Nucellar embryony

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Most commercial citrus varieties produce mainly nucellar seedlings.

Nucellar embryony (notated Nu+) is a form of seed reproduction that occurs in certain plant species, including many citrus varieties. During the germination of seeds from plants that possess this genetic trait, the nucellar tissue which surrounds the embryo sac can produce additional embryos (polyembryony) which are genetically identical to the parent plant. These nucellar seedlings are essentially clones of the parent. (As opposed to zygotic seedlings, which are sexually produced and inherit genetic material from both parents.)

Nucellar embryony is important to the citrus industry, as it allows for the production of uniform rootstock which yields consistent results in fruit production. However, this trait can interfere with progress in cross-breeding; most commercial scion varieties produce mainly nucellar seedlings which do not inherit any of the traits of the "father" plant.