Breeding of Vegetable, Spice and Tuber crops (2+1)

Apomixis

• Apomixis refers to the development of seed without sexual fusion (fertilization). In apomixes, the embryo develops without fertilization.Thus apomixis is alsoan asexual means of reproduction. Apomixis is found in many crop species. Reproduction in some species occurs only by apomixis.This apomixis is termed as obligate apomixes e.g. mangosteen.But in some species sexual reproduction also occurs in addition to apomixis. Such apomixis is known as facultative apomixis.

There are four types of apomixis: viz.

• Parthenogenesis,
• Apogamy
• Apospory and
• Adventive embryony

Parthenogenesis

• Parthenogenesis refers to development of embryo from the egg cell without fertilization.eg. mangosteen

Apogamy

• The origin of embryo from either synergids or antipodal cells of the embryosac is called as apogamy.

Apospory

• In apospory, first diploid cell of ovule lying outside the embryosac develops into another embryosac without reduction. The embryo then develops directly from the diploid egg cell without fertilization.

Adventitious embryony

• The development of embryo directly from the diploid cells of ovule lying outside the embryosac belonging to either nucellus or integuments is referred to as adventitious embryony.e.g. Citrus.