Breeding of Fruit and Plantation Crops

Polyembryony

• The phenomenon in which more embryos are present within a single seed is called polyembryony.
• It may result due to Nucellar embryony e.g., Citrus
• Development of more than one nucleus within the embryo sac (in addition to the egg embryo during the early stages of development) leading to multiple embryos (e.g. conifers).
• Occurrence of polyembryony is widespread in all citrus species but the number of embryos per seed varies from species to species. In rough lemon, it varies from 3 to 5.
• In mango certain cultivars are reported to be polyembryonic with the number of embryos ranging from 2 to 10 and the germination per cent from 40 to 87.
• Polyembryonic seedlings can be identified from its true seedlings by their uniformity and vigorous growth, while the seedling arising from fertilized embryo will be weak.
• The greater vigor in polyembryonic nucellar seedlings is probably due to the elimination of viruses. In mango polyembryony was determined by single dominant gene (Anon, 1996).
• In citrus, all the species are polyembryonic in nature except C.medica (Citron) and C.grandis (Pumelo) which are monoembryonic.
• Though nucellar embryony in citrus is of great value for producing vigorous, uniform and virus free plants, the phenomenon is an obstacle in hybridization.
• In polyembryonic cultivars, the vigorous growth of nucellar embryos inhibits the growth of the zygotic embryo and causes its degeneration prior to seed maturation. Such abortive embryos can be rescued by tissue culture.