BANANA BUNCHY TOP DISEASE (Mandeep Poudel)

Banana bunchy top virus (BBTV) is one of the most serious diseases of banana. Once

established, it is extremely difficult to eradicate or manage.

Family: Circoviridae (from being circular, round)

Genus: Nanovirus (from being small, nanos = dwarf)

Symptoms Initially BBTV consist of

dark green streaks in the veins of lower portions of the leaf midrib and the leaf stem (petiole). The streaks also occur, but

are less prominent, in the veins of the leaf blade

(lamina). This symptom is some- times referred to

as “Morse code streaking” because the

streaks are irregular and resemble a series of “dots” and “dashes.”

Symptoms:

The hook-like extensions of the leaf lamina veins can be seen in the narrow,

light-green zone between the midrib and the lamina, hooks point down along the midrib

toward the petiole. They can best be seen

by back-lighting the leaf against the sky.

SymptomsThey appear to be

“bunched” at the top of the plant, the symptom for which

this disease is named.

The new leaves emerge with difficulty, are narrower than

normal, are wavy rather than flat, and have yellow

(chlorotic) leaf margins.leaves are stiff and

erect, are shorter and narrower than normal leaves.

Disease spread and developmentPropagative materials such as rhizomes, suckers, or tissue-cultured meristems and over short distances by the banana aphid Pentalonia nigronervosa.

Banana aphid acquires the virus after at least four (but usually about 18) hours of feeding on an infected plant.

Remains for a period of 15–20 days, i.e. through its adult life.

Nature of Damage:Disease symptoms usually appear about a month after infection.

The aphids are most likely to be hiding or feeding. This includes the leaf petioles and the “pockets” where the petioles separate from the pseudostem.

The inflorescence and fruit bunch either fail to form or fail to emerge from the banana pseudostem.

Severely infected banana plants usually will not fruit, but if fruit is produced, the banana hands and fingers are likely to be distorted and twisted

Control Measures:Minimise virus infection: Quarantine measures, the use of virus-free propagating material, locating new plantations away from older infected ones, and destroying all volunteer banana plants.

Reduction in spread: Roguing of infected andnearby plants seems to reduce the rate of virus spread.

Spraying with Insecticidal soaps.

Attempts to control the aphid vector with insecticideshave little effect on the spread of this virus.