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
Symptoms:
-
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
Transmission:
-
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
Symptoms:
-
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.
Transmission:
-
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
Symptoms:
-
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
Transmission:
-
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
Symptoms:
-
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.
Transmission:
-
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.