Host range, purification, and genetic variability in Sweet potato chlorotic fleck virus

Sweet potato chlorotic fleck virus (SPCFV) has recently been classified as a putative new member of the genus Carlavirus (family Flexiviridae) on the basis of its molecular properties. In this study, SPCFV was characterized in terms of host range, physical and biological characteristics, and genetic variability. In addition to sweet potato, SPCFV infected some plant species in the families Convolvulaceae, Chenopodiaceae, and Solanaceae. Limited numbers of virus particles were observed in the assimilation parenchyma cells of infected plant tissues; some cells had a distorted and enlarged endoplasmic reticulum though without any cytoplasmic and amorphous inclusions. The normal length of SPCFV particles was determined to be approximately 800 nm. In enzyme-linked immunosorbent assays, polyclonal antibodies raised against purified SPCFV virions were able to detect the virus in infected sweet potato and indicator plant tissues. In immunoelectron microscopy, SPCFV particles were all strongly decorated when reacted with homologous antiserum. Comparison of the 3′ terminal part of the genome of a range of geographically diverse isolates revealed a high level of genetic diversity. The amino acid sequence identity in the coat protein and the nucleic acid binding protein ranged from 89 to 99.7% and from 75.9 to 99.2%, respectively. Phylogenetic analysis of both proteins showed a geographically associated clustering into two genogroups

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