New Disease Reports
New Disease Reports (2007) 15, 5.
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Occurrence in Tunisia of potato tuber necrotic ringspot disease (PTNRD) caused by variant PVYNTN of Potato virus Y

S. Boukhris Bouhachem 1, N. Khamassy 1, L. Glais 2 and C. Kerlan 2*

*camille.kerlan@rennes.inra.fr

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Accepted: 16 Feb 2007

Potato tuber necrotic ringspot disease (PTNRD) (Beczner et al., 1984) is now found worldwide. The causal agent has been characterised as a variant of Potato virus Y (PVY), designated PVYNTN. Most PVYNTN isolates display a recombinant genome with exchanges of sequences in the HC-Pro, NIa and CP genes between PVYN and PVYO (Glais et al., 2002; Nie & Singh, 2003).

In 2005, PTNRD symptoms were observed in autumn crops in Southern Tunisia. Many harvested tubers displayed superficial necrotic ring spots. Plantlets grown from a collection of these tubers tested positive for PVY when tested by ELISA using an anti-PVY antiserum (Inra-Fnpppt, Le Rheu, France). Eleven isolates were aphid transmitted from potato plantlets onto Nicotiana tabacum cv Xanthi. Isolates from tobacco were compared to well-characterized isolates representative of PVY strains and variants: PVYN, PVYNTN, PVYNW and PVYO (Glais et al., 2002). All isolates were maintained in a regulated (20°C ± 2°C), insect-proof greenhouse.

All Tunisian isolates tested in tobacco gave leaf distortion and vein necrosis, as did reference isolates of the three PVYN subgroups. Tunisian isolates also reacted positively in ELISA with specific anti-PVYN antibodies (Inra-Fnpppt, Le Rheu, France) and negatively with anti-PVYO-C antibodies (Adgen, Ayr, UK). Hence biological and serological typing showed that none of the Tunisian isolates belonged to the PVYNW variant since PVYNW isolates are known to induce necrosis on tobacco and to react negatively with anti-PVYN antibodies.

Four Tunisian isolates were characterized at the molecular level using RT-PCR protocols with specific primers, either based on the polymorphism in the P1 gene (Glais et al., 2001), or targeting the three recombination sites specific to PVYNTN isolates, RJ1 and RJ2 (Nie & Singh, 2003), RJ3 (Glais, unpublished). Tunisian isolates gave PCR products with sizes identical to those produced by the reference PVYNTN isolates, which demonstrated they are PVYNTN isolates with recombination events in HC-Pro/P3, CI/NIa and C-ter CP regions.

This is the first report of PVYNTN isolates associated with PTNRD in Tunisia. PTNRD disease has never been previously documented in any potato growing area in Tunisia. Further studies are in progress to assess the incidence of the PVYNTN variant in both spring and autumn potato crops.

Figure1+
Figure 1: Distinct ringspots on the surface of a potato tuber cv Monalisa harvested in Sidi Bouzid. Sunken arches will then become necrotic with some cracks through the periderm.
Figure 1: Distinct ringspots on the surface of a potato tuber cv Monalisa harvested in Sidi Bouzid. Sunken arches will then become necrotic with some cracks through the periderm.
Figure2+
Figure 2: Agarose gel electrophoresis analysis of RT-PCR products amplified using a protocol based on the polymorphism in the P1 gene (Glais et al, unpublished). Lane E: SmartLadder (EuroGentec), lane 1: PVYNTN-H, lane 2: PVYNTNFrOrl, lanes 3-6: Tunisian isolates.
Figure 2: Agarose gel electrophoresis analysis of RT-PCR products amplified using a protocol based on the polymorphism in the P1 gene (Glais et al, unpublished). Lane E: SmartLadder (EuroGentec), lane 1: PVYNTN-H, lane 2: PVYNTNFrOrl, lanes 3-6: Tunisian isolates.
Figure3+
Figure 3: Agarose gel electrophoresis analysis of RT-PCR products amplified using a protocol targeting the three recombination junctions, RJ1 and RJ2 (from Nie & Singh, 2003), RJ3 (from Glais, unpublished). Lanes E and 1-6 as Fig 2.
Figure 3: Agarose gel electrophoresis analysis of RT-PCR products amplified using a protocol targeting the three recombination junctions, RJ1 and RJ2 (from Nie & Singh, 2003), RJ3 (from Glais, unpublished). Lanes E and 1-6 as Fig 2.

Acknowledgements

The authors would like to thank A. Najjar and M. Guillet for their excellent assistance and R. Kutcher for his help with English.

References

  1. Beczner L, Horváth H, Romhányi I, Förster H, 1984. Studies on the etiology of tuber necrotic ringspot disease in potato. Potato Research 27, 339-352.
  2. Glais L, Tribodet M, Kerlan C, 2001. Molecular detection of particular PVY isolates: PVYNTN and PVYNW. Proceedings of the 11th EAPR Virology Section Meeting, Havlíčkův Brod – Třešť (Czech Rep.), 70-71.
  3. Glais L, Tribodet M, Kerlan C, 2002. Genomic variability in Potato potyvirus Y (PVY): evidence that PVYNW and PVYNTN variants are single to multiple recombinants between PVYO and PVYN isolates. Archives of Virology 147, 363-378.
  4. Nie X, Singh RP, 2003. Specific differentiation of recombinant PVYN:O and PVYNTN isolates by multiplex RT-PCR. Journal of Virological Methods 113, 69-77.
This report was formally published in Plant Pathology

©2007 The Authors