Choose the correct statements regarding self-incompatibility:
(I) Self-incompatibility is a device that encourages cross-pollination.
(II) Self-incompatibility prevents self-pollen from fertilising the ovules.
(III) Self-incompatibility ensures self-fertilisation.
(IV) Self-incompatibility encourages both self- and cross-pollination.
Choose the correct statements from those given above.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → I and II
Self-pollination over many generations leads to inbreeding depression. So flowering plants have devices that discourage self-pollination and encourage cross-pollination. Self-incompatibility is one of them. It is a genetic mechanism: the pistil stops pollen of the same plant from germinating or growing a tube.
(I) Self-incompatibility is a device that encourages cross-pollination. — True. It is one of the outbreeding devices that encourage cross-pollination.
(II) Self-incompatibility prevents self-pollen from fertilising the ovules. — True. It blocks pollen germination or pollen tube growth of self-pollen in the pistil.
(III) Self-incompatibility ensures self-fertilisation. — False. It does the opposite: it prevents self-fertilisation.
(IV) Self-incompatibility encourages both self- and cross-pollination. — False. It works against self-pollination, so it cannot encourage both.
NCERT Extract:
Outbreeding Devices – “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. … 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.”