Nucellar embryony

Nucellar embryony (notated Nu+) is a form of seed reproduction that occurs in certain plant species, including many citrus varieties.

Different from nucellar embryony, double fertilization occurs via the syngamy of sperm and egg cells, producing a triploid endosperm and a diploid zygotic embryo.

The polyembryonic seed is then formed by the many adventitious embryos within the ovule[3] (to picture this process, refer to Figure 1).

The nucellar embryos produced via apomixis inherit its mother's genetics, making them desirable for citrus propagation, research, and breeding.

[3] But, it has been found that nucellar embryo development, under fertilized or unfertilized conditions, can take place in different positions.

[6] An important component of nucellar embryo development is its changing cell wall thickness.

Under conditions where cross-pollination is not present, the ‘Afourer’ mandarin produces a seedless fruit by undergoing parthenocarpy.

Where cross-pollination is present, gibberellic acid is applied and produces a decreased seeding fruit.

Figure 1. depicts the process of nucellar embryony. A) begins with megaspore formation. B) shows the nucellus and forming of cells, nucellar embryonic initial cells, from the nucellus tissue. These initial cells form, divide, and expand. C) The nucellar embryos are developed. If and when a zygote is present, the nucellar embryos supersede the zygote. D) The presence of extra embryos formed from the nucellar tissue gives rise to polyembryonic seeds. E) Polyembryonic seeds germinate and develop. [ 1 ]
Most commercial citrus varieties produce mainly nucellar seedlings.