Question

What is self- sterility?

Answer 1

Self- sterility is also known as self- incompatibility and is usually used in context with plants. The term ‘sterile’ means inability to reproduce through sexual reproduction and produce a progeny, especially through natural methods. It has the advantage of preventing inbreeding depression in organisms.

Complete answer:
The term ‘self-sterile’ is used for describing plants which fail to set self-seed when they are grown in isolation or when they are self-pollinated. There are several examples by which plants make themselves sterile in order to prevent self-pollination. The features of plants which discourage self-pollination and encourage cross-pollination in order to bring some genetic variability are called Outbreeding devices. They prevent the loss of genetic variation or inbreeding depression which may be a result of continued self pollination. Examples of such devices include:
Unisexuality: Formation of unisexual flowers. This is also known as dicliny. This can be seen in Monoecious plants like Castor and Maize or this can be seen in Dioecious plants like Vallisneria and Papaya.
Dichogamy: This refers to the different maturation time of androecium and gynoecium in the same flower. Either the pollen is released before the stigma becomes receptive, a condition known as Protandry or the stigma becomes receptive much before the release of pollen, a condition known as Protogyny.
Self-incompatibility or self- sterility: It refers to the failure of the pollen grains from fertilizing the ovule by inhibiting pollen germination of pollen tube growth in the pistil. It is a genetically controlled mechanism.
In some species, the anther and stigma are placed at different positions so that pollen cannot come in contact with the stigma of the same flower.

Note:
Some plants that show self-sterility are Lotus, Orchids, and members of the Fabaceae family. Incomplete dichogamy is shown in Mirabilis jalapa. Heterostyly is a mechanism to prevent self-fertilisation by having a longer stigma and shorter stamen or vice versa. Heterostyly is mostly seen in flowers with actinomorphic symmetry.