Epsilon Archive for Student Projects

Abstract

Potato virus Y (PVY) is the most important and widespread virus infecting potato (Solanum tuberosum) worldwide. Recently, new PVY recombinant genotypes have emerged and their incidence is increasing throughout the world. In Sweden, the non-recombinant PVYO strain used to be most common, but it now seems to have been replaced by the recombinant genotypes, as has been reported for many European countries. This study intends to biologically, serologically and molecularly characterize Swedish PVY isolates from potato. To study the present genetic diversity of PVY in Swedish potato, 50 symptomatic potato samples from different parts of Sweden were selected for characterization of the infecting PVY genotypes using serology, multiplex-PCR, sequence analyses and inoculation tests. In DAS-ELISA, one sample was positive only for serotype O, 31 samples for only serotype N and 15 samples for both serotypes. None of the samples were positive for serotype C. Three samples did not react with any of the employed antibodies, but tested positive in the subsequent PCR analyses. To identify specific PVY genotypes, multiplex-PCR was used with diagnostic patterns for known genotypes. The identities of the amplification products were verified by sequencing. Among 42 Swedish samples analysed by PCR, PVYNTN was the most common genotype with 19 samples having a single infection by PVYNTN and 19 samples having mixed infection by PVYNTN and one or several other PVY genotypes. PCR analyses also indicated frequent infections by PVYN-W and other recombinants, most often in mixed infection with PVYNTN. The previously dominant PVYO strain was detected in 12 of the samples in mixed infections. In inoculation tests, extracts of all 16 tested samples were found to induce vein and stem necrosis on tobacco (Nicotiana tabacum), which is indicative of the N pathotype of PVY, including PVYNTN. Leaf/tuber extracts of 12 samples initially identified to contain the PVYO strain were inoculated into potato cv. Désirée (Nytbr:nc:nz:Ndtbr) and screened for hypersensitive response (HR). Unexpectedly, no HR was observed in cv. Désirée for extract from any of these samples. These findings indicate the absence of PVYO and PVYD strains from the tested samples and that the PVYO patterns obtained in the multiplex-PCR were generated by other related genotypes. Full-genome sequencing is required to be carried out to identify in more detail the exact PVY genotypes in selected samples. It can be concluded that PVYO in Sweden mainly has been replaced by recombinant genotypes, such as PVYNTN and PVYN-W.