An investigation of prevalance and the detection and race identification of South African potato viruses

[摘要] ENGLISH ABSTRACT: Infection of potatoes by viral pathogens causes reduced crop yield and subsequent economic loss. InSouth Africa Potato virus Y (PVY) and Potato leafroll virus (PLRV) are the two most destructive virusesinfecting potatoes. Several other viral pathogens exist, including Potato virus X (PVX), Potato virus M(PVM), Potato virus A (PVA), Potato virus S (PVS), Potato mop-top virus (PMTV), Tomato spotted wiltvirus (TSWV) and Potato spindle tuber viroid (PSTVd). Although the aforementioned pathogens arefound infecting potatoes around the world, there are no published information pertaining to the prevalenceof these viral agents in South Africa. Currently, the occurrence of PLRV infection in potatoes of SouthAfrica has reached epidemic proportions. A previous phylogenetic investigation undertaken in ourlaboratory of South African PLRV isolates, using coat protein (CP) gene sequences, found large variationbetween native South African PLRV isolates and most other isolates from elsewhere in the world; withtheir nearest relatives being single isolates from Australia and North America.In this study the incidence of PVX, PVM, PVA, PVS, PMTV, TSWV and PSTVd was investigated. Alarge number of potato plant and tuber samples was collected and infected samples were identified withreverse transcriptase polymerase chain reaction (RT-PCR) amplification of the CP gene or the wholegenome in the case of PSTVd. The amplified nucleic acid segments were sequenced, aligned withinternational reference sequences and analysed phylogenetically to determine their relative relationshipswith these reference sequences. The CP genes of PLRV isolates were sequenced and phylogeneticallyinvestigated to determine how these new isolates compared relative to the previous findings from ourlaboratory. In addition, the complete genomes of two PLRV isolates were sequenced and phylogeneticallyinvestigated as a preliminary study to investigate the apparent increase of pathogenicity of certain variantsof South African PLRV.Results obtained showed that only PVX and PVS were present in the samples collected and theincidences of these viruses were very low (2.0 and 1.1% respectively). The phylogenetic analyses of theCP genes, indicated that the PVX and PVS variants isolated in this study, were part of the dominant typesof variants found worldwide. From the analyses of the PLRV CP and whole genome sequences, it wasdetermined that many of the PLRV variants found in South Africa, are genetically distinctly differentfrom those around the world. This warrants further investigation into the increased pathogenicityexperienced with South African PLRV.

[发布机构] Stellenbosch University