Draft Import Risk Analysis - Biosecurity New Zealand

(Hansen et al. 1974). The presence of the virus in these weed species, which can be found
growing in and around some orchards, suggests that CRLV may have originated in wild hosts
such as balsamroot, and that it is spread from these reservoir hosts into orchards by nematodes.
The accepted host list for CRLV includes Malus domestica (apple), Prunus avium (sweet
cherry), Prunus cerasus (sour cherry), Prunus mahaleb (mahaleb cherry), Prunus persica
(peach), Rubus idaeus (raspberry), Balsamorhiza sagittata, Plantago major (broad-leaved
plantain), Taraxacum spp. (dandelion) (CPC 2007) and Solanum tuberosum (potato) (Thompson
et al. 2004).
Geographical distribution
CRLV was first found in 1935 in Colorado, USA (Bodine and Newton 1942). The virus is
native to western North America where it occurs over a wide geographic area, although typically
primary outbreaks are usually limited to only one or a few trees. The virus occurs primarily in
the foothills west of the Rocky Mountains from Colorado, Utah and California, and north to
southern British Columbia (Stace-Smith and Hansen 1976b). As other viruses can sometimes
induce leaf enation symptoms similar to those of CRLV (Nyland 1976), older reports of CRLV
occurring in areas outside western North America may be questionable.
CRLV is listed as being present in Canada, but few occurrences recorded (CABI/EPPO 2001;
EPPO 2006). There are no reports of the virus occurring in commercial apple orchards in
Canada. In the USA it is listed as having a restricted distribution (CABI/EPPO 2001; EPPO
2006). CRLV has been reported from California, Colorado, Idaho, Montana, Nebraska, New
Mexico, Oregon, Utah, Washington and Wisconsin (CMI 1969; Stace-Smith & Hansen 1976b;
APS-APHIS 1999). Due to the cryptic nature of many apple diseases, it is likely that CRLV is
present in many other regions and countries and as such any country freedom declarations should
be treated with caution.
5.3.1.4. Hazard identification conclusion
The accepted absence of CRLV in New Zealand, the ability of this virus to be vectored by Malus
nursery stock, and its ability to cause disease symptoms on commercial plants in New Zealand
all suggest that CRLV should be considered a potential hazard requiring further assessment.
5.3.2. Risk assessment
5.3.2.1. Entry assessment
In areas where CRLV has an established population, outbreaks appear limited to a few trees
only. The low prevalence of this virus within infected populations suggests that the likelihood of
association with trees from which any Malus budwood is taken for export to New Zealand is
low. As with any virus, the likelihood of survival of long-distance transport in infected
propagation material is high as long as the propagated material remains viable.
It is therefore considered that the likelihood of entry of CRLV into New Zealand with Malus
nursery stock is low and therefore non-negligible.
5.3.2.2. Assessment of exposure and establishment
While hosts of CRLV are available in New Zealand as they are in USA and Canada, the limited
persistence of CRLV in Canadian commercial apple orchards suggests that there may be some
climate constraints on the successful colonisation and spread either of the virus or its vectoring
organism(s). Should this virus be associated with imported Malus nursery stock it would be
expected to use the infested material as a vehicle to allow exposure and establishment in the
New Zealand environment.
DRAFT Import Risk Analysis: Viruses, Viroids, Phytoplasma, Bacteria and Diseases of
Unknown Aetiology on Malus Nursery Stock
August 2009 Page 37 of 203