Detection of a New Strain of the Yambean mosaic virus in Senna hirsuta (Irwin and Barneby) in Calabar, Southern Nigeria

Background: Hairy senna is an edible weed grown for both its vegetables and as a hedge plant in farms and backyard gardens in Calabar. Senna hirsuta leaf samples showing virus-like symptoms were collected in the growing seasons of between 2018 and 2020 from backyard gardens and farms in Calabar and the surrounding area. Methods: The virus was isolated and transmitted by mechanical inoculation for host range studies. Seed transmissibility and transmission by aphids were further used for detection. Reverse transcription polymerase chain reaction (RT-PCR) using primers specific to the cylindrical inclusion protein gene (CI) of potyviruses followed by sequencing was used for molecular identification. The neighbour-joining phylogenetic tree was constructed to determine the relationship of the Calabar isolate with those from other parts of the world. Result: For the host range studies, four species belonging to the Fabaceae family were infected by the isolate, indicating a narrow host range. The virus was found to be seed transmissible and could be vectored by both Aphis craccivora and Aphis spiraecola. Obtained DNA fragments with the expected size of~700 bp were amplified and a pairwise comparison with other potyviruses revealed a 94-95.87% similarity with complete sequence of YBMV (JN190431). Phylogenetic analysis placed the senna isolate in the same clade as the Brazilian isolates (MK825543 and MK825544) and JN190431. On the basis of this, the virus is adjudged to be the Nigerian strain of YBMV (JN190431).