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Browsing by discipline "Kasvintuotantotieteet (kasvipatologia / kasvivirologia)"

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  • Kashif, Muhammad (2012)
    Sweetpotato is a subsistence crop for many thousands of families across the globe. The present studies in the thesis provide basic knowledge about Sweet potato chlorotic stunt virus (SPCSV) and Sweet potato feathery mottle virus (SPFMV) that were detected and characterized from sweetpotatoes in Guatemala and Honduras. Sweetpotato plants from Central American countries were showing typical virus-like symptoms. Different strategies were adopted for virus detection. SPCSV and SPFMV were found to be infecting sweetpotato plants. SPFMV was detected only in sweetpotato plants from Honduras. SPFMV infection was detected serologically and results were confirmed by RT-PCR and sequencing. A recently developed detection method, based on restrictotypes of PCR products by two different endonucleases, revealed co-infection of SPFMV strains C and RC in a sweetpotato plant from Honduras which was corroborated by sequencing 3'-proximal end (1.8 kb) of the genome and the coat protein (CP) ~940 nt based phylogenetic analysis. SPCSV was detected by double-stranded RNA extraction, confirmed by RT-PCR and subsequent sequencing of the partial HSP70h gene of genomic RNA2 gene of SPCSV. Phylogenetic analysis was done by constructing neighbour-joining tree of aligned nucleotide sequences, including SPCSV-EA isolates and SPCSV-WA isolates from database that clearly differentiated SPCSV isolates of Central American countries. These isolates from Guatemala and Honduras were grouped together with SPCSV-WA isolates from Argentina, United States, Spain, Israel, Nigeria and Egypt. Additionally, the RNase3 gene with UTR at 3´ end of genomic RNA1 gene of SPCSV was sequenced (1264 nt) and aligned against other WA isolates. It was found that the gene for the silencing suppressor protein p22 (676nt) was missing, reflecting intraspecific variation in the genomic structure of SPCSV. These findings revealed the two most important sweetpotato viruses in Guatemala, Honduras, and Central America for the first time and urge further studies of sweetpotato viruses in the region.
  • Chiunga, Evangelista (2013)
    Potato leaf roll virus (PLRV), Potato virus Y (PVY), Potato virus X (PVX), Potato virus S (PVS), Potato virus A (PVA), and Potato virus M (PVM) are widely distributed in potato (Solanum tuberosum) all over the world. This study was conducted to establish if these viruses also infect potato in Mbeya region, Tanzania. A total of 219 potato leaf samples from 13 farmers’ fields were collected. Of these, 20 samples were pressed on FTA cards. Samples were screened for viruses by Double Antibody Sandwich Enzyme Linked Immunosorbent Assay (DAS-ELISA). Those which were pressed on FTA cards were further analysed by Reverse Transcription Polymerase Chain Reaction (RT-PCR). Virus-like symptoms such as yellowish-green mosaic, leaf rolling and vein necrosis were observed and recorded at the time of field sample collection. DAS-ELISA results suggested the occurrence of all six viruses in samples from Mbeya region. RT-PCR analysis confirmed the presence of these viruses except PVY. PVS and PLRV were the most prevalent viruses. Complete coat proteins (CP) encoding sequence of five viruses (PLRV, PVX, PVA, PVS and PVM) were sequenced. Blast searches detected presence of sequences in the GenBank sharing nucleotide sequence identities of 94%-100% with isolates of viruses sequenced in this study. The complete CP sequences of the aforementioned viruses from the current study were closely related with virus isolates from different countries. The Tanzania isolates of PLRV, PVX, PVA, PVS and PVM were each suggested to belong to the one group as well as one isolate. These results are important in seed potato multiplication systems in Tanzania for improving seed quality in the local seed potato chain, an important service currently lacking to potato farmers in Tanzania.