Diversity of banana streak-inducing viruses in Nigeria and Ghana: Twice as many sources detected by immunoelectron microscopy (IEM) than by TAS-ELISA or IC-PCR

Our previous study had shown that some Musa leaf samples with Banana streak symptoms tested negative for Banana streak virus (BSV) in triple antibody-sandwich ELISA (TAS-ELISA). Therefore, in this study 63 additional Musa leaf samples were tested for BSV by TAS-ELISA, immunoelectron microscopy (IEM) and immunocapture polymerase chain reaction (IC-PCR). Sensitivity tests by sap dilution end-point analyses indicated that IC-PCR was considerably more sensitive than IEM for detecting typical BSV, while IEM proved to be of similar sensitivity as TAS-ELISA. However, when leaf samples of Musa plants, obtained from different farmers' fields in Nigeria and Ghana and some Nigerian sources maintained in the greenhouse were screened for BSV, more than twice as many samples revealed BSV-like particles by IEM than were detected by TAS-ELISA or IC-PCR. Of the 51 leaf samples that were BSV positive in all tests taken together, 48 were positive by IEM, 25 by IC-PCR and only 19 by TAS-ELISA. Upon IEM examination, typical bacilliform BSV-like particles were clearly recognized although in very diverse concentrations. Bacilliform particles deviating in length from the main particle populations or showing an angularly bent morphology were found. Occasionally, in certain samples and with certain antisera the IEM decoration tests revealed mixtures of strongly decorated and weakly decorated BSV-like particles or bacilliform particles which did not at all react with the antibodies available. This proved, the occurrence, besides the presence of typical BSV, of diverse populations of BSV-like viruses in West Africa.