Further Evidence for Limited Genetic Diversity among East African Isolates of Sweet potato chlorotic stunt virus

In Africa, the crinivirus Sweet potato chlorotic stunt virus (SPCSV) exists in two serologically and genetically distinct strains, geographically distinguished as a West African (SPCSVWA) and an East African (SPCSVEA) strain. To obtain a better understanding of the genetic diversity among SPCSVEA isolates, the major coat protein (CP) and heat shock protein 70 homologue (Hsp70h) gene sequences of 24 further isolates of SPCSVEA were determined and compared. SPCSVEA diversity was also examined using available monoclonal antibodies (mAbs) to SPCSVEA but there was no apparent coincidence between CP and partial Hsp70h gene nucleotide sequences and the subdivision of SPCSVEA isolates by the mAbs into two serotypes, suggesting this latter may not be of great biological significance. The nucleotide (nt) sequences of isolates of SPCSVEA displayed a high degree of conservation and the only variation observed consisted of a few base exchanges. Pairwise alignments of CP nucleotide sequences revealed differences of <4% between SPCSVEA isolates. Comparisons with published SPCSV sequences confirmed a more distant relationship (up to 34.6% nt; 12% amino acid divergence) between the Hsp70h sequences of isolates of SPCSVEA and SPCSVWA and indicated that SPCSVEA in East and Southern Africa is the more homogeneous than SPCSVWA isolates from West Africa, North and South America, which were up to 12.4% nt divergent among themselves.