Read the passage and answer the following questions.

Flowering plants employ various mechanisms to discourage self-pollination and promote cross-pollination. These mechanisms include temporal separation of pollen release and stigma receptivity, spatial separation of anther and stigma, self-incompatibility, and the production of unisexual flowers. In some species, the timing of pollen release and stigma receptivity is not synchronized. This prevents self-pollination as either the pollen is released before the stigma becomes receptive or the stigma becomes receptive before the pollen is released. Similarly, in other species, the anther and stigma are positioned in a way that prevents self-pollination by avoiding contact between the pollen and stigma of the same flower. Self-incompatibility is a genetic mechanism that prevents self-pollen, whether from the same flower or other flowers of the same plant, from fertilizing the ovules. It achieves this by inhibiting pollen germination or pollen tube growth in the pistil.The production of unisexual flowers is another device to prevent self-pollination. For example, in plants like castor and maize, which are monoecious, having both male and female flowers on the same plant prevents self-pollination (autogamy) but not pollination between flowers on the same plant (geitonogamy). On the other hand, in species like papaya, male and female flowers are present on different plants (dioecy), effectively preventing both autogamy and geitonogamy.During pollination, the pistil may encounter pollen of the wrong type, either from other species or from the same plant if it is self-incompatible. The pistil has the ability to recognize whether the pollen is of the right type (compatible) or the wrong type (incompatible). If the pollen is compatible, the pistil accepts it and promotes post-pollination events leading to fertilization. However, if the pollen is incompatible, the pistil rejects it by preventing pollen germination on the stigma or pollen tube growth in the style.The recognition and acceptance or rejection of pollen by the pistil involve a continuous dialogue between the pollen grain and the pistil. This dialogue is facilitated by chemical components present in both the pollen and pistil. In recent years, scientists have made progress in identifying some of these components and understanding the interactions that lead to the recognition, acceptance, or rejection of pollen by the pistil.

Which mechanism is NOT used by flowering plants to discourage self-pollination?

Synchronized timing of pollen release and stigma receptivity

The correct answer is Option (4)- Synchronized timing of pollen release and stigma receptivity

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. 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.

In some other species, the anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower. Both these devices prevent autogamy.

The third device to prevent inbreeding is self-incompatibility. This is a genetic mechanism and prevents self-pollen (from the same flower or other flowers of the same plant) from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil.

Another device to prevent self-pollination is the production of 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, that is each plant is either male or female (dioecy). This condition prevents both autogamy and geitonogamy.