22. In certain plants, the mechanism where timing of anther dehiscence and stigma receptivity do not coincide to avoid self-pollination is called
    (1) dichogamy (2) herkogamy
    (3) monoecy (4) Dioecy

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Introduction

Plants have evolved various mechanisms to avoid self-pollination, ensuring genetic diversity through cross-pollination. One such mechanism is dichogamy, involving temporal separation in the maturity of male and female reproductive organs within a flower. This phenomenon contrasts with spatial separation mechanisms like herkogamy, and with the distribution of sexes in monoecious and dioecious plants.

What is Dichogamy?

• Dichogamy is the temporal separation of male and female reproductive phases in the same flower.

• It involves either protandry where anthers mature and shed pollen before the stigma becomes receptive, or protogyny where the stigma is receptive before pollen release.

• This timing difference reduces the chance of self-pollination and promotes outcrossing, enhancing genetic variation.

Comparison with Other Mechanisms

• Herkogamy: Spatial separation of anthers and stigma within the same flower to reduce self-pollination.

• Monoecy: Separate male and female flowers are borne on the same plant.

• Dioecy: Male and female flowers are on separate plants, making individual plants either male or female.

Biological Importance

• Dichogamy helps prevent inbreeding depression by limiting pollen from the same flower fertilizing the ovules.

• It is observed widely in flowering plants and is a key floral adaptation maintaining outcrossing strategies.

• It influences pollination ecology, floral longevity, and reproductive success.

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Summary Table: Mechanisms Preventing Self-Pollination

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Conclusion

The mechanism in which the timing of anther dehiscence and stigma receptivity do not coincide to avoid self-pollination is dichogamy. It is a temporal strategy in flowering plants promoting cross-pollination.