About Lesson
Genetic Consequences of Self-Pollination
- Self-pollination leads to a very rapid increase in homozygosity. Therefore, populations of self-pollinated species are highly homozygous, self-pollinated species do not show inbreeding depression, but may exhibit considerable heterosis.
- Therefore, the aim of breeding methods generally is to develop homozygous varieties.
Mechanisms promoting cross pollination
- Dicliny: Dicliny or unisexuality is a condition in which the flowers are either staminate (male) or pistillate (female).
- a) Monoecy
- Staminate and pistillate flowers occur in the same plant, either in the same inflorescence, e.g., Castor, mango and coconut, or in separate inflorescences, chestnut, strawberries, rubber, grapes and cassava.
- b) Dioecy
- The male and female flowers are present on different plants, i.e., the plants in such species are either male or female, e.g., papaya, date, hemp, asparagus, and spinach.
- In general, the sex is governed by a single gene, e.g., asparagus and papaya. In some cases, there are hermaphrodite plants in addition to males and females, and a number of intermediate forms may also occur.
- Stamens and pistils of hermaphrodite flowers may mature at different times facilitating cross -pollination.
- a) Protogyny. In crop species like bajra, pistils mature before stamens.
- b) Protandry. in crops like Maize and sugarbeets, stamens mature before pistils.
- In Lucerne or alfalfa, stigmas are covered with a waxy film. The stigma does not
become receptive until this waxy film is broken. The waxy membrane is broken by
the visit of honey bees which also effect cross-pollination.
- A combination of two or more of the above mechanisms may occur in some species. This improves the efficiency of the system in promoting cross-pollination. For example, Maize exhibits both monoecy and protandry.
- Self-Incompatibility:
- It refers to the failure of pollen from a flower to fertilize the same flower or other flowers on the same plant.
- Self-incompatibility is of two types : sporophytic and gametophytic. In both the cases, flowers do not set seed on selfing.
- It is highly effective in preventing selfpollination.
- Male Sterility:
- Male sterility refers to the absence of functional pollen grains in otherwise hermaphrodite flowers.
- Male sterility is of two types: genetic and Cytoplasmic. Cytoplasmic male sterility is termed Cytoplasmic-genetic when restorer genes are known.