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Justification for qualification based on EPPO PM 4 Standards
Justification for disqualification
Additional or non-conclusive information
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NAME OF THE ORGANISM: Apscaviroid pustulapyri (pear blister canker viroid) (PBCVD0)

GENERAL INFORMATION ON THE PEST

Name as submitted in the project specification (if different):

Pear blister canker viroid

Pest category:

Viruses and viroids

1- Identity of the pest/Level of taxonomic listing:

Is the organism clearly a single taxonomic entity and can it be adequately distinguished from other entities of the same rank?

Yes

Is the pest defined at the species level or lower?:

Yes

Can listing of the pest at a taxonomic level higher than species be supported by scientific reasons or can species be identified within the taxonomic rank which are the (main) pests of concern?

Not relevant: Fruits (including hops) sector

If necessary, please list the species:

Is it justified that the pest is listed at a taxonomic rank below species level?

Not relevant

Conclusion:

Candidate: Fruits (including hops) sector

Justification (if necessary):

2 – Status in the EU:

Is this pest already a quarantine pest for the whole EU?

Presence in the EU:

Yes

List of countries (EPPO Global Database):

Conclusion:

Candidate

Justification (if necessary):

HOST PLANT N°1: Pyrus (1PYUG) for the Fruits (including hops) sector.

Origin of the listing:

Commission Implementing Directive (EU) 2014/98/EU and Commission Implementing Regulation (EU) 2019/2072

Plants for planting:

Plants intended for planting

3 - Is the pest already listed in a PM4 standard on the concerned host plant?

Yes

Conclusion:

Evaluation continues

Justification (if necessary):

Testing for 'Pear blister canker viroid' recommended in EPPO Standard PM 4-27 Pathogen-tested material of Malus, Pyrus and Cydonia, for Pyrus and Cydonia. However, when responding to the questionnaire, AT and PL supported deregulation. AT questioned economic impact, and PL questioned the main pathway. Evaluation continues for these two criteria.

4 - Are the listed plants for planting the main* pathway for the "pest/host/intended use" combination? (*: significant compared to others):

Yes

Conclusion:

Candidate

Justification:

Pear blister canker viroid has a restricted host range. In addition to the initial natural hosts pear (Pyrus communis) and quince (Cydonia oblonga), PBCVd has been reported in wild pear (Pyrus amygdaliformis) (Kyrakopoulou e al., 2001) and in nashi (Pyrus serotina) (Joyce et al., 2006); the experimental host range is broader, including several species of the genera Chaenomeles, Cydonia and Sorbus, five species of Malus, fifteen spp. of Pyrus and 16 commercial pear cultivars were susceptible to PBCVd, although non expressed symptoms (Desvignes et al., 1999).
PBCVd is unlikely to be seed-transmissible because no symptoms were observed over four year on the indicator A20 propagated onto 200 pear seedlings obtained from a source originally infected with PBCVd.
PBCVd can be transmitted by grafting and budding, and mechanically by slashing pea stems with a razor blade dipped in purified RNA preparations of PBCVd or the viroid inoculum can be rub-inoculated on carborundum dusted cucumber leaves (Flores et al., 2011).
Under field conditions, symptoms induced by PBCVd in the pear indicator cv A20 are restricted to bark pustules appearing 2 years after inoculation and evolving with time to bark scaling or bark splitting and ultimately to tree death (Flores et al., 2011).
The Fruit SEWG considered that plants for planting was a significant pathway.

5 - Economic impact:

Are there documented reports of any economic impact on the host?

Yes

Justification:

The distribution and pathogenic relevance of PBCVd have been most likely underestimated because the majority of pear cultivars are tolerant and because sensitive infected trees decline quickly and show bark cankers and if they were infected by bacteria or fungi, which may be erroneously regarded as the causal agent. PBCVd has been widespread in France and other part of Europe for a long time as indicated by its detection in ca. 10% of 152 old French cultivars (Desvignes et al., 1999, Flores et al., 2011).
Commercial pear cultivars such as Willaims, Comice, Conference, Delbias and Beurré Hardy can be infected but do not develop the typical bark symptoms, as the viroid induces on the pear indicator A20 (Desvignes et al., 1999).
In Australia PBCVd was detected in pear (Pyrus sp.), nashi (Pyrus serotina) and quince (Cydonia oblonga) after testing, none of these trees showed characteristic symptoms (Joyce et al., 2006).

What is the likely economic impact of the pest irrespective of its infestation source in the absence of phytosanitary measures? (= official measures)

Minor

Is the economic impact due to the presence of the pest on the named host plant for planting, acceptable to the propagation and end user sectors concerned?

Yes

Is there unacceptable economic impact caused to other hosts (or the same host with a different intended use) produced at the same place of production due to the transfer of the pest from the named host plant for planting?

Conclusion:

Not candidate

Justification:

In the case of sensitive varieties, the pest may may cause economic damage, but most of the commercially grown varieties in Europe do not show any symptoms, nor negative impact on production. Traded CAC material should remain substantially free from this pest.

6 - Are there feasible and effective measures available to prevent the presence of the pest on the plants for planting at an incidence above a certain threshold (including zero) to avoid an unacceptable economic impact as regards the relevant host plants?

Conclusion:

Justification:

PBCVd is difficult to eliminate through various methods of thermotherapy and/or meristem tip culture (Flores et al., 2011).
Viroid-free propagation material
Decontamination of tools

7- Is the quality of the data sufficient to recommend the pest to be listed as a RNQP?

Conclusion:

Justification:

CONCLUSION ON THE STATUS:

Disqualified: economic impact is considered as acceptable for most commercial varieties.

8 - Tolerance level:

Is there a need to change the Tolerance level:

Yes

Proposed Tolerance levels:

Delisting

9 - Risk management measures:

Is there a need to change the Risk management measure:

Yes

Proposed Risk management measure:

Delisting

REFERENCES:

Devignes JC, Cornaggia D, Grasseau N, Ambrós & Flores (1999) Pear blister caner viroid: host range and improved bioassay with two new pear indicators, Fieud 37 and Fieud 110. Plant Disease 83, 417-422.
Flores R, Ambrós, S. Llácer G & Hernández C (2003) Pear blister canker viroid (Chapter 21). In Viroids (eds Hadidi A, Flores R, Randles JW & Semancik JS). CSIRO Publishing Australia. 153-155
Flores R, Ambrós S, Llácer G & Hernández (2011) Pear blister canker viroid (Chapter 13). In Virus and Virus-Like Diseases of Pome and Stone Fruits (eds Hadidi A, Barba M, Candresse T & Jelkmann W). American Phytopathological Society, St Paul, MN, USA. 63-66.
Joyce PA, Constable FE, Crosslin J, Eastwell K, Howell WE & Rodoni BC (2006) Characterisation of pear blister canker viroid isolates from Australian pome fruit orchards. Australian Plant Pathology 35, 465-471.
Kyriakopoulou PE, Giunchedi L & Hadidi A (2001) Peach latent mosaic and pome fruit viroids in naturally infected cultivated pear Pyrus communis and wild pear P. amygdaliformis: Implication on possible origin of the viroids in the Mediterranean region. Journal of Plant Pathology 83, 369-375.