Budding is a form of asexual reproduction in which new organisms are produced. These newer offspring are genetically and morphologically similar to the parent organisms because they are formed from their parents' bodies without the involvement of any gametes. The cytoplasmic perturbation that arises from the basal portion of the parent body is called a bud. This bud develops when the parent body receives nutrition from the surrounding medium. The bud may detach itself or remain attached to the parent body. This mode of reproduction can be found in a few unicellular organisms like specific bacteria, yeast and protozoans; several metazoans like cnidarians, hydra, certain fungi, etc
Yeast is a non-green, unicellular microorganism belonging to kingdom fungi. Saccharomyces cerevisiae, also known as brewing yeast or baking fungi, reproduces by developing small outgrowths, i.e. buds from their vegetative body. Such buds receive one daughter nucleus as a result of a division of the parent nucleus. The result of such a division is a large mother cell and a small daughter cell. The buds at times remain attached to the parent yeast cell for a long time, resulting in forming a chain of buds called pseudomycelium. Eventually, the buds are cut off from the parent cell and mature to form new individuals.
When the hydra is healthy, and the food availability is high during the summer months, the hydra reproduces via asexual budding. Near the middle or in the basal part of the body, a bulging (extension) appears due to repeated multiplication of interstitial epidermal cells. This develops as a bud, and the wall contains epidermis and gastrodermis, and the internal lumen also develops along with the parent hydra's gastrovascular cavity. The bud slightly grows bigger, develops a mouth. The tentacles also develop at the free end. When full-grown, the bud constricts at the base and eventually separates from the body of the parent hydra. It feeds and grows into an adult Hydra. At times several buds develop simultaneously on a single parent. In due course of the process, these buds may develop their secondary buds. In such a scenario, a group is formed that temporarily resembles a colonial hydroid.
Asexual reproduction in poriferans is accomplished by budding. An outgrowth from the sponge cylinder arises near its base or attached end to form a bud. An osculum is broken off at Porifera's free end. Fully grown buds at times remain attached with the parent, or it may detach itself to become free and form a new sponge. A new sponge can be formed when the new bud of the Porifera attaches to a new substratum. By this method, numbers of sponges are formed in the colony, or new colonies are formed.
Organisms like Toxoplasma gondii favours core budding or endodyogeny, a method of asexual reproduction adopted by parasites. It is an unusual method in which two daughter cells are created inside a mother cell, consumed by the offspring before their splitting. Although budding is commonly seen in bacteria and fungi, certain flatworms also reproduce by budding. These flatworms are parasitic and adopt budding as the most common mode of reproduction which ensures their certainty of existence in harsh conditions. Sea anemones and jellyfishes also adopt budding in certain phases/stages of their life cycle. The polyp form of jellyfish reproduces by budding, whereas medusa bears gonads which contain gametes.
Budding has a great significance in virology as well. It plays an important role in viral peeling. It is a method by which wrapped viruses acquire their external envelope from the host cell membrane. Arena-, filo-, falvi-, rhabdo-, hepadna-, herpes- and some paramyxoviruses recruit host ESCRT proteins for budding while orthomyxo-, toga and corona are ESCRT independent for budding. In plant reproduction, budding refers to grafting the bud of one plant onto another. Ornamental plants, e.g. hibiscus, rose, holly; nuts, e.g. almond, horse chestnut; fruit plants like peach, cherry, citrus, kiwi and trees like maple, redbud, ginkgo and birch adopts T-budding and chip budding to produce stronger and disease-resistant varieties.
Binary fission is a method of reproduction in many single-celled organisms. In this process, a cell grows and divides into two halves; each half grows rapidly into a new organism. Whereas in budding, the daughter cell arises as a protuberance from the parent cell. In binary fission, both the daughter cells are equal in size and morphology, but the daughter cells are smaller than the parent organism in budding. In binary fission, the existence of the parent cell is lost after reproduction, but the parent exists after detachment of bud in case of budding.