Draft Import Risk Analysis - Biosecurity New Zealand

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Viroids are pathogens that are present in all parts of the plant, both vegetative (roots, shoots, leaves, tubers) and reproductive (flowers, seed). Viroids exist in plants as a protein-free unencapsulated circular RNA molecule. Viroids consist of a covalently closed circular RNA that shows a high degree of base pairing, which results in a thermodynamically stable structure consisting of loops and helices. Viroid RNA does not code for any proteins and depends on the host plant for replication and circularization. Viroids are considered parasites of the transcription machinery of the cell, while viruses are parasites of the translation process (Constable et al. 2006). Viroids can be classified into two families, the Avsunviroidae and the Pospiviroidae, according to their structure. There are a total of five genera in the former and two in the latter family. When sequence similarity between closely related viroid strains is greater than 90%, they are called variants of the one-viroid species. If there is less than 90% similarity, the viroid strain is considered a new and a distinct species (Constable et al. 2006). 3.1.3. Bacteria The Oxford English Dictionary defines a “bacterium” as: “Any of several types of microscopic or ultramicroscopic single-celled organisms very widely distributed in nature, not only in soil, water, and air, but also on or in many parts of the tissues of plants and animals, and forming one of the main biologically interdependent groups of organisms in virtue of the chemical changes which many of them bring about, e.g. all forms of decay and the building up of nitrogen compounds in the soil” Bacteria are prokaryotes and are generally single-celled micro-organisms that have a cell membrane, a rigid cell wall, and often one or more flagella. The cytoplasm contains small (70S) ribosomes and DNA that are not bound within organelles. Bacteria form into a number of shapes and some can transform themselves into or produce spores. Almost all plant-pathogenic bacteria are rod-shaped and range from 0.6 to 3.5 µm in length (Agrios 2005). 3.1.4. Phytoplasma According to the USDA Phytoplasma Resource Centre 4 , “phytoplasma” are: “Very small bacteria that are enveloped only by a single membrane and do not possess a cell wall like typical bacteria” Phytoplasma are also prokaryotes and are single-celled micro-organisms that have a cell membrane but lack a rigid cell wall. From a taxonomic and structural perspective phytoplasma are otherwise as bacteria although without a rigid cell wall they cannot form pre-determined shapes. 3.1.5. Diseases of unknown aetiology “Diseases of unknown aetiology” are diseases or disorders of plants, in this case Malus species, for which science has yet to find a causative organism or group of organisms. It is therefore possible that a disease of unknown aetiology may not in fact be a disease but rather a physiological condition, or may be caused by a known organism attributed to a separate condition. 4 http://www.ba.ars.usda.gov/data/mppl/phytoplasma.html Page 14 of 203 August 2009 DRAFT Import Risk Analysis: Viruses, Viroids, Phytoplasma, Bacteria and Diseases of Unknown Aetiology on Malus Nursery Stock
The descriptions and assessment of the diseases of unknown aetiology rely heavily on the Washington State University National Research Support Project website (WSU (2003) “Virus Free” Stone & Pome Fruit - Pome Fruit Diseases caused by Viruses (NRSP5) 2001). 3.2. Organisms and diseases recorded on Malus The viruses, viroids, phytoplasma, bacteria and diseases of unknown aetiology that have been recorded as being associated with Malus nursery stock are listed in Appendix 1. Table 1 in Appendix 1 provides a list of the scientific and common names of these organisms, their recorded synonyms and the key references sourced to link these potential hazard organisms with the commodity and the their presence (or not) in New Zealand. Table 3.1 provides the answers to a series of questions that culminates in the decision as to the status of these organisms on the Malus nursery stock pathway, either potential hazards or not potential hazards. This table lists a total of 19 viruses, four viroids, three phytoplasma, 34 diseases of unknown aetiology, and five bacteria. Information on the meaning s of the column headings is provided in MAF (2006). Table 3.1: Potential hazards – Status determination Scientific name In NZ? Virus 5 Vector of a Hazard In NZ but association with goods increases hazard In NZ but geographically bounded In NZ but has different host associations DRAFT Import Risk Analysis: Viruses, Viroids, Phytoplasma, Bacteria and Diseases of Unknown Aetiology on Malus Nursery Stock No or little information on organism Under official control or notifiable Potential hazard Apple chlorotic leaf spot virus Yes N/A No No No No No No Apple latent spherical virus No N/A N/A N/A N/A Yes No Yes Apple mosaic virus Yes N/A No No No No No No Apple stem grooving virus Yes N/A No No No No No No Apple stem pitting virus Yes N/A No No No No No No Carnation ringspot virus [strains N, A and R] Yes N/A Yes No Yes No No Yes Cherry rasp leaf virus No N/A N/A N/A N/A No No Yes Clover yellow mosaic virus No N/A N/A N/A N/A Yes No Yes Horseradish latent virus No N/A N/A N/A N/A Yes No Yes Prunus necrotic ringspot virus Yes N/A No No No No No No Sowbane mosaic virus No N/A N/A N/A N/A Yes No Yes Tobacco mosaic virus Yes N/A No No No No No No Tobacco necrosis virus ( Tobacco necrosis virus A, Tobacco necrosis virus D) Yes N/A No No No No No No Tobacco ringspot virus Yes N/A No No No No No No Tomato bushy stunt virus Tomato ringspot virus (Grape yellow vein strain) Tomato ringspot virus (except Grape yellow vein strain) 5 Significant strains are listed separately No N/A N/A N/A N/A Yes No Yes Yes N/A No No No No No No No N/A No No No No No Yes August 2009 Page 15 of 203
Page 1 and 2: Draft Import Risk Analysis: Viruses
Page 3 and 4: Contributors to this risk analysis
Page 5: 8.10. Apple McIntosh depression age
Page 8 and 9: Organism (Name and organism type) A
Page 10 and 11: 1. Project background and process 1
Page 12 and 13: The process outlined in figure 2.1
Page 14 and 15: 2. Commodity and pathway descriptio
Page 16 and 17: Flowering and fruiting are sporadic
Page 18 and 19: MAF (2003) PP42: Inspection and Cle
Page 22 and 23: Scientific name In Vector In NZ but
Page 24 and 25: 4. General phytosanitary measures f
Page 26 and 27: e detected while the specificity le
Page 28 and 29: maintained within the facility. MAF
Page 30 and 31: Postman D pers. com. (2008) Comment
Page 32 and 33: 5.1.2. Risk assessment 5.1.2.1. Ent
Page 34 and 35: Virus indexing of mother plants Whi
Page 36 and 37: Kegler et al. 1983). Dianthoviruses
Page 38 and 39: ecosystems. Naturalised introduced
Page 40 and 41: Koenig R, Rüdel M, Lesemann D E (1
Page 42 and 43: Symptoms by affected plant part inc
Page 44 and 45: The likelihood of exposure and esta
Page 46 and 47: the causal agent as CRLV. It theref
Page 48 and 49: Hansen, A J; Parish, C L (1990) Tra
Page 50 and 51: 5.4. Clover yellow mosaic virus (Cl
Page 52 and 53: Environmental consequences While th
Page 54 and 55: Baker, C A, Beckham, K, Hiebert, E
Page 56 and 57: Pearson M N, Clover G R G, Guy P L,
Page 58 and 59: 5.6.2. References Bancroft JB, Toli
Page 60 and 61: TBSV spreads (principally on plants
Page 62 and 63: Pest free place of production (PFPP
Page 64 and 65: 5.8. Tomato ringspot virus (ToRSV)
Page 66 and 67: MM.106 rootstock, because it moves
Page 68 and 69: ange of host crops overseas that to
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Bioassays are effectively used with
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5.9. Tulare apple mosaic virus (TAM
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5.9.3.2. Option evaluation There ar
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6. Risk analyses - Viroids 6.1. App
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The potential environmental impact
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6.1.4. References Allan H H (1982)
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6.2.2. Risk assessment 6.2.2.1. Ent
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There is currently no information o
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No insect vector is known, but root
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a. Pest free area (PFA) (see sectio
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6.4. Peach latent mosaic viroid (PL
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7. Risk analyses - Phytoplasma 7.1.
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7.1.3. Risk management 7.1.3.1. Ris
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7.2. Candidatus Phytoplasma mali (A
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plum), Pyrus communis (European pea
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7.2.2.5. Risk estimation The likeli
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Larivière, M-C (Ed.) (2005) Checkl
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8. Risk analyses - Diseases of unkn
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impacts, while being significant on
Page 108 and 109:
BA (2002) Review of Post-Entry Quar
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8.2.2.3. Consequence assessment Spr
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8.3.2. Risk assessment 8.3.2.1. Ent
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Mitigation by industry As discussed
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8.4. Apple bunchy top agent 8.4.1.
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8.5. Apple dead spur agent 8.5.1. H
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8.5.2.4. Conclusion of consequence
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8.6. Apple decline agent 8.6.1. Haz
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Human health consequences Apple Dec
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8.7. Apple freckle scurf agent 8.7.
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However, as discussed in section 4.
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8.8. Apple green dimple and ring bl
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8.9. Apple junction necrotic pittin
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they may potential receive from imp
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8.10. Apple McIntosh depression age
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8.10.2.6. Assessment of uncertainty
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8.11. Apple narrow leaf agent 8.11.
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eceive from importing such material
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8.12. Apple necrosis agent 8.12.1.
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8.14. Apple Newton wrinkle agent 8.
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8.15. Apple painted face agent 8.15
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8.16. Apple pustule canker agent 8.
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Xylella fastidiosa. NAPPO (North Am
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The likelihood of exposure and esta
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old fruit bearing trees, woody inde
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period, woody indexing on the Malus
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8.19.2. Risk assessment 8.19.2.1. E
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Indexing of mother plants Given tha
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8.21.1.4. Hazard identification con
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d. Indexing of mother plants either
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8.22. Apple transmissible internal
Page 184 and 185:
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Jones, A L; Aldwinckle, H S (1990)
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9. Risk analyses - Bacteria 9.1. Ps
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symptoms in New Zealand all suggest
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papulans associated with imported M
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Bradbury, J F (1986) Guide to plant
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Glossary of Terms Area An officiall
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Pest Any species, strain or biotype
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Appendix 1 Potential hazards - desc
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Scientific name Common name Synonym
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Page 206 and 207:
Page 208 and 209:
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Pearson M N; Clover G R G; Guy P L;
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