Polyembryony is the phenomenon of the
formation of more than one embryo in a seed. This phenomenon was first reported
by Leeuwenhock in 1719 in the orange seed.
Following
are the causes of polyembryony in plants –
1. Cleavage polyembryony:- Instead of
developing into a single embryo from zygote, many embryos are developed due to
the cleavage of the zygote or embryo. This type is found in Lotus and many
Orchids.
2. Origin of embryos from synergids and
antipodals:- Apart from the egg, synergids and antipodal cells may develop
into embryos. Example – Prickly poppy, Indian birth wort, Strawberry, etc.
3. Origin of embryos from endosperm:-
In some cases the embryos may develop from endosperm. This type is found in Balanophora.
4. Origin of embryos from cells outside the
embryo sac:- Sometimes embryo may develop from the nucellus and
integuments. This is common in Mango, Lemon, Clove, etc.
5. Formation of more than one embryo sac from
the ovule:- Due to the development of more than one functional megaspore in
an ovule, many embryo sacs may develop which results in the formation of many
embryos. Example – Loranthus.
IMPORTANCE OF
POLYEMBRYONY
Polyembryony
plays an important role in plant breeding and horticulture.
1.
The nucellar seedlings of orange and lemon which are developed from the
nucellar adventive polyembryony have been proved to be better clones of orchard
stock than cuttings.
2.
Nucellar embryos are free from disease.
3.
The lost of vigour due to continued cuttings may be rejuvenated by the
production of nucellar seedlings.
4.
The adventive polyembryony is much useful in the propagation of many fruit
trees.
5.
The adventive embryos may provide genetically uniform seedlings in fruit trees.
6.
It is also useful in the development of homozygous diploids, which are of much
value.
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