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RMD-09-01: Rubus stunt phytoplasma (RSP), the cause of Rubus stunt disease

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Date issued: 2012-01-16


As described by the International Plant Protection Convention (IPPC), Pest Risk Analysis (PRA) includes three stages: initiation, pest risk assessment and pest risk management. Initiating the PRA process involves identifying pests and pathways of concern and defining the PRA area. Pest risk assessment provides the scientific basis for the overall management of risk. Pest risk management is the process of identifying and evaluating potential mitigation measures which may be applied to reduce the identified pest risk to acceptable levels and selecting appropriate measures.

This Risk Management Document (RMD) includes a summary of the findings of a pest risk assessment and records the pest risk management process for the identified issue. It is consistent with the principles, terminology and guidelines provided in the IPPC standards for pest risk analysis.

Table of Contents

Executive Summary

This Risk Management Document (RMD) is part of a risk analysis process which examines the phytosanitary risk associated with Rubus stunt phytoplasma (RSP). This RMD includes a summary of the findings of a pest risk assessment and identifies and evaluates potential mitigation measures which may be applied to reduce the identified pest risk to acceptable levels. It presents and examines alternative risk management approaches and the risk management approach that was recommended by the Canadian Food Inspection Agency (CFIA) and supported by Canadian stakeholders through consultation.

The Plant Health Risk Assessment Unit of the Plant Health Science Division, CFIA prepared PRA 2000-40: Rubus Stunt Phytoplasma at the request of the Plant Health and Biosecurity Directorate (PHBD), CFIA. The purpose of the PRA is to support the development of specific import policies to prevent the entry of this phytoplasma into Canada. The complete assessment provides specific information pertinent to this phytoplasma along with the characterization and estimation of risks associated with each potential pathway for the organism.

Any Rubus species plant propagative material (excluding seed) can host RSP. Thus, such host material is a potential pathway for introducing RSP into Canada if infested host material is imported into Canada from countries where RSP occurs.

In Canada the organism may survive wherever suitable hosts are grown. The main insect vector of RSP in Europe is the leafhopper, Macropsis fuscula Zett. This vector-species occurs in western North America, including western Canada, where it is found on wild blackberry, especially on Himalaya Blackberry, R. procerus J.P. Müll.

According to Van der Meer (1987), RSP may pose great economic impacts as crop losses can be severe in places where the disease becomes epidemic. Visible symptoms of RSP infection are typically the same in all species and cultivars of Rubus. Common symptoms include, the production of numerous, small, thin, and erect canes at the base of the plant, extensive lateral branching of the whole plant (i.e., bunches of 5-10 fruiting laterals arising from single buds - also referred to as witches'-broom), the over-production of flowers, and phyllody. Many infested cultivated raspberry plants die during the shock stage of infection because they are overgrown by healthier plants. Raspberries grown from cutting of infected plants and planted at a proper distance from each other seldom die and may show some regeneration. However, among the great number of shoots formed, some become larger than the others and bear normal, but smaller berries, which are difficult to harvest. Effective risk mitigations could include the use of a hot-water treatment on Rubus cuttings, which appears to be effective in eliminating the pathogen from host material.

Overall, the CFIA considers RSP to meet the definition of a quarantine pest for Canada. It is rated to have an overall MEDIUM pest risk, based on the PHRA Unit's Model for conducting pest risk assessments.

1.0 Purpose

The purpose of this document is to record a risk management decision and to inform stakeholders of the risk management decision made by the CFIA in regards to the regulatory status of RSP in Canada.

2.0 Scope

This risk management document examines the phytosanitary risks associated with the potential entry of RSP into Canada and summarizes the CFIA decision regarding the regulatory status of RSP in Canada.

3.0 Definitions

Definitions for terms used in this document can be found in the Plant Health Glossary of Terms or the IPPC Glossary of Phytosanitary Terms.

4.0 Background

RSP affects only Rubus spp. (raspberry, blackberry, loganberry, etc.), causing these plants to produce numerous stunted shoots. The United States (U.S.) regulates the importation of Rubus propagative plant material (excluding seed) for this pest. The U.S. quarantine restrictions currently extend to Canada as Canada has not designated RSP as a quarantine pest. RSP has the potential to impact the Canadian Rubus industry by significantly reducing yields and by impacting directly on Canada's export potential for propagative materials, in addition to the present U.S. market access concerns.

5.0 Pest Risk Assessment

The information in this section is taken from PRA 2000-40: Rubus Stunt Phytoplasma. The risk assessment summarises the available information on RSP and evaluates the probability of entry, establishment and spread in Canada, and the potential economic and environmental consequences. Overall risk and uncertainty is summarised in terms of probability and consequences.

5.1 Pest Identity

Name: Rubus stunt phytoplasma

Synonyms: Rubus stunt mycoplasma-like-organism (MLO)

Common names: Rubus stunt disease; Witches'-broom; Heksenbezen, dwergziekte; Rubus Stauche; Verzwergungskrankheit (Van der Meer, 1987).

5.2 Pest Biology

RSP is a very severe disease that naturally affects only plants in the genus Rubus; no immune Rubus germ plasms have been reported (Converse, 1991). Natural infection has been found in all principal European cultivars of raspberries and in many species of wild blackberries (Van der Meer, 1987). Murant and Roberts (1971) indicate that the most important outbreaks in southern England occur in loganberry and blackberry.

RSP is naturally transmitted between plants via leafhoppers of the genus Macropsis and can also be graft transmitted. The major leafhopper vector in Europe is M. fuscula. This leafhopper is also well established in western Canada and in the U.S. on wild blackberry. RSP has not been reported to be seed borne.

Typical symptoms of infection include the production of numerous small, thin canes, extensive lateral branching (also referred to as witches' broom), proliferation of flowers and growth reduction. Fruit produced may be more numerous but smaller and difficult to harvest. Infected plants often die within two years; possibly because they are outgrown by healthier plants.

Infected plants usually do not show symptoms until one year after infection. Some infected plants may never show typical disease symptoms.

5.3 Distribution

RSP has not been found in Canada or in other parts of North America. It occurs in wild and cultivated Rubus in Europe, the Russian Federation and the Middle East.

5.4 Likelihood of Introduction

Entry potential €" Rubus spp. plants, cuttings and canes are the pathway that present a high risk for introduction of RSP. Once infected material (plant, cuttings, etc.) is introduced and cultivated, the phytoplasma is likely to spread locally, within and between adjacent fields.

Currently, Canada limits Rubus germplasm imports from Europe to low numbers of plants that have been solely produced in certification programs where the parental stock has been indexed free from RSP. Thus, the risk of RSP introduction into Canada from European sources has been low. This pest only infects Rubus species and is not transmitted by seed. The risk of introduction via other pathways such as non-host plants or insect vectors is considered negligible.

5.5 Extent of Potential Distribution

Based on the known distribution, which includes Denmark and the United Kingdom, RSP could potentially become established wherever suitable hosts and vectors are found. In Canada, Rubus species, including cultivated and many wild species are found in all provinces. Commercial production of raspberry is primarily carried out in British Columbia, Ontario and Quebec. The major leafhopper vector in Europe, Macropsis fuscula, is present in British Columbia (and is also known to be present in the western U.S.).

5.6 Impacts

  1. Economic - RSP can cause severe economic crop losses when the disease becomes epidemic. Many diseased plants die or may produce some crop but the berries are smaller and difficult to harvest. Plants that are already affected by other diseases are more sensitive to RSP and often die within a year of infection.
  2. Sociological - The establishment of RSP in wild Rubus species in Canada could have significant sociological implications on Canadians for whom wild Rubus species are culturally important.
  3. Environmental - Wild Rubus species grow in all provinces. The longevity of these wild Rubus species would probably be affected in locations where a leafhopper vector is present. The main insect vector in Europe, Macropsis fuscula, is present in British Columbia. The establishment of this disease in the natural environment could affect the fauna which depend on wild Rubus species.
  4. Conclusion - The evidence examined in this pest risk assessment demonstrates that there is a high risk of RSP being introduced into Canada with an overall medium risk rating. The virus is likely to lead to lower overall yields and quality losses to growers, plus possibly eventually leading to plant death. After consideration of all the factors, the CFIA concludes RSP is a quarantine pest for Canada and believes that specific phytosanitary measures are needed to mitigate the risks associated with this pest.

6.0 Pest Risk Management Decision

The following two options were presented for stakeholder consultation, which was completed on July 24th, 2009. The stakeholders consulted included provincial governments, national and provincial industry groups and individuals. Stakeholders who provided comments offered strong support for option B.

A. Maintain the Status Quo

Continue with no regulatory action for RSP. Taking no regulatory action increases the risk of introducing RSP to Canada. In addition, taking no regulatory action may pose a continued barrier to the export of Rubus propagative material to the U.S. due to concerns that RSP could enter Canada via other countries.

The goal of this option would be to allow individual growers to manage this pest risk on their own. This option would not facilitate market access for Canadian Rubus species material.

B. Regulation of Rubus stunt phytoplasma

Regulate RSP by implementing import requirements for the import of vegetative Rubus plant material (excluding seed). Revise existing Permits to Import and all new requests for the import of Rubus species to include the requirement for a Phytosanitary Certificate with an additional declaration certifying the plant material was produced under a National Plant Protection Organization (NPPO) approved certification scheme and found free of RSP based upon visual examination and indexing of parental stock.

Various countries in Europe have certification schemes in place for pathogen testing of Rubus. Therefore, CFIA's introduction of regulation for RSP is expected to have little impact on importers access to Rubus plant material from Europe, other than a possible increase in cost which would be warranted by the potential risk reduction. Importers should be able to readily obtain a Phytosanitary Certificate with an additional declaration as described previously. Requirement for production in a certification scheme will also address control of a number of quality pests of Rubus

The U.S. currently requires that Rubus plants from Canada be certified as having been grown under a CFIA approved certification program. Regulating RSP as a quarantine pest to Canada may provide an opportunity to engage with the U.S. to discuss their import requirements for Rubus plant material originating for Canada.

The goal of this option is to mitigate the risk of this disease entering or establishing in Canada. This option would facilitate market access by demonstrating that Canada is taking action to mitigate the risk of this pest being introduced into Canada.

7.0 Regulatory Decision

Based on scientific information and stakeholder support, the CFIA has decided to add RSP to Canada's regulated pest list and to develop an import policy directive that specifies the import requirements for hosts of this pest.

8.0 References

Garland, J.A., S.J. Miller & A.E. Stahevitch. 1995. PPD Request 95-34c Rubus Plants & Cuttings from Europe. Plant Health Risk Assessment Unit, Canadian Food Inspection Agency, Ottawa.

MacLatchy, I. 2001. PHPD 00-40 Plant Health Risk Assessment Rubus Stunt Phytoplasma. Plant Health Risk Assessment Unit, Canadian Food Inspection Agency, Ottawa.

Rubus Stunt Phytoplasma Pest Fact Sheet. 2001. Plant Health Risk Assessment Unit, Canadian Food Inspection Agency, Ottawa

9.0 Endorsement

Approved by:

Chief Plant Health Officer