2. “APO” (away from) and “MIXIS” (act of mixing or mingling).
Discovered by Leuwenhoek as early as 1719 in Citrus seeds.
Definition
“The process of development of diploid embryos without
fertilization.”
Or
“Apomixis is a form of asexual reproduction that occurs via seeds,
in which embryos develop without fertilization.”
Or
“Apomixis is a type of reproduction in which sexual organs of
related structures take part but seeds are formed without union of
gametes.”
3. Fig-Initiation and progression of Apomitic Mechanisms relative to events in
the sexual life cycle of Angiosperms.
Source-
http://www.plantcell.org/content/plantcell/16/suppl_1/S228/F1.large.jpg?wi
dth=800&height=600&carousel=1
4. In apomictic species, sexual reproduction is either suppressed or
absent.Therefore,based on the occurrence of Sexual reproduction,
Apomixis is of two types:-
Facultative Apomixis
Obligate Apomixis
Types of Apomixis:
Maheshwari (1950) classified apomixis into four groups:
(a)Recurrent Apomixis : Embryo sac develop without meiosis from
diploid cell.
Diplospory : Embryo sac develop from MMC.
Apospory : Embryo sac develop from any vegetative cell of ovule, than
embryo is developed from diploid egg cell.
E.g. Poa, Taraxacum and Allium without the stimulus of pollination
Parthenium, Rubus, Malus (apple) with the stimulus of pollination.
5. (b) Non-Recurrent Apomixis: Embryo develop from any cell of
embryo sac (haploid cell)
Haploid parthenogenesis : Embryo develop from egg cell
Haploid Apogamy(Pseudogamy): Embryo developed from
synergids or antipodal cells.
E.g. Solanum nigrum and Lilium species
(c)Adventitious Embryony or Nucellar Embryony:-
Embryo directly develop from nucellus or integuments(no
production of embryosac). It occurs in many plant species but
is most prominent in tropical and sub-tropical tree species, like
citrus and mango.
(d) Vegetative apomixis or bulbils:
E.g. Allum, Agave, Poa and Diascorea and some grasses
6. PRACTICAL IMPORTANCE:
Rapid production of pure lines (Genetically uniform
individuals)
Heterosis or Hybrid vigour can permanently be fixed in crop
plants , thus no problem for recurring seed production of F1
hybrids.
Adventive embryos are better clones than cuttings.
Embryos formed through apomixis are generally free from
infections.E.g Adventive embryony well known in Citrus, is
being used in the Production of root stock and virus free
section material.
