Plant Propagation and Nursery Management (1+1)

Polyembryony

Polyembryony means that more than one embryo develops within a single seed. It is also known as adventitious embryony (Nucellar embryony or Nucellar budding).

• Polyembryony can develop from several distinct causes. Specific cells in the nucellus or sometimes with integument have embryos. Genetically, these embryos have the same genotype as the parental plant and are apomictic.
• Adventitious embryony occurs in many plant species but is most common in citrus and mango. In these species, both zygotic and apomictic embryos are produced. In other species (e.g. Opuntia), no pollination or fertilization is needed.
• Polyembryony is common in mango and citrus. In trifoliate orange (Poincirus trifoliata) several seedlings arise from one seed.
• Of these seedlings, one seedling, usually the weakest may be sexual, and the others arise apomictically from cells in the nucellus, which are diploid copies of the mother plant.
Horticultural significance of polyembryony

Nucellar seedlings in citrus are completely free from viruses, because the embryo sac and adjoining tissues are impregnated at flowering time with some unknown powerful substances which kills all the viruses. For immediate requirement of planting material, development of nucellar lines is the quickest and easiest method. The major possible horticultural applications of polyembryony are:

• Nucellar seedlings are true-to-type seedlings
• Such seedlings are genetically uniform and can be used as virus free
Rootstock

• More vigorous seedlings – continuous vegetative propagation leads to decline in vigour in citrus
• Development of virus free seedlings and bud wood
• Significance in breeding programmes