Mixed infection of a potyvirus and cucumber mosaic virus on Ocimum gratissimum in Okoyong and Boje, Cross River State, Nigeria

Abstract: Viruses have been known to cause considerable yield losses in Ocimum gratissimum (L.), a leafy vegetable commonly known as African basil but locally referred to as “scent leaf’. The crop is cherished for its essential oil, medicinal and agricultural benefits. Virus-like symptoms on leaves causing mosaic, yellowing, leaf malformation and stunting on O. gratissimum (L.) were observed in several farms during the 2018/19 crop season in two locations of Boje and Okoyong in Cross river state. Serological and molecular methods were used to detect viruses infecting the crop at the two locations. Preliminary studies showed the virus could be transmitted mechanically, affirming it was a viral infection. Symptomatic leaf samples from both locations tested positive in antigen-coated plate enzyme-linked immunosorbent assay (ACP-ELISA) to antibodies of genus-specific Cucumber mosaic virus (CMV) and Potyvirus. Primers specific to the coat protein of CMV and the cylindrical inclusion (CI) protein of potyvirus were used for detection of the viruses in reverse transcriptase-polymerase chain reaction (RT-PCR). Obtained sequences were compared to corresponding sequences in the GenBank using the BLASTn program, and the ocimum isolates showed nucleotide sequence similarities of between 89.20 -97.98 % to ocimum potyvirus (MT396942) from Calabar in both locations and two of the collected samples from Okoyong showed a sequence similarity of 100 % with Ocimum CMV isolate from India MN481937. This is the first evidence of potyvirus infection in both locations and mixed infection of CMV and potyvirus on O. gratissimum in Nigeria.