First Report of Banana Bunchy Top Virus in Malawi

Banana plants of the Cavendish subgroup (Musa AAA, locally known as "Kabuthu") with classical banana bunchy top virus (BBTV) symptoms were observed to be widespread in Thiwi Valley, Salima Agricultural Development Division, Malawi. The symptoms included marginal yellowing of the younger leaves, dark green, dot-dash streaks along the veins, petioles, and midribs, and shortened internodes. The aphid vector of this virus, Pentalonia nigronervosa, was abundant on bananas in this area (H. Thindwa, personal communication). Young leaf and midrib samples from apparently healthy plants and plants with symptoms were transported to the United Kingdom for testing. In a triple antibody sandwich enzyme-linked immunosorbent assay (ELISA) with poly- and monoclonal antibodies specific for BBTV (1), the samples from symptomatic plants gave positive reactions (OD infected ≥ OD healthy + 3SE healthy). Polymerase chain reaction (PCR) amplification tests were performed for confirmation with oligonucleotide primers BBT1 and BBT2, which are homologous to conserved regions in BBTV DNA component 1. All ELISA-positive samples produced a PCR amplification product of about 349 bp, whereas the healthy control samples did not. The sizes of the DNA fragments produced following restriction enzyme digest of the PCR product suggest that the Malawi virus falls within the South Pacific group of BBTV isolates (2). The presence of both the virus and its vector has the potential for causing great economic damage to this important banana-growing region, and recommendations have been made to eradicate all plants with symptoms. References: (1) R. G. Dietzgen and J. E. Thomas. Australas. Plant Pathol. 20:161, 1991. (2) M. Karan et al. J. Gen. Virol. 75:3541, 1994.