Bract mosaic is a viral disease caused by the Banana bract mosaic virus (BBrMV) and transmitted by aphids. Its common name comes from the characteristic mosaic symptoms on the flower bracts. Infection can result in growth defects, reduced suckering and misshapen fruit. Severe incidences can lead to fruit rejection and consequently to economic losses.
Bract mosaic was first noted in the Philippines in 1979. In 1966, a disease with the same symptoms, but unkown etiology, had been reported as Kokkan disease in Kerala, India. The causal agent of Kokkan disease was later confirmed to be BBrMV. The disease has also been reported in Sri Lanka, Vietnam and Western Samoa.
Mosaic patterns on the bracts of the inflorescence are diagnostic. Green or red streaks or spindle-shaped lesions can appear on leaf petioles and sometimes on the midrid of new leaves (not to be confused with nitrogen deficiency). Chlorotic streaks on the leaf blade can also indicate infection. Sometimes the only symptom is on the leaf sheaths. Peeling back the dead outer leaf sheaths will reveal spindle-like streaks on the exposed pseudostem. Chlorotic streaks may also appear on bunch stems.
The virus can be transmitted in a nonpersistent manner (i.e. retained by the vector for a short period) by at least three species of aphid, Pentalonia nigronervosa, Aphis gossypii and Rhopalosiphum maidis. The virus can also be transmitted by infected planting material.