Plantain and banana (Musa spp.) are among the most important staple crops for food and income generation for the rural and urban populations in the humid forest agroecological zone of West Africa. Until recently, Cucumber mosaic virus (genus Cucumovirus) and Banana streak virus (genus Badnavirus) were the only viruses reported to occur in Musa spp. in West Africa. In 2011, an outbreak of banana bunchy top disease (BBTD) caused by Banana bunchy top virus (BBTV; genus Babuvirus, family Nanoviridae) was reported in Ouémé Département (6°30′N and 2°36′E) in the Republic of Benin (2). BBTV is one of the most economically important pathogens of Musa spp. It is well established in Central Africa and also in Angola, Malawi, and Zambia in Southern Africa (2). Plants infected at early growth stages are severely dwarfed and do not bear fruit. BBTV is transmitted by the banana aphid Pentalonia nigronervosa, which is widespread in Africa (1). The regions in the Republic of Benin affected by BBTV border Ogun State (7°00′N and 3°35′E) of Nigeria. Epidemiological investigations were conducted during May 2012 at 31 locations in Ogun State to determine the potential risk of BBTV spreading into Nigeria. Plants with typical symptoms of BBTD (stunting, narrow and shortened leaves, chlorotic streaks on petioles and pseudostem) were observed in four locations: Ilashe, Odan-Itoro, Ido-Ologun, and Igbogila. Total DNA was extracted from 90 leaf samples randomly collected from symptomatic and asymptomatic banana and plantain plants in these areas. Samples were tested for BBTV by polymerase chain reaction (PCR) using primer pairs, mREP-F and mREP-R, which amplifies a 241-bp of BBTV DNA-mRep segment (1), and Scp-F and Scp-R specific for approximately 1075-bp BBTV DNA-S that encodes coat protein gene (1). The amplicons of expected size were obtained from 17 of 90 samples analyzed (18.8%). BBTV in the symptomatic plants was further confirmed by nucleic acid spot hybridization (NASH) assay using DIG-labeled 1,075-bp probe corresponding to coat protein gene and chromogenic detection as per the previously described protocol (3). The DIG-probe specifically reacted with nucleic acid from the symptomatic plants, but not with negative controls, providing conclusive evidence for the BBTV. The PCR products of DNA-mRep segment amplified from three banana plants infected with BBTV collected in Ilashe (Ipokia Local Government Area) were purified and sequenced in both directions. The sequences of these isolates were 100% identical with each other (GenBank Accession Nos. JX290301, JX290302, and JX290303). A BLASTn search revealed 100% nucleotide sequence identity with a BBTV isolate from Benin (JQ437548) and 99 to 100% identity with DNA-mRep sequences of several other BBTV isolates from Africa, Australia, India, and the South Pacific. Further analysis of the 241-bp mRep gene sequences with Neighbor-Joining phylogenetic analysis grouped the BBTV isolate with the South Pacific isolates. To our knowledge, this is the first report of BBTV in Nigeria. This underscores need for surveys to assess the extent of BBTV spread in Nigeria and strict implementation of phytosanitary measures, including restrictions on the movement of planting material from disease-affected regions, to prevent further spread of this important disease. References: (1) P. L. Kumar et al. Virus Res. 159:171, 2011. (2) B. Lokossou et al. New Dis. Rep. 25:13, 2012. (3) W. S. Xie and J. S. Hu. Phytopathol. 85:339, 1995.

Cotton leafroll dwarf virus (CLRDV) was first reported in the United States (US) in 2017 from cotton plants in Alabama (AL) and has become widespread in cotton-growing states of the southern US. To investigate the genomic variability among CLRDV isolates in the US, complete genomes of the virus were obtained from infected cotton plants displaying mild to severe symptoms from AL, Florida, and Texas. Eight CLRDV genomes were determined, ranging in size from 5865 to 5867 bp, and shared highest nucleotide identity with other CLRDV isolates in the US, at 95.9–98.7%. Open reading frame (ORF) 0, encoding the P0 silencing suppressor, was the most variable gene, sharing 88.5–99.6% and 81.2–89.3% amino acid similarity with CLRDV isolates reported in cotton growing states in the US and in Argentina and Brazil in South America, respectively. Based on Bayesian analysis, the complete CLRDV genomes from cotton in the US formed a monophyletic group comprising three relatively divergent sister clades, whereas CLRDV genotypes from South America clustered as closely related sister-groups, separate from US isolates, patterns reminiscent of phylogeographical structuring. The CLRDV isolates exhibited a complex pattern of recombination, with most breakpoints evident in ORFs 2 and 3, and ORF5. Despite extensive nucleotide diversity among all available CLRDV genomes, purifying selection (dN/dS < 1) was implicated as the primary selective force acting on viral protein evolution.

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