Detection and Sub-Group Classification of CMV Isolates Infecting Tomato in Southwest Nigeria.

Abstract A total of 92 tomato leaf tissue samples collected from 10 farmers’ fields spread across southwestern Nigeria were indexed by antigen coated plate enzyme-linked immunosorbent assay (ACP-ELISA) for the presence of Cucumber mosaic virus (CMV). In ACP-ELISA, 26.1% of the total samples collected tested positive for CMV with varying percentage incidences across sampled locations. The presence of CMV was confirmed in a subset of samples using RT-PCR followed by direct sequencing of amplified DNA. Sequence analysis of the partial coat protein coding sequence indicate that tomato-infecting CMV isolates from southwest Nigeria shared 91.6-99.4% & 94.9-99.1% nucleotide (nt) and amino acid (aa) identities among themselves and 91.6-98.0% & 94.1-98.3%, 89.4-94.1% & 93.2-98.3% and 75.2-78.8% & 84.0-87.3% with corresponding nt & aa sequences of CMV isolates belonging to subgroups IA, IB and II, respectively. Phylogenetic analysis and estimates of genetic distances, distinguished all the tomato-infecting CMV isolates from southwest Nigeria as members of subgroup I with four isolates clustering into IA and three into IB. To our knowledge, this is the first time CMV has been identified conclusively in tomato plants from Nigeria using RT-PCR and sequencing. Together with previous reports of presence of CMV subgroup IA in yams from the Republic of Benin and IB in cowpea samples from five African countries, results from this study suggests that subgroup I CMV isolates may be endemic across West Africa probably as a consequence of introduction of contaminated propagules and/or horizontal and vertical transmission by resident vectors.