Polyembryony

polyembryony is the phenomenon of getting/formation of more than one embryo during the development of seed. While polyembryony, generally occurs during seed development, Rao (1965) has founded  polyembryony to develop during seed germination in Vanda caused by cleavage of apical promeristem of the single embryo.

Context 

1. Type Of Polyembryony
2. Potential Of Apomictic Polyembryony

1. Type Of Polyembryony

Polyembryony has been discovered by Leeuwenhoek (1719) at the case of Citrus. it is of three types that were :-  simple, cleavage and adventitive.

 (i) Simple Polyembryony.

 It is due to fertilization of more than one egg cell in an ovule. The condition develops when an embryo sac contains more than one egg cell or the ovule possesses more than one embryo sac, e.g., Casuarina, Citrus, Poa.

(ii) Cleavage Polyembryony.

 It is caused by splitting of proembryo into two or more parts and branching of proembryo. Another reason of cleavage is the splitting of suspensor. It is common in conifers (e.g., Pinus). Amongst all angiosperms cleavage the polyembryony is recorded in orchids.

(in) Adventive Polyembryony.

 It is formation of additional embryos from different parts of ovule (other than egg of the embryo sac) like synergids, antipodal cells, nucellus, integuments, etc. (e.g., Citrus, opuntia, Mangifera, Trillium, Onion, Groundnut).

2. Potential Of Apomictic Polyembryony 

1. Adventive embryos are fully viable.
2. Apomictic embryos are free from infection.
3. Adventive embryos are true clones of their parents.
4. The phenomenon can be used to maintain hybrid varieties indefinitely. Hybrid varieties are preferred by agriculturists because of their higher yield, vigour and resistance to stresses. They have tremendously increased crop productivity, e.g. Maize, Tomato, Cauliflower, Sorghum, Pearl Millet. However, there is one major defect in using hybrid varieties. Hybrid vigour is not maintained beyond single generation as segregation of genes begins to occur in second generation. In order to maintain higher yield, hybrid seeds have to be developed every year. It is costly. Hybrid seeds are, therefore, quite expensive to the farmers. Therefore, agriculture scientists are searching for the methods to maintain hybrid traits indefinitely. One of the possible methods is the development of seeds through apomixis. Since the embryo in apomictic seeds often develops from diploid cells, segregation of traits will not occur and the new seeds will contain all the traits of the hybrid variety, Apomixis is controlled genetically. Genes controlling apomixis are being searched. As soon as they are located, efforts will be made to transfer them into hybrid varieties.

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