Which one of the following is of great significance in horticulture?

Nucellar adventive polyembryony is of great significance in horticulture. In this process, embryos develop directly from the nucellus or integument cells, which are maternal tissues. As a result, the embryos are genetically identical to the parent plant, ensuring the preservation of desirable traits (clonal propagation). Furthermore, seedlings raised from nucellar embryos are generally free from viruses and exhibit higher vigour compared to those produced through vegetative propagation methods like cuttings. This is extensively utilized in the cultivation of crops like Citrus and Mango.

Answer: Nucellar adventive polyembryony.