Explain what are outbreeding devices. Give its importance

Explanation

Majority of flowering plants produce hermaphrodite flowers and pollen grains are likely to come in contact with the stigma of the same flower. Continued self-pollination result in inbreeding depression. Flowering plants have developed many devices to discourage self pollination and to encourage cross pollination.
(i) In some species Pollen release and stigma receptivity are not synchronised. Either the pollen is released before the stigma becomes receptive or stigma becomes receptive much before the release of pollen it e.g. palms
(ii) Arrangement of anther and stigma at different positions: The anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower e.g. Primula. Both these devices prevent autogamy.

(iii) Self-incompatibility: This is a genetic mechanism and prevents self pollen from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil. eg. malva.
(iv) Production of unisexual flowers: To prevent self pollination it produces unisexual flowers. If both male and female flowers are present on the same plant such as castor and maize (monoecious) it prevents autogamy but not geitonogamy. In several species such as papaya male and female flowers are present on different plants. i.e, each plant is either male or female (dioecy)