Draft Import Risk Analysis - Biosecurity New Zealand

3. Hazard identification
Species of Malus are grown in most countries of the world with Malus domestica having by far
the largest global distribution of all the species. These species have therefore been exposed to
organisms and diseases that are not found in the natural range of this genus. Where Malus
domestica is grown commercially in significant quantities and is supported by a relatively welldeveloped
plant protection industry, an accurate and relatively complete record of the associated
organisms or diseases should be available. For many other countries, however, Malus species
may be widespread but as domestic amenity plants only, having little commercial value and no
or little supporting plant protection industry. Records of associated organisms or diseases in
these countries would be expected to be unreliable and incomplete. Therefore while the scope of
this risk analysis includes Malus nursery stock imported from any country in the world, the
information supporting the development of the hazard organism lists in reality originates from a
relatively small number of commercially significant apple producing countries.
It is the recommendation of this risk analysis that the considerable uncertainty associated with
these secondary countries be considered either in the measures applied in the associated import
health standard or through the countries allowed to export Malus material to New Zealand.
3.1. Potential hazard organisms
Within this risk analysis the only potential hazard organisms under consideration are the viruses,
viroids, phytoplasma, bacteria and diseases of unknown aetiology.
3.1.1. Viruses
The Oxford English Dictionary defines a “virus” as:
“An infectious organism that is usually sub microscopic, can multiply only inside certain
living host cells (in many cases causing disease) and is now understood to be a noncellular
structure lacking any intrinsic metabolism and usually comprising a DNA or
RNA core inside a protein coat”
This includes umbraviruses that have no virion protein genes of their own, and use the virion
proteins of their symbiotic helper viruses instead (Brunt et al. 1996).
A virus is an elementary bio-system that possesses some of the properties of living systems such
as having a genome and being able to adapt to changing environments. However, viruses cannot
capture and store free energy and they are not functionally active outside their host cells
(Fauquet et al. 2005). Virus particles (virions) consist of nucleic acid surrounded by proteins,
the protein coat or capsid. The shape and dimensions of virus particles are characteristic of each
virus. The virus genome consists of either ribonucleic acid (RNA) or deoxyribonucleic acid
(DNA) in either single- or double-stranded form, though most contain single stranded RNA
(Bokx & van der Want 1987). There are no recorded instances of plant viruses causing diseases
in humans.
3.1.2. Viroids
The Oxford English Dictionary defines a “viroid” as:
“An infectious entity similar to a virus but smaller and consisting of a strand of nucleic
acid only, without the protein coat characteristic of a virus”
DRAFT Import Risk Analysis: Viruses, Viroids, Phytoplasma, Bacteria and Diseases of
Unknown Aetiology on Malus Nursery Stock
August 2009 Page 13 of 203