Difference Between Autogamy Geitonogamy and Xenogamy

Main Difference – Autogamy Geitonogamy vs Xenogamy

Autogamy, geitonogamy, and xenogamy are three modes of reproduction in plant breeding. Autogamy and geitonogamy are two methods of self pollination and xenogamy is the method used in cross pollination. Cross pollination is advantageous when compared to self-pollination due to the production of genetically varied offspring. The main difference between autogamy geitonogamy and xenogamy is that autogamy occurs when the pollen grains from the anther of the flower are deposited on the stigma of the same flower, while geitonogamy occurs when the pollen grains from the anther of one flower are deposited on another flower of the same plant, and xenogamy occurs when the pollen grains of one flower is deposited on the stigma of a genetically different flower in the same species.

This article explores,

1. What is Autogamy
      – Definition, Characteristics, Pollination, Examples
2. What is Geitonogamy
      – Definition, Characteristics, Pollination, Examples
3. What is Xenogamy
      – Definition, Characteristics, Pollination, Examples
4. What is the difference between Pollination vs Fertilization

What is Autogamy

Autogamy is the self-fertilization in organisms, which is the fusion of two gametes, coming from the same individual. It is especially observed in flowering plants. Hence, autogamy can be considered as the type of self-pollination, where the pollen grains from the anther of the one flower are deposited on the stigma of the same flower. Genetically identical offspring to their parents is produced by the autogamy. Flowers which use autogamy consist of several adaptations in the structure of the flower to facilitate this process. These flowers are capable of shedding pollen grains directly onto the stigma. Sometimes, pollination occurs even before the opening of the flower. Sunflowers, orchids, peas and tridax are the plants that use autogamy during their pollination. Pollination occurs independently from external pollinating agents.  Hence, plant breeding can be achieved even in areas where the pollinators are absent. However, autogamy produces less genetically diverse offspring, which is a disadvantage of this process. The orchid Ophrys apifera, containing two pollinia, which bend themselves towards the stigma is shown in figure 1.

Figure 1: Autogamy in Ophrys apifera

What is Geitonogamy

Geitonogamy is a type of self-pollination, where the pollen grains from the anther of one flower are deposited on another flower of the same plant. It can be achieved by a pollinator, visiting multiple flowers of the same plant. Geitonogamy is functionally a type of cross pollination, but genetically it is a type of self-pollination. Unisexual plants can be of two types: monoeciuos and dioecious. Monoecious plants which contain both male and female flowers in the same plant undergoes geitonogamy. As mentioned earlier, flowers using geitonogamy depend on the external pollinating agents like wind, insects, and animals. Hence, the reducing amounts of external pollinating agents may reduce the seed production in the plant. Geitonogamy is involved in the production of genetically similar offspring to parent. Geitonogamy is enhanced in flowers which are located on a single stem. Geitonogamy is shown in figure 2.

Figure 2: Geitonogamy

What is Xenogamy

Xenogamy is a type of cross pollination where the pollen grains of one flower is deposited on the stigma of a genetically different flower of the same species. Since the pollen grains belong to a genetically varied plant, cross pollination generates a genetically varied offspring. Spreading of the pollen grains requires external pollinating agents like wind, water, insects and animals. Therefore, in order to attract insects and animals to the flower, several characters like brightly colored petals, nectar and scents are exhibited by the cross pollinating flowers. Several adaptations of the flower itself prevent the self-pollination, enhancing the cross pollination. Some flowers possess mechanical barriers on the stigmatic surface like gynostegium and pollinia. This is called herkogamy. Dichogamy is the differential maturation of pollen and stigma. In some flowers, self-pollination is incapable of fertilizing the flower; this is called self-incompatibility. Some plants exhibit male sterility, where pollen grains of the plant is not functional, and only cross pollination is capable of producing seeds. Heterostyly is the production of stamens and style in different lengths. It is found in flowers of Linum and Primula. Dioecious plants with unisexual flowers use xenogamy.

Figure 3: Heterostyly

Difference Between Autogamy Geitonogamy and Xenogamy

Definition

Autogamy: Autogamy is the fertilization of a flower by pollen from the same flower.

Geitonogamy: Geitonogamy is the fertilization of a flower by pollen from another flower on the same plant.

Xenogamy: Xenogamy is the fertilization of a flower by the pollen of a flower from a genetically different plant.

Type of Pollination

Autogamy:  Autogamy is a self-pollination method.

Geitonogamy: Geitonogamy is functionally a cross pollination method but genetically a self-pollination method.

Xenogamy: Xenogamy is a self-pollination method.

Contribution to Evolution

Autogamy:  Autogamy produces a genetically identical offspring. Hence, it has no contribution to evolution.

Geitonogamy: Geitonogamy produces genetically identical offspring. Hence, it has no contribution to evolution.

Xenogamy: Xenogamy produces an offspring with genetic variations compared to the parents. Hence, it has a contribution to the evolution.

Adaptations in Flowers

Autogamy:  Autogamy flowers are capable of shedding pollen grains directly onto the stigma as well as pollinating before the opening of the flower.

Geitonogamy: Several geitonogamy flowers are located on the same stem.

Xenogamy: Herkogamy, dichogamy, self-incompatibility, male sterility, and heterostyly are the adaptations in xenogamy flowers.

Advantages

Autogamy:  Pollination can occur even without the assistance of external pollinating agents in autogamy.

Geitonogamy: Geitonogamy can maintain the parental characters of the race indefinitely.

Xenogamy: Xenogamy produces genetically modified offspring with different characters to the offspring.

Disadvantages

Autogamy:  Genetic variations of the offspring are avoided in autogamy.

Geitonogamy: Excess force should be generated in order to be pollinated by external pollinating agents.

Xenogamy: The efficiency of the seed production depends on the external pollinating agents.

Examples

Autogamy:  Sunflowers, orchids, peas and tridax are examples for autogamy.

Geitonogamy: Corn is the most common example of geitonogamy flowers.

Xenogamy: Squash, onions, broccoli, spinach, willows, grasses and olive trees are the examples of xenogamy.

Conclusion

Autogamy, geitonogamy, and xenogamy are three types of reproduction modes which are used by plants. Autogamy is a self-pollination method, where the pollen grains of the anther are deposited on the stigma of the same flower. Geitonogamy is also a self-pollination method, where the pollen grains from the anther of one flower are deposited on the stigma of a second flower on the same plant. Both autogamy and geitonogamy produce a genetically identical offspring to the parents. Xenogamy is the cross pollination method, where the pollen grains from the anther of one flower are deposited on the stigma of a flower on a different plant in the same species. Cross pollination produces a genetically varied offspring with beneficial characters. Cross pollinating flowers are capable of attracting their external pollinating agents like insects and animals to the flower by exhibiting several characters in the flower. Some flowers consist of adaptations to eliminate self-pollination as well. However, the main difference between autogamy, geitonogamy, and xenogamy is their mechanisms of pollinating the stigma of a flower.

Reference:
1. “Pollination in Plants: Types, Advantages, and Disadvantages.” YourArticleLibrary.com: The Next Generation Library. N.p., 22 Feb. 2014. Web. 27 Apr. 2017.

Image Courtesy:
1. “Ophrys apifera flower” (CC BY-SA 3.0) via Commons Wikimedia
2. “1611805” (Pixabay) via Pixabay
3. “Stigma, Stamen, Anthers” by Tess Watson (CC BY 2.0) via Flickr