India is the largest producer of Banana in the world and accounts for about 21 percent of the world banana produce, producing over 31 million metric tonnes of banana every year. However, banana continues to face pests and disease infestations affecting the production and productivity in India. Viral diseases are a major constraint to production since they affect the yield and quality.
In India, Banana bunchy top virus (Babuvirus), Banana streak virus (Badnavirus), Banana bract mosaic virus (Potyvirus) and Cucumber mosaic virus (Cucumovirus) are the major viral diseases infecting the banana growing regions of the country.
1. Banana bunchy top disease
- Initial symptoms of Banana Bunchy Top Disease consist of appearance of dark green streak in the veins of lower portion of the leaf midrib and leaf stem.
- The symptom of the prominent green streaks in veins of lamina is referred to as ‘Morse code streaking’.
- Plants with advanced stage of infection show rosette appearance with progressively shorter, narrow, brittle textured leaves giving rise to the common name of ‘bunchy top’.
- Infected banana plants usually will not fruit, however if fruit is produced the banana hands and fingers are likely to be distorted and twisted.
- Banana is transmitted by infected suckers and banana aphid.
Fig: Morse code streaking on the leaves
Pcr, ® & Chen, Yan & Hu, Xiaoping. (2013). High-throughput detection of banana bunchy top virus in banana plants and aphids using real-time TaqMan. Journal of virological methods. 193. 177-183. 10.1016/j.jviromet.2013.06.013.
Fig: Bunchy top disease-late stage infection
- Primary mode of transmission is through infected suckers, corms/bits and also through tissue propagated material.
- Secondary transmission is by banana black aphid Pentalonia nigronervosa in a semi persistent manner
2. Banana bract mosaic disease
- Banana bract mosaic disease is characterized by presence of spindle shaped pinkish to reddish streaks on pseudostem, midrib and peduncle.
- Typical mosaic and spindle shaped mild mosaic streaks on bracts, peduncle and fingers are also observed.
- Suckers exhibit unusual reddish brown streaks at emergence and separation of leaf sheath from central axis.
- Clustering of leaves at crown with a travelers palm appearance, elongated peduncle and half filled hands are its characteristic symptom.
- The disease is caused by a virus belonging to potyvirus group. The virions are flexuous filamentous
- The virus is primarily spread through infected suckers.
- The virus might be transmitted through aphid vectors. In the field, aphids vectors such as Aphis goosypii, Pentolonia nigronervosa and Rhopalosiphum maidis transmit the disease.
3. Banana streak disease
- Symptom for streak virus disease can vary from an inconspicuous flecking to lethal necrosis depending on the isolate of the pathogen, the host cultivar and the environment.
- Symptoms mostly include narrow, discontinuous and sometimes continuous chlorotic or yellow streaks that run from the leaf midrib to the margin.
- Spindle or eye-shaped patterns are present in some cases. Yellow blotches have also been associated with banana streak.
- Sometimes the lamina can be distorted. Streaks later darken to orange and often become brown or black.
- Necrosis has also been seen on the midrib and petiole. Necrosis occurs more under low temperature, short-day conditions.
- The intensity of symptoms has been associated with the concentration of virus in the tissue; the higher the virus concentration, the more severe the symptoms.
- Other symptoms associated with disease are stunting, cigar leaf necrosis, internal necrosis of the pseudostem, a reduction in bunch size, incomplete emergence of bunches and bunches emerging through the side of the pseudostem. Occasionally, dark streak symptoms may be visible on the pseudostem and fingers may be distorted
- Banana streak viruses are pararetroviruses belonging to the genus Badnavirus, in the family Caulimoviridae.
- Natural field spread occurs by either mealybugs or use of infected planting material, such as suckers.
- Vegetative transmission is the primary mode of transmission.
Fig: Symptoms of Banana streak virus showing lines of yellow in large blocks from midrib to leaf edge, turning brown or black with age.
4. Cucumber mosaic disease
- Diffused mosaic/ line pattern/ ring spots symptoms appear in affected leaf lamina.
- Deformation and curling of leaves are also reported.
- Some other symptoms include rosette appearance of leaf arrangement and conspicuous inter-veinal chlorosis.
- Symptoms are usually more severe when temperature falls below 24˚C.
- Affected plants are stunted and will throw small bunches with malformed fingers.
- Sometimes plants may die if severe strain of the virus affects the plant.
- The virus is transmitted through infected suckers and it is also acquired from a wide range of host plants growing near banana fields through aphid vectors.
- The most common aphid are: Aphis gossypii and Rhopalosipum maidi.
- The virus is most frequently transmitted mechanically.
Fig: Cucumber Mosaic Virus (CMV) infected Banana plant.
Dheepa, R. and Subramanian Paranjothi. “TRANSMISSION OF CUCUMBER MOSAIC VIRUS (CMV) INFECTING BANANA BY APHID AND MECHANICAL METHODS.” (2010).
With use of quality tissue culture banana planting material it is ensured that virus free and genetically uniform plants are provided to the farmers. Under NCS-TCP, batch certification is done prior to dispatch of plants to check that the plants are virus free.
Suggested References for disease symptoms:
R. Selvarajan and M. M. Mustaffa, Viral Diseases of Banana, Technical Bulletin, NCRB-ICAR.