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Occurrence of Banana Bunchy Top Disease Caused by the Banana bunchy top virus on Banana and Plantain (Musa sp.) in Cameroon

Banana bunchy top virus (BBTV; genus Babuvirus, family Nanoviridae) is a serious pathogen of banana (AAA genome) and plantain (AAB genome) (Musa sp.). It is transmitted by the banana aphid (Pentalonia nigronervosa) in a persistent manner (1). In recent years, BBTV has emerged as a major constraint to banana and plantain production in several countries of Africa and had been previously confirmed in viz., Burundi, Central African Republic, Republic of Congo, Democratic Republic of Congo, Egypt, Equatorial Guinea, Gabon, Malawi, and Rwanda (1) and more recently in Mozambique and Zambia (2) and Angola (3). To assess the potential threat of BBTV in West-Central Africa, we conducted surveys in August and September 2008 in 36 major banana- and plantain-producing regions of Littoral, South, Southwest, and Western Provinces of Cameroon. DNA was extracted from 520 plants and tested by PCR with primers specific for a conserved domain of BBTV DNA-R segment (4). A 240-bp DNA fragment specific to the virus was amplified in 31 samples from 18 plantain and 13 banana plants from Southwest, Western, and Southern Cameroon. Among virus-positive samples, symptoms (upright leaf growth, small leaves with pale chlorotic margins that choked the throat of the plant creating the bunchy appearance at the top) typical of bunchy top disease were observed only in banana (cv. Cavendish Williams) from Muea in the Southwest Province. PCR products obtained from the symptomatic and asymptomatic banana (Cavendish Williams) from Muea and Abang, respectively, were cloned into pCR2.1 (Invitrogen, Carlsbad, CA) and two independent clones from each isolate were sequenced in both directions. Pairwise comparison of these sequences showed 100% sequence homology. A comparison of these sequences (Accession No. F580970) with corresponding sequences in GenBank showed 99% nt sequence identity with a BBTV isolate from Angola (Accession No. EU851977) and 96 to 98% identity with BBTV isolates belonging to the South Pacific group (Australia, Africa, South Asia, and South Pacific). However, the BBTV isolate from Cameroon showed 85 to 90% sequence identity with isolates belonging to the Asian group (China, Indonesia, Japan, Taiwan, Philippines, and Vietnam). To further confirm the virus identity, complete nucleotide sequence of the DNA-SCP segment that encodes for the virus coat protein was determined using PCR amplification of viral DNA (1), cloning of products into pCR2.1 vector, and sequencing. The derived sequence (1,075 nt; Accession No. GQ249344) in BLAST search at NCBI database revealed 98% nt sequence identity with coat protein gene of BBTV isolate from Burundi (Accession No. AF148943). These results, together with phylogenetic analysis, indicate that BBTV isolates from Cameroon have greater affinity to the South Pacific group. To our knowledge, this is the first report of BBTV in West-Central Africa. The occurrence of BBTV in the Western and Southern provinces of Cameroon, neighboring north of Gabon, suggests a possible spread of the virus from Gabon. This report also underscores the need to monitor other countries of West Africa for BBTV and enforce quarantine measures to prevent further spread through infected suckers from endemic areas of West and Central Africa.

References: (1) I. Amin et al. Virus Genes 36:191, 2008. (2) W. T. Gondwe et al. InfoMusa 16:38, 2007. (3) P. L. Kumar et al. Plant Pathol. 58:402, 2009. (4) S. Mansoor et al. Mol. Biotechnol. 30:167, 2005.