Question

Both autogamy and geitonogamy are prevented in
(a) Papaya
(b) Cucumber
(c) Castor
(d) Maize

Answer 1

Hint In self-pollination transfer of pollen grains take place from the anther to the stigma of the genetically similar flower. In self-pollination anther and stigma mature simultaneously and pollination takes place without an external agent.

Complete Answer:
Autogamy takes place in the same flower whereas geitonogamy takes place in the different flowers of the same plant. It is shown by hermaphrodite or unisexual plants. Autogamy and geitonogamy are prevented in the case of the dioecious plant where male and female gametes lie in different plants and need an external agent for pollination. Dioecious plants show cross-fertilization.

Additional information:
Autogamy is of homogamy and cleistogamy type. In homogamy, the flower is open like chasmogamous in which both anther and stigma close together and mature simultaneously with pollen release and stigma receptivity. In cleistogamy, the flower remains closed with anther and stigma lies close to each other. Cleistogamy ensures seed set even in the absence of pollination. In some cases, the flower is chasmogamous at the beginning of the flowering season and then becomes cleistogamous to ensure fruit formation.
Self-pollination shows both advantages and disadvantages. Advantages are it produces homozygous progeny, maintains pure lines, maintains superiority, produces a large number of pollen grains and harmful effects get eliminated naturally.
Disadvantages are no new trait introduced, decrease variability and adaptability with changing environment, resistance from disease decreases with time, the recessive trait appears and shows homozygosity and yield decreases with time due to reduction in vitality.

So, the correct answer is ‘Papaya’.

Note: In some plants, self-pollination occurs when cross-pollination fails which is known as a fail-safe device. In potato, stigma bends over anther, in sunflower stigma curls back to receive pollen, and in Mirabilis jalapa anther bend over stigma for pollination.