Coat protein sequence analysis reveals occurrence of new strains of Sweet potato feathery mottle virus in Uganda and Tanzania

The 3'-proximal part (1.8 kb) of the Sweet potato feathery mottle virus (SPFMV) genome was studied in four SPFMV isolates collected from farmers' fields in western Uganda (SPFMV-Bny), eastern Uganda (SPFMV-Sor) and Bagamoyo district, Tanzania (SPFMV-TZ1 and SPFMV-TZ2). Unlike the other three SPFMV isolates, SPFMV-Sor was not detected with the polyclonal antisera to SPFMV. It showed moderately high coat protein (CP) nucleotide (93.3-96.7%) and amino acid (93.6-96.8%) sequence identity to the isolates of the SPFMV strain group C. In contrast, identities (78.1-80.1%, and 79.9-83.1%) to isolates of the SPFMV strain groups 0, RC, and the East African (EA) strain group were low. Similar to some isolates (SPFMV-CH2 and SPFMV-6) of strain group C, but different from other SPFMV isolates, SPFMV-Sor contained a deletion of 6 nucleotides in the CP-encoding region (CP amino acid positions 62-63). Phylogenetic analysis of the CP sequences indicated that SPFMV-Sor belongs to the SPFMV strain group C that has not been reported from Africa. Sequence data were obtained for the first time from Tanzanian SPFMV isolates in this study, and phylogenetic analysis indicated that they belong to the strain group EA, which is unique to East Africa.