First Report of Banana bunchy top virus in Banana (Musa spp.) from South Africa

Bananas (Musaceae, Zingiberales) are one of the most important fruit crops and a staple food in many developing tropical and subtropical regions (Kumar et al. 2011). In southern Africa, banana production is threatened by viral diseases including Banana bunchy top virus (BBTV) (family Nanoviridae, genus Babuvirus), cause of the most devastating virus disease of banana. A detection survey for BBTV was done in South Africa in 1996 confirmed the absence of BBTV in the Kiepersol Region of Mpumalanga Province (Pietersen et al. 1996). No other surveys were conducted since then in South Africa. The disease is spread by the banana aphid Pentalonia nigronervosa Coquerel (Hemiptera: Aphididae) and infected propagation material. In June 2015, five ‘Williams’ plants, showing symptoms resembling BBTV, including streaks on the pseudostem and upright bunchy appearance, were submitted for identification to the Virology Diagnostic Lab at Agricultural Research Council-Plant Protection Research (ARC-PPR). The plants originated from a farm close to Hibberdene in the KwaZulu Natal South Coast production region (30°30.636’ S; 30°30.653’ E). A BBTV-specific PCR was done using the protocol published by Thomson and Dietzgen (1995), using primer pairs BBT-1 and BBT-2, amplifying a fragment of the putative replicase gene. The five plants tested positive for BBTV, and the PCR products (∼349 bp) of two of the accessions, 15/1408 and 15/1410, were directly sequenced using Sanger sequencing and 321 bp of both sequences were deposited in GenBank (Accession Nos. KU196167 and KU196168). A noninfected banana plant was included as a control. Phylogenetic analyses of the partial replicase genomic region grouped accessions 15/1408 and 15/1410 with the South Pacific group that included accessions from India, Pakistan, and other regions in Africa with a sequence identity of 99% (Kumar et al. 2011). A second confirmation test used a BBTV-specific enzyme-linked immunosorbent assay (ELISA) supplied by Agdia (catalog no. SRA24700) using the manufacturer’s instructions. The five plants tested positive for BBTV in the ELISA test, confirming the previous positive results. Forty-four additional samples were included in the ELISA test. These samples were collected randomly from 14 blocks on the same farm (30°30.636′ S; 30° 30.653′ E) and included symptomatic and nonsymptomatic plants. BBTV was detected with ELISA in 34 of these plants; 10 tested negative. In one block, all the sampled plants (4) tested negative. In three other blocks, positive and negative plants were recorded. In the remaining 10 blocks, all collected plants tested positive. Intense management strategies, including removal of infected plants and spraying for aphids, were implemented on the farm to prohibit the spread of the virus to neighboring plantations. The ELISA test confirmed the earlier detection of BBTV with PCR and sequencing. This is the first report of BBTV on Musa spp. from South Africa. Strict implementation of phytosanitary measures will be necessary to prevent the spread of this virus to other regions in the country. The need to do extensive surveys for the presence of BBTV in other banana production regions in South Africa is highlighted by this finding.