Question

What is pollination? Discuss mechanism favoring self and cross-pollination in crop plants.

Hint:

Remember: Self-pollination mechanisms include bisexuality, cleistogamy, homogamy while cross-pollination mechanisms include dichogamy, self-incompatibility, unisexuality, and herkogamy. Plants evolve these adaptations based on their reproductive strategy and environmental conditions.

Answer 1

Part 1: What is Pollination?
Step 1: Understanding the Question
This part asks for the definition of pollination.
Step 2: Detailed Explanation
Pollination is a fundamental process in the reproduction of flowering plants. It is defined as the transfer of pollen grains from the anther (the male part of a flower) to the stigma (the female part of a flower). This transfer is essential for fertilization to occur, which leads to the development of seeds and fruits.
Part 2: Mechanisms Favoring Self and Cross-Pollination
Step 1: Understanding the Question
This part requires a discussion of the adaptations or mechanisms that plants have evolved to promote either self-pollination or cross-pollination.
Step 2: Detailed Explanation
Mechanisms Favoring Self-Pollination (Autogamy):

Bisexuality (Hermaphroditism): The presence of both male (stamen) and female (pistil) parts in the same flower, which is a prerequisite for self-pollination. (e.g., Wheat, Rice).

Homogamy: The anthers and stigma of a flower mature at the same time, ensuring that pollination can occur.

Cleistogamy: The flowers never open, forcing self-pollination to occur within the closed bud. This is a surefire mechanism for selfing. (e.g., Groundnut).

Mechanisms Favoring Cross-Pollination (Allogamy):

Unisexuality (Dicliny): The flowers are either male or female. If male and female flowers are on different plants (dioecy, e.g., Papaya), cross-pollination is mandatory. If they are on the same plant (monoecy, e.g., Maize), it still encourages cross-pollination.

Dichogamy: The anthers and stigma mature at different times. If anthers mature first (protandry, e.g., Sunflower), or if the stigma matures first (protogyny, e.g., Bajra), it prevents self-pollination.

Self-Incompatibility: A genetic mechanism where the pollen from a flower is unable to fertilize the ovules of the same flower. The stigma chemically rejects its own pollen. (e.g., Mustard, Apple).

Step 3: Final Answer
Pollination is the transfer of pollen from anther to stigma. Mechanisms favoring self-pollination include bisexuality and cleistogamy. Mechanisms favoring cross-pollination include unisexuality, dichogamy, and self-incompatibility.