E. M. Ateka

Biological and molecular variability among geographically diverse isolates of sweet potato virus 2.

Summary.Sweet potato virus 2 (SPV2) is a tentative member of the genus Potyvirus, family Potyviridae. In addition to the type isolate of SPV2 recently characterised in greater detail, twelve additional isolates of this virus were obtained from sweet potato clones originating from China, Portugal, South Africa and Zambia. Sequences of the coat protein (CP) gene and 3′ non-translated region (NTR) were determined. Comparisons of the CP gene sequences of these isolates revealed nucleotide and amino acid sequence identities ranging from 81 to 99% and from 86 to 99%, respectively. Phylogenetic analysis of sequences distinguished several groups, which partially correlated with the geographic origin of the isolates, and indicated that some isolates from South Africa and a Zambian isolate are most distinct both in CP and 3′NTR sequences. Host range studies of a selected number of isolates revealed some differences in test plant reactions, which appeared to correlate to some extent with the geographic origin and molecular distinctness of the SPV2 isolates. The results strongly suggest the occurrence of biologically and genetically diverse strains of SPV2.

Further characterization of 'sweet potato virus 2': a distinct species of the genus Potyvirus.

Summary.An incompletely described potyvirus isolate from sweet potato in Taiwan, referred to as ‘sweet potato virus 2’ (SPV2), was further characterised. Electron microscopy revealed that SPV2 has filamentous particles of 850 nm in length and induces cytoplasmic cylindrical inclusions consisting of pinwheels and scrolls. The virus was mechanically transmitted to several species of the genera Chenopodium, Datura, Nicotiana, and Ipomoea. Two biotypes of Myzus persicae transmitted SPV2 in a non-persistent manner. Decoration titer experiments revealed a distant serological relationship between SPV2 and other potyviruses infecting sweet potato. The 3’-terminal 2006 nucleotides of the viral RNA were determined and shown to be a potyviral genome fragment comprising the coding region for the C-terminal half of the NIb protein, the entire coat protein cistron, and the 3’ untranslated region (UTR). Comparison of the capsid protein and 3’ UTR sequences of SPV2 with those of other potyviruses demonstrated that it is a distinct member of the genus Potyvirus (family Potyviridae). We propose that SPV2 is named Sweet potato virus Y.