Fruit and Seed Formation Without Fertilization

Fruits and seeds are not only essential  in the life cycle of flowering plants; they are also utilized as sources of food. In a few species, special mechanism has evolved to produce seed and fruit. For example: Asteraceae. What are the different type of special mechanisms? What is meant by apomixis and parthenocarpy? What is parthenocarpy?

Apomixis
Apomixis is a type of asexual reproduction that mimics sexual reproduction to produce seeds in flowering plants. Two types of apomixis are found in flowering plants. These are as follows:

  1. An unfertilized diploid egg developing into the embryo through parthenogenesis. Example: Rosaceae
  2. Embryo arising directly from the nucellar cells of the ovule. Example: Citrus

Polyembryony

Polyembryony may be defined as the phenomenon of more than one embryo developing from a single ovule. It was discovered by Leeuwenhook. Polyembryony occurs commonly in many animals and plants, Example: Nine-banded armadillo. Polyembryony is classified into two types. These are as follows:

  1. True polyembryony – More than one embryo develops from single ovule. Example: Citrus
  2. False polyembryony – More than one embryo develops from different ovule. Example: Mango

Parthenocarpy

Parthenocarpy may be defined as the production of fruit from an unfertilized egg. It can be achieved by naturally or artificially. Example: seedless watermelon.

Two types parthenocarpy are found. These are as follows:

  1. Stimulative parthenocarpy – In this process, pollination is required to produce fruits. Example: Seedless watermelons.
  2. Vegetative parthenocarpy – In this process, pollination is not required to produce fruits. Example: Seedless cucumbers.

Hybrid cultivation of fruits by parthenocarpy is used to increase the productivity. But, parthenocarpy process is expensive. As a result, hybrid seeds and fruits become too expensive.

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