement of anther and stigma at different positions.

b- Non-synchronization of pollen release and stigma receptivity.

c- Both (a) and (b) options are correct is the correct option.

d- Stamen and stigma at the same height.

The majority of flowering plants have hermaphrodite flowers, where the pollen grains have the potential to come in contact with the stigma of the same flower. However, continued self-pollination in these plants can lead to a phenomenon called inbreeding depression. To counteract this, flowering plants have evolved various mechanisms to discourage self-pollination and promote cross-pollination.

One such mechanism is the asynchrony of pollen release and stigma receptivity. In some species, the timing of pollen release and stigma receptivity is not synchronized. This means that either the pollen is released before the stigma becomes receptive or the stigma becomes receptive much earlier than the release of pollen. This temporal separation prevents self-pollination by ensuring that the pollen from the same flower cannot fertilize its own stigma.

Another mechanism is the spatial separation of the anther and stigma within the flower. In certain species, the anther (which produces pollen) and the stigma (which receives pollen) are positioned at different locations within the flower. This physical separation prevents the pollen from coming into direct contact with the stigma of the same flower, reducing the chances of self-pollination.

Additionally, plants employ self-incompatibility, a genetic mechanism that prevents self-pollen from fertilizing the ovules. This mechanism inhibits the germination of self-pollen or the growth of pollen tubes in the pistil, effectively preventing self-pollination.