The discovery and characterisation of Plum pox virus (PPV) isolates in Montenegro

M. Viršček Marn^1*, I. Mavrič Pleško¹ and J. Zindović²

¹ Agricultural Institute of Slovenia, Hacquetova 17, SLO-1001 Ljubljana. Slovenia
² Biotechnical Institute – Podgorica, Bulevar Svetog Petra Cetinjskog bb, 81 000 Podgorica, Montenegro

*mojcavm@kis.si

Accepted for publication 11/07/07

In 2006 20 extensive and intensive plum orchards, surrounding Nikšić in Montenegro, were screened for the presence of Plum pox virus (PPV) symptoms. Mild to severe symptoms were found in 15 orchards, usually only on some trees.  In total 19 samples were collected and 17 proved to be positive by DAS-ELISA (Bioreba, Switzerland).  Of these positives, 16 were selected for molecular identification.  PPV isolates have been assigned to two major (PPV-D and PPV-M) and two minor groups (PPV-EA, PPV-C).  Recently, a fifth group (PPV-REC) has been established, which corresponds to naturally-occurring recombinants between PPV-M and PPV-D isolates.  All PPV-REC isolates share the same recombination breakpoint on the NIb polymerase gene and therefore conventional CP gene-based molecular and serological methods are not able to discriminate between PPV-M and PPV-REC isolates.  In this report, subgroup characterization was performed using two different PCR systems: one positioned downstream of the recombinant crossover (using the PPV-M and -D specific primer pairs P4/P3-M and P4/P3-D respectively; Dallot et al., in press); and the other upstream of the recombination breakpoint (using the primer pairs CIf/CI-M (PPV-M specific) and CIf/CI-D (PPV-D specific); Glasa et. al., 2002). The results showed the presence of PPV-D type isolates in 4 samples.  These samples were also negative for PPV-M when tested by TAS-ELISA (Agritest, Italy). The remaining 12 samples were PPV-M positive by TAS-ELISA.  Of these, seven proved to be of PPV-REC type by RT-PCR.  However, the isolate type could not be determined for the remaining five samples using the previously described method.  Therefore they were further analyzed using primer pairs mM5/mM3, mD5/mD3 and mD5/mM3 (Šubr et al., 2004), situated around the recombination breakpoint.  All samples gave a positive result only with primer pair mD/mM3 and were therefore also identified as the PPV-REC type.

Figure 1: Plum pox virus (PPV) symptoms on plum leaves from an infected orchard in Montenegro

Although plum production is important in Montenegro, data about PPV infection is scarce.  Sharka symptoms were observed by Mijušković (2002), but until now the presence of PPV was never confirmed.  As a result, this is the first report confirming PPV as being present in Montenegro.

References

Glasa M, Marie-Jeanne V, Labonne G, Subr Z, Kudela O, Quiot JB, 2002. A natural population of recombinant Plum pox virus is viable and competitive under field conditions. European Journal of Plant Pathology 108, 843-853.

Dallot S, Glasa M, Pittnerova S, Paunovic S, Jevremovic D, Kamenova I, Kominek P, Virscek-Marn M, Mavric I, Milusheva S. Prevalence and genetic structure of PPV-M in six European countries. Acta Horticulturae (in press).

Mijušković M, 2002. Prilozi proučavanju biljnih bolesti u Crnoj Gori I. Podgorica, Montenegro: Montenegrin Academy of Sciences and Arts. [In Serbian]

Šubr Z, Pittnerová S, Glasa M, 2004. A simplified RT-PCR-based detection of recombinant Plum pox virus isolates. Acta Virologica 48, 173-176.