| Legend |
|---|
| Justification for qualification based on EPPO PM 4 Standards |
| Justification for disqualification |
| Additional or non-conclusive information |
| Standard text |
NAME OF THE ORGANISM: Diaporthe strumella (DIAPST)
GENERAL INFORMATION ON THE PEST
Name as submitted in the project specification (if different):
Diaporthe strumella (Phomopsis ribicola)
Pest category:
Fungi
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?
No
Presence in the EU:
Yes
List of countries (EPPO Global Database):
-
Conclusion:
Candidate
Justification (if necessary):
The pest is reported from the Netherlands (1904, 1995), Poland (2008), Denmark (1957), Sweden (1992): occasional findings from mycologists because of typical fruiting bodies (Arnolds et al., 1995; Eriksson, 1992; Mulenko et al., 2008; Munk, 1957; Oudemans, 1904).
HOST PLANT N°1: Ribes (1RIBG) 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?
No
Conclusion:
Evaluation continues
Justification (if necessary):
Not mentioned in PM4/9(2) (2008). Remark: Diaporthe strumella was already reported in 1904 in the Netherlands (Oudemans, 1904). It has also been reported from other European countries (see above). When the PM 4/9 Standard was revised in 2008, this pest was not added.
4 - Are the listed plants for planting the main* pathway for the "pest/host/intended use" combination? (*: significant compared to others):
?
Conclusion:
Candidate by default
Justification:
In 2013 Scarce and Lane, reported on Diaporthe/Phomopsis dieback in blackcurrant. Information on the disease cycle of Diaporthe strumella is limited and the epidemiology of this fungus causing blackcurrant dieback is still not well understood.
The fungus has been detected occasionally on stool bed* plants grown for the supply of hardwood cuttings. This could be a potential source for long-distance spread (Scarce & Lane, 2013).
Diaporthe strumella/Phomopsis ribicola also produces sexual and asexual spores. Both types of spore are most likely to be spread between plants by water splash, but there may also be potential for airborne spread or dispersal by insects. Examination of affected plants and subsequent inoculation testing, has shown that infection via bark wounds is possible (Scarce & Lane, 2013).
Infection of damaged stems occurred following inoculation with either mycelia or spores. No symptoms were found on any unwounded stems, this suggested that damage to blackcurrant stems was required for infection by P. ribicola to occur. This fitted with observation that blackcurrant varieties which were less prone to damage, particularly during the harvesting of blackcurrants were also less prone to stem dieback caused by P. ribicola (Jennings, 2014).
Information is lacking to conclude whether plants for planting is a significant pathway compared to other pathways under (traditional) outdoor conditions. However, the Fruit SEWG reported that Ribes is sometimes produced inside glasshouses (to increase temperature and rooting) on beds with pest-free substrate. This could make plants for planting a significant pathway; however in such conditions, production takes 9 months instead of 1 year, and no particular impact has been observed.
*stool bed is a nursery bed of woody plants propagated by layering.
The fungus has been detected occasionally on stool bed* plants grown for the supply of hardwood cuttings. This could be a potential source for long-distance spread (Scarce & Lane, 2013).
Diaporthe strumella/Phomopsis ribicola also produces sexual and asexual spores. Both types of spore are most likely to be spread between plants by water splash, but there may also be potential for airborne spread or dispersal by insects. Examination of affected plants and subsequent inoculation testing, has shown that infection via bark wounds is possible (Scarce & Lane, 2013).
Infection of damaged stems occurred following inoculation with either mycelia or spores. No symptoms were found on any unwounded stems, this suggested that damage to blackcurrant stems was required for infection by P. ribicola to occur. This fitted with observation that blackcurrant varieties which were less prone to damage, particularly during the harvesting of blackcurrants were also less prone to stem dieback caused by P. ribicola (Jennings, 2014).
Information is lacking to conclude whether plants for planting is a significant pathway compared to other pathways under (traditional) outdoor conditions. However, the Fruit SEWG reported that Ribes is sometimes produced inside glasshouses (to increase temperature and rooting) on beds with pest-free substrate. This could make plants for planting a significant pathway; however in such conditions, production takes 9 months instead of 1 year, and no particular impact has been observed.
*stool bed is a nursery bed of woody plants propagated by layering.
5 - Economic impact:
Are there documented reports of any economic impact on the host?
Yes
Justification:
Branch dieback became a more significant problem in the UK, particularly on certain blackcurrant varieties. The severity of the problem and its speed of spread varied widely between plantations, but in the worst cases up to 80% of plants became affected, with very serious yield loss. The problem has resulted in the premature grubbing of some plantations (Scarce & Lane, 2013).
What is the likely economic impact of the pest irrespective of its infestation source in the absence of phytosanitary measures? (= official measures)
Minor to Medium
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?
No
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?
No
Conclusion:
Candidate
Justification:
In the worst cases it is not acceptable for the grower and will lead to premature grubbing of plantations
In the UK, visits to stool beds during project SF142 revealed low levels of D. strumella at the majority of the stool-bed sites. In some cases the stool-bed stems from which the fungus was recovered showed internal symptoms of wood and pith decay identical to those found in the affected plantation, but in others the fungus was found on stems that had appeared healthy at the time of sampling (Jennings, 2014). Tests are not readily available and it is unclear whether it can prove absence of the pathogen.
Reports – although significant – are rare: the disease has been reported from the UK, but not recently, and there are no reports of blackcurrant cane dieback from other countries (search CAB abstracts, 19/Mar/2024). In responses to the questionnaire, AT questioned whether other species of Diaporthe are also involved. The Fruit SEWG considered that in the situation from the UK, only D. strumella was involved.
In the UK, visits to stool beds during project SF142 revealed low levels of D. strumella at the majority of the stool-bed sites. In some cases the stool-bed stems from which the fungus was recovered showed internal symptoms of wood and pith decay identical to those found in the affected plantation, but in others the fungus was found on stems that had appeared healthy at the time of sampling (Jennings, 2014). Tests are not readily available and it is unclear whether it can prove absence of the pathogen.
Reports – although significant – are rare: the disease has been reported from the UK, but not recently, and there are no reports of blackcurrant cane dieback from other countries (search CAB abstracts, 19/Mar/2024). In responses to the questionnaire, AT questioned whether other species of Diaporthe are also involved. The Fruit SEWG considered that in the situation from the UK, only D. strumella was involved.
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?
Yes
Conclusion:
Candidate
Justification:
According to Scarce & Lane (2013):
Removal of branches affected by dieback, coupled with clearing up and disposal of all dead branch material at the bases of the plants. This should reduce the likelihood of producing fruiting bodies and spores of both the Phomopsis and Diaporthe states of the fungus.
Avoidance, where possible, of physical damage during cultural operations. This can reduce the number of wound sites through which D. strumella may be able to infect branches.
Provide the best possible growing conditions, so that plants do not come under stress. Avoid planting the varieties most prone to attack (Ben Avon, Ben Dorain and Ben Tirran) on all but the most suitable sites. For example, avoid sites prone to drought, waterlogging or desiccating winds.
Some fungicides and also biocontrol agent Serenade might be effective (Jennings, 2014).
Removal of branches affected by dieback, coupled with clearing up and disposal of all dead branch material at the bases of the plants. This should reduce the likelihood of producing fruiting bodies and spores of both the Phomopsis and Diaporthe states of the fungus.
Avoidance, where possible, of physical damage during cultural operations. This can reduce the number of wound sites through which D. strumella may be able to infect branches.
Provide the best possible growing conditions, so that plants do not come under stress. Avoid planting the varieties most prone to attack (Ben Avon, Ben Dorain and Ben Tirran) on all but the most suitable sites. For example, avoid sites prone to drought, waterlogging or desiccating winds.
Some fungicides and also biocontrol agent Serenade might be effective (Jennings, 2014).
7- Is the quality of the data sufficient to recommend the pest to be listed as a RNQP?
No
Conclusion:
Candidate by default
Justification:
Further information is required to determine whether plants for planting is the main pathway and whether economic impact is unacceptable.
CONCLUSION ON THE STATUS:
Recommended for listing as an RNQP, by default (lack of data to determine whether plants for planting is a significant pathway and whether economic impact is unacceptable). Conclusion was that there is insufficient evidence to recommend changes from the current regulation and measures.
8 - Tolerance level:
Is there a need to change the Tolerance level:
No
Proposed Tolerance levels:
9 - Risk management measures:
Is there a need to change the Risk management measure:
No
Proposed Risk management measure:
REFERENCES:
- Arnolds E, Kuyper TW & Noordeloos ME (1995). Overzicht van de paddestoelen in Nederland. 871 pp. NMV, Wijster. (Fungi)
- Eriksson, O.E. 1992. The non-lichenized pyrenomycetes of Sweden. Btjtryck, Lund, Sweden : 208.
- Jennings P (2014). Phomopsis dieback of blackcurrants: methodology development and control. Project for the Agricultural and Horticultural Development Board UK. https://horticulture.ahdb.org.uk/sf-142-phomopsis-dieback-of-blackcurrants-methodology-development-and-control.
- Mulenko, W., Majewski, T., and Ruszkiewicz-Michalska, M. 2008. A preliminary checklist of Micromycetes in Poland. W. Szafer Institute of Botany, Polish Academy of Sciences 9: 752.
- Munk, A. 1957. Danish Pyrenomycetes. A Preliminary Flora.. Dansk Bot. Ark. 17: 1-491.
- Oudemans, C.A.J.A. 1904. Catalogue raisonné des Champignons de Pays-Bas. 558pp. KNAW, Amsterdam.
- Scrace J & Lane C (2013). Blackcurrant dieback. Factsheet 19/3 Project FS 12(223) Soft Fruit. Horticultural Development Company (www.hdc.org.uk), https://projectbluearchive.blob.core.windows.net/media/Default/Horticulture/Publications/Blackcurrant%20dieback