Occurrence of two serotypes of sweet potato chlorotic stunt virus in East Africa and their associated differences in coat protein and HSP70 homologue gene sequences

Abstract

Amongst samples of the sweet potato chlorotic stunt crinivirus (SPCSV) obtained from crops of sweet potato in Uganda, two serotypes (S(EA1) and S(EA2)) were distinguished using a panel of monoclonal antibodies (Mabs) to a Kenyan isolate of SPCSV. S(EA1) serologically resembled the Kenyan isolate of SPCSV whereas S(EA2) has not previously been reported. S(EA1) was predominant in eastern Uganda whereas S(EA2) was predominant in southern and western Uganda. S(EA2) tended to occur in more severely diseased sweet potato plants than S(EA1). RNA was extracted from eight plants and replicate clones representing the heat shock protein 70 (HSP70) homologue and coat protein (CP) genes were generated by reverse transcription and PCR. Sequence analyses revealed substitutions at two nucleotide positions in the HSP70 homologue gene, although neither affected deduced amino-acid sequences. Nucleotide substitutions in the CP gene region, which led to 11 amino-acid substitutions, revealed two major groupings plus other minor variants. The EMBL accession numbers of the sequences reported in this paper are AJ010754 through to AJ01769 (coat protein sequences) and AJ010914 through to AJ010929 (partial HSP70 homologue gene sequences).