Breeding of Fruit and Plantation Crops

Classification of apomixis

Recurrent apomixis

• The embryo sac (female gametophyte) develops from the megaspore mother cell whether meiosis is disturbed (sporogenesis failed) or from adjoining cell (megaspore mother cell disintegrates).
• The egg cell is diploid and embryo develops directly from the diploid egg cell without fertilization. Generally, somatic apospory, diploid parthernogenesis and diploid apogamy fall under recurrent apomixis.
• Example: Rubus sp. (Raspberry), Malus hupehensis, Malus sikkimensis, Malus sargenti and Malus toringoides (Mitra (1991), Vashishtha et al., (2004))
Non-recurrent apomixis

• The development of embryo takes place from haploid egg cell without fertilization. Such type of apomixis rarely occurs. Generative apospory, haploid parthenogenesis, haploid apogamy and androgamy fall under this category.
Adventive embryony

• This is also known as nucellar embryony or polyembryony. In this case more than one embryo develops in a single seed. In the seed both types of embryo develops i.e. nucellar embryo from nucellar cell and zygotic embryo from egg cell with the result of syngamy.
• Example: Mango cvs. Olour, Goa, Kurukkan, Bappakai, Vellaikolamban, Nileswar Dwarf, Salem, Bellary, Goakasargod, Mazagaon, Chandrakaran etc. (Majumder and Sharma,1991) and most of the species of citrus except Citrus medica (citron), Citrus grandis (Pummelo or Shaddock) and Citrus latifolia (Ghosh, 1991, Vashishtha et al,2004.)
Vegetative apomixis

• This is not common in fruit crops. However, in some cases like Poa bulbosa and some Allium, Agave and grass species vegetative buds or bulbils are produced instead of flower in the inflorescence