- Self-pollination is the transference of pollen grains from the anther of a flower to the stigma of either the same or genetically similar flower.
- It is generally not dependent on any external agency for pollination.
- It is of two types:
- It is the transfer of pollen grains from anther of a bisexual flower to its stigma.
- Both stamens and carpels mature at the same time.
- It occurs in several cereals (wheat, rice), some peas and flower which do not open.
- It is kind of self-pollination where flowers could be bisexual or unisexual but are borne by the same parent plant.
- The pollens from one flower deposited on the stigma of another flower borne on the same plant.
- It may require an external agency like insects or wind.
- Self-pollination may occurs when the flowers are open (chasmogamy) or closed (cleistogamy).
- Chasmogamous self-pollination occurs only when their anthers and stigma mature at the same time (homogamy).
- The self-pollinated flowers are generally small, inconspicuous, colourless, odourless, and nectarless.
- Self-pollination occurs by following methods:
- In this case the anthers and stigmas of a bisexual flower mature simultaneously.
- The pollen grains reach the mature stigma either by contact, wind, gravity, rain drop or even insects.
- Self-pollination brought about by contact is called direct autogamy and remaining agencies perform indirect autogamy.
i) Direct autogamy
- It is accomplished by the movement of floral parts on account of growth, bending or folding.
- In Convolvulus, Ixoza, Catharanthus and Gardenia the anthers are borne at the mouth of the corolla tube.
- With the growth of style the stigma comes in contact with the ripe anthers and pollination occurs.
- Pollination takes place in Cotton when the stigma in being pushed out of the staminal tube due to the growth of the style.
- In Mirabilis, the filaments of ripe anthers bend and bring in contact with stigma.
- A similar curling of style takes place in potato.
- The stigma of Sunflower has brushing hair which helps in pushing the pollen grains from the synantherous tube.
- The stigma curls back and receives the pollen grains present on the brushing hair.
- The closing of flowers at night performs self-pollination in Argemone mexicana.
ii) Indirect autogamy
- It occurs without coming contact of anthers and stigmas.
- The pollen grains reach the stigma by rain (e.g. Caltha) or gravity (e.g. Lilac).
- In Lilac, the anthers lie exactly above the stigmas.
- The pollen grains of the dehisced anthers fall over the low lying stigmas under the influence of gravity.
- In Sanicula, male and female flowers grow side by side.
- The long style of the female flower bends over the male flowers to get pollinated.
- It occurs in bisexual flowers which are always closed.
- Such closed flowers can perform only self- pollination.
- It is generally accompanied by geocarpy when the fruits are formed underground, e.g. Groundnut.
- The phenomenon of having both open and closed flowers is called chasmocleistogamy.
Advantages of Self-pollination
- It does not depend on the external agency, so it is a sure method of pollination.
- Some flowers e.g. Oxalis utilize self-pollination for seed production when cross-pollination fails. Pollen grains are not wasted.
- Parental characters can be preserved by this pollination.
- It causes no genetic variations and because of this property, it maintains the purity of the races from generation to generation.
- It is utilized in production of homozygous parents for experimental hybridization and evolving useful varieties.
Disadvantages of Self-pollination
- It produces weak progenies, generation after generation, which cannot adapt to the changing environment.
- It does not help in evolution of new species, as it does not cause any variability.
- It cannot give any new character or new ability to the plant.
- Useful characters cannot be introduced by this method.
- The undesirable and defect characters do not get eliminated from a plant.
- The immunity of race towards infection decreases. Thus, the plants become susceptible to many diseases.