Banana bunchy top virus (BBTV) is a plant pathogenic virus of the family Nanoviridae known for infecting banana plants and other crops. It is aphid transmitted.
Definition
Banana bunchy top is a viral disease caused by a single-stranded DNA virus called the banana bunchy top virus (BBTV). It was first identified in Fiji in 1879, and has spread around the world since then. Like many viruses, BBTV was named after the symptoms seen, where the infected plants are stunted and have "bunchy" leaves at the top. The disease is transmitted from plant-to-plant in tropical regions of the world by aphids, banana aphids which can also feed on Heliconia and flowering ginger (from the family Zingiberaceae), which is an important factor in control of the disease. There are no resistant varieties, so controlling the spread by vectors and plant materials are the only management methods. Symptoms include spotting any deformed plant appearance.
Transmission
All babuviruses are aphid transmitted including BBTV. Information is lacking regarding vector-virus interactions.
Host and symptoms
Banana bunchy top disease affects the banana fruit and foliage, and is caused by a single-strand DNA virus, the banana bunchy top virus. BBTV can infect species of the family Musaceae, which includes bananas, plantains, abaca, and more. The aphids also feed on Heliconia and flowering ginger, which are grown in the same regions as bananas and must be considered in management of the disease. It is best to establish a banana production area where these alternate hosts are not present. Any age plants can be infected by this virus, but some varieties of banana, including the Cavendish, are more susceptible to the virus. In areas where the virus is less common, the disease is usually spread by planting diseased suckers at the beginning of the season, which means the season is started with a diseased crop.
The pathogen causes cytopathological effects in the phloem tissue, which is the damaging of the host cells caused by the virus. The damage causes many effects that help to diagnose and characterize the disease. The name of the disease comes from the symptom which occurs in older plants, in which the new leaves that are produced are narrower than normal, yellow, and flat, which causes a “bunchy” appearance at the top of the tree. If any fruit is produced, which is unusual, it will be deformed. In addition, one of the most distinctive symptoms is “Morse code streaking” where the infected cells die and are lighter in color, causing irregular spots and dashes on the leaves that are easier to see when the waxy coating over the petiole is rubbed away.
Distribution
BBTV is a widespread disease in the tropics, and is present in Southeast Asia, the Philippines, Taiwan, Oceania including most of the South Pacific islands and Hawaii, Pakistan (first found 1988, first identified 1991 or 1992), East Asia, parts of India, and is invading Africa . It is especially problematic in East Asia, Oceania, and Hawaii. It was first observed in Hawaii in 1989, and is now widespread on Oahu, in the Kona area, and on Kauai. The disease is currently not present in Central or South America. The pathogen is not present everywhere bananas are grown, but is present in most areas where the vector is also present. These aphids are most likely native to Southeast Asia, but they are present in most areas in the tropics, and almost everywhere bananas are grown. BBTV is spread to new areas by poor agricultural practices, and can be transmitted on plant material from the family Musaceae, the virus' host.
Disease cycle
BBTV is the sole member of the genus Babuvirus in the family Nanoviridae. The genome of BBTV is made up of at least six circular, single-stranded DNA components, each about 1 kilo-base pair in length. Replication takes place by rolling circle replication, a unidirectional nucleic acid replication that can result in rapid synthesis of single-strands of DNA. There are specific virus-like particles that have been proposed as the virions of BBTV but there are still discrepancies in the scientific world about the exact relationship between these virions and the single-stranded DNA virus. Nevertheless, it was demonstrated that the associated ssDNA molecules are transmitted with the disease and therefore are designated as the pathogen.