Principles of Plant Breeding (2+1)

Types of apomixis

1. Recurrent Apomixis:
An embryo sac develops from the megaspore mother cell where meiosis is disturbed or from some adjoining cell. Consequently, the egg-cell is diploid. The embryo subsequently develops directly from the diploid egg-cell without fertilization. E.g:Crepis,Taraxacum, Poa(blue grass), and Allium (onion) without the stimulus of pollination. Malus(apple), and Rudbeckiawhere pollination appears to be necessary, either to stimulate embryo development or to produce a viable endosperm.

2. Non -recurrent Apomixis:
An embryo arises directly from normal egg-cell (n) without fertilization. Since an egg-cell is haploid, the resulting embryo will also be haploid.

3. Adventive Embryony:
Embryos arise from a cell or a group of cells either in the nucellus or in the integuments, e.g. in oranges and roses. Since it takes place outside the embryo sac, it is not grouped with recurrent apomixis, though this is regenerated with the accuracy. Embryo within the embryo sac may also develop simultaneously, thus giving rise to poly-embryony condition, as in Citrus, Opuntia.

4. Vegetative apomixis:
In Poabulbosaand Allium, Agave and grass species,vegetative buds or bulbils, instead of flowers are produced in the inflorescence. They can be reproduced without difficulty.