Difference between Allogamy and Xenogamy

What is Allogamy?

The pollens from male reproductive organs of the plant are transferred to female reproductive organs. This process is known as pollination. Pollination is further classified as self-pollination and cross pollination[1].

When the flower is fertilized from pollens originating from same flower, it is called self-pollination. The major advantage of self-pollination is that it maintains purity of a plant indefinitely. Whereas in cross pollination, flower is fertilized from pollens originating from a different flower. Cross pollination has an evolutionary advantage as it combines genetic traits of both the parents. This increases the genetic diversity and also the fitness of the plant. Cross-pollination is also known as allogamy[2].

The term allogamy is derived from Greek word alios “meaning other” and gamos “meaning wedding”. In this process, the pollens used to fertilize a flower, either belong to a same plant or to a different plant within the same species. Allogamy includes Geitonogamy and Xenogamy.

What is Xenogamy?

The word Xenogamy comes from a Greek word Xenos “meaning stranger” and gamos “meaning wedding”. In xenogamy, the flowers are pollinated from pollens originating from a genetically different plant within the same species. As a result, xenogamy always produces genetically modified offspring’s. The main floral characteristics that promote xenogamy include herkogamy, dichogamy, self-incompatibility, male sterility, heterostyly etc[3].  The plants relying on xenogamy as means of pollination, produce brightly colored petals, scents and nectar for attracting cross pollinators.

Another form of cross pollination is Geitonogamy. The word Geitonogamy comes from a Greek word geiton “meaning neighbor” and gamy “meaning wedding”. In this case, the flower is fertilized from pollens originating from a different flower within the same plant. The outcome of this form of cross pollination is genetically similar to autogamy [4].

What are the differences between Allogamy and Xenogamy?

1. Method of Pollination:

In the allogamy, the fertilization occurs from pollens of same plant. In Xenogamy, the fertilization occurs from pollens of different plants from the same species. The pollination is not from the same plant.

2. Pollinating Agents:

In allogamy, the external pollinating agents are not needed. In case of Xenogamy, the external pollinating agents are absolutely required.

3. Fertilization with genetically different pollen:

In allogamy, the genetically different pollen is not used for pollination. On the other hand, in Xenogamy, the pollens that are used to pollinate a flower belong to a genetically different and non-identical plant of the same species.

4. Genetically modified off-springs:

The off-springs as a result of allogamy are not genetically modified and are of the same genetic identity as that of the parent flowers. In case of Xenogamy, the off-springs are genetically modified and are very different from their parent flowers [5].

5. Need of attracting pollinators:

The plants that rely on xenogamy as their means of pollination produce brightly colored petals, scents and nectar for attracting birds and insects. There is a competition to attract pollinators. But the plants that rely on Allogamy have no such requirements.

6. Resistance to disease:

The resistance to diseases for the plants which pollinate by Xenogamy are much better than the plants which pollinate through Allogamy. The genetic modification of the off-springs selects for the better disease resistance in Xenogamy.

7. Corn is an example of Allogamy whereas broccoli, papaya and cucurbits pollinate through Xenogamy.

The differences between Allogamy and Xenogamy described above are summarized in a tabular form below.

To conclude, the important points of difference between allogamy and xenogamy can be summarized as followsConclusions

1. In allogamy, the fertilization occurs from the pollen of same plant, whereas in xenogamy, the pollination occurs from different plants.
2. External pollinators are not required in case of allogamy but xenogamy needs external pollinators.
3. In Allogamy, the fertilization takes place with genetically different pollen whereas the pollens used in xenogamy are from a genetically different but same species flower.
4. Allogamy does not produce genetically modified off-springs whereas in xenogamy the off-springs are genetically different from the parents. In other words, allogamy preserves the parent’s genetic makeup, xenogamy does not.
5. In allogamy, the cells do not need to attract pollinators but xenogamous plants use bright colored petals, scents and nectars to increase the chance of fertilization.
6. Xenogamy leads to more resistance to diseases than allogamy but to the genetic mixing.
7. A common example of allogamy is corn, an example of xenogamy is broccoli.