Detection of Potato mop-top virus in Potato Tubers and Sprouts: Combinations of RNA2 and RNA3 Variants and Incidence of Symptomless Infections

v2009okpka pk

Strains and distribution of Potato mop-top virus in Finland and other countries of the Baltic Sea region

The spraing symptoms caused by Potato mop-top virus (PMTV, genus Pomovirus) in potato tubers are an important quality problem in potato production in the Nordic countries. PMTV is very difficult to control because the virus remains infective in the resting spores of its vector, Spongospora subterranea (the powdery scab pathogen), in soil for many years and because PMTV-resistant cultivars are not available. Further problems are caused by the year-to-year variability in the portion of infected tubers which develop symptoms, and the similar symptoms caused by the nematode-transmitted Tobacco rattle virus. Hence, detection of PMTV in tubers cannot be based on observation of symptoms only. Since 2005, a coordinated action by the ten Baltic Sea region countries has aimed to determine the current geographic distribution of PMTV, improve diagnostic tools for detection of PMTV, and build up the necessary knowledge base for enhanced control of PMTV and the spraing disease. Because little was known about the genetic variability of PMTV in Finland, other Nordic countries and the few additional countries where PMTV occurs, sequences of PMTV isolates were characterized from 18 spraing-affected tubers grown in the field in Finland and from five symptomless tubers produced in a greenhouse in Latvia. The sequences were compared to ten PMTV isolates of which sequences were available from databases. The variability of the coat protein (CP) gene (98-100 %) and the readthrough (RT) region (97-100 %) in RNA2 was low. In contrast, the 8K gene located at the 3 - proximal part of RNA3 was highly variable, followed by a 3 -untranslated region (3 UTR) that was virtually identical in all isolates compared. Identity of the deduced 8K amino acid sequences was 88-100 % and sequence comparisons indicated existence of two readily distinguishable genetic strains. These results provided the first sequence information on PMTV isolates in Finland and Latvia, and the first report of occurrence of PMTV in Latvia, and the existence of two genetic strains of PMTV. Similar studies on the local PMTV isolates are on-going in Sweden and Norway. The data will be utilized in development of diagnostic tools, resistance breeding, and studies on interactions of PMTV with potato plants and the vector.vokMyynti MTT Tietopalvelut 31600 Jokioine

Sequence variability, recombination analysis, and specific detection of the W strain of Plum pox virus

Plum pox virus (PPV), a member of the genus Potyvirus, is the causal agent of Sharka, the most detrimental disease of stone-fruit trees worldwide. PPV isolates are grouped into seven distinct strains. The minor PPV-W strain was established recently for the divergent W3174 isolate found in Canada. Here, the partial or complete genomic sequences of four PPV-W isolates from Latvia have been determined. The completely sequenced isolates LV-141pl and LV-145bt share 93.1 and 92.1% nucleotide identity, respectively, with isolate W3174, with two regions of higher (>20%) divergence in the P1/HC-Pro and NIa (VPg) regions. Further analyses demonstrated that these two regions correspond to two independent recombination events in the W3174 genome, one involving PPV-M (approximate genome positions 692 to 1424) and the other PPV-D (nucleotides 5672 to 5789). The LV-141pl and LV-145bt isolates appear to be representatives of the “ancestral” PPV-W strain, not affected by recombination. The PPV-W intrastrain variability is substantially higher than that of all other PPV strains, with potential implications for the serological detection of PPV-W isolates. A PPV-W-specific primer pair has been developed, allowing the specific reverse-transcription polymerase chain reaction detection of all five presently available W isolates. The characterization of these new PPV-W isolates sheds light on PPV-W evolutionary history, further supports the hypothesis of its East-European origin, and opens the way for the biological and epidemiological characterization of this poorly known PPV strain