Q.Mention two strategies evolved to prevent self-pollination in flowers.

To promote genetic diversity and avoid inbreeding depression, flowers have evolved several strategies to prevent self-pollination. Two such prominent mechanisms are:

• Dichogamy: This refers to the asynchronous maturation of the anther and stigma. In some flowers, pollen is released before the stigma becomes receptive (protandry), while in others, the stigma becomes receptive much before the pollen is released (protogyny). This temporal separation ensures that self-pollen cannot fertilize the ovules of the same flower. …

Flowers are the reproductive structures of angiosperms, housing both male and female gametophytes. The male gametophyte, represented by the pollen grain, develops within the anthers, which are part of the stamen. The female gametophyte, or embryo sac, is contained within the ovule, located inside the ovary, which is part of the pistil (or carpel). For successful reproduction, pollen must be transferred from the anther to the stigma of a pistil, a process known as pollination.

While many flowers possess both male and female reproductive organs (they are bisexual or hermaphroditic), continuous self-pollination – where pollen from the same flower fertilizes its own ovules – can lead to a phenomenon called inbreeding depression. This results in reduced vigor, fertility, and overall fitness of the offspring over generations due to the accumulation of deleterious recessive genes. To maintain genetic diversity and ensure the health of the species, flowering plants have evolved various "outbreeding devices" or strategies to discourage self-pollination and promote cross-pollination, where pollen comes from a different plant or a different flower on the same plant.

Here are two significant strategies evolved to prevent self-pollination in flowers:

• Dichogamy: This strategy involves the anthers and the stigma of a bisexual flower maturing at different times. This temporal separation ensures that when pollen is released, the stigma of the same flower is not receptive, or vice-versa, thereby preventing self-pollination.
  • Protandry: In this condition, the anthers mature and release pollen before the stigma of the same flower becomes receptive. This is common in plants like sunflowers and cotton. By the time the stigma is ready to receive pollen, the flower's own pollen has already been dispersed, necessitating pollen from another flower.
  • Protogyny: Conversely, in protogyny, the stigma becomes receptive much earlier than the anthers of the same flower release pollen. Examples include Ficus (fig) and Aristolochia. By the time the flower's own pollen is mature, its stigma has already been pollinated by pollen from another flower, or its receptive period has passed. …