Mention two strategies evolved to prevent self-pollination in flowers.
Flowering plants have evolved several strategies to prevent self-pollination:
1. Self-incompatibility: This is a genetic mechanism that prevents self-pollen from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil.
2. Production of unisexual flowers: In some species, male and female flowers are present on different plants (dioecious condition, e.g., papaya), which prevents both autogamy and geitonogamy.
(Other strategies include: non-synchronisation of pollen release and stigma receptivity, and placement of anther and stigma at different positions.)
Explanation
The textbook describes multiple outbreeding devices that flowering plants have developed to discourage self-pollination and encourage cross-pollination. The question asks for any two strategies. The main devices mentioned are: (1) Self-incompatibility - a genetic mechanism, (2) Unisexual flowers - monoecious or dioecious condition, (3) Non-synchronised pollen release and stigma receptivity, and (4) Different positioning of anther and stigma. Students can mention any two of these strategies.
Solution Steps
Step 1: Identify the outbreeding devices mentioned in the textbook
Step 2: Select any two strategies and explain them briefly with key terms highlighted