Wollemia nobilis (Wollemi Pine) - Biosecurity New Zealand

3.4.4 Association of Organisms of Negligible Risk
It is accepted in the scientific community that it is usual for plants to form associations with
micro-organisms that are considered to be endophytes or saprobes (saprophytes). In the case
of endophytes these organisms live symbiotically within the plant tissue and, in return for a
safer environment and perhaps some nutrition, it is believed can in some circumstances
provide limited protection to the plant from other disease-causing organisms. In some studies
endophytes were found to be relatively host specific. Saprophytes live on or around the plant
and survive on dead organic material. In contrast to endophytes, saprophytes are not usually
host specific. While neither type of micro-organism are likely to cause diseases on plants, it
is likely that the majority of disease-causing micro-organisms were at one stage saprophytes
or endophytes as the mechanisms for plant invasion by these disease-causing microorganisms
are modified from those used by endophytes and saprophytes.
From a biosecurity risk-perspective therefore, these endophytic or saprophytic organisms are
very unlikely to have any negative or unwanted impact on the New Zealand economy,
environment or human health. While it is possible that a plant endophyte or saprophyte may
act as a plant pathogen or parasite on an alternative plant host, there is little indication at this
time that an event such as this would happen more than very rarely.
Currently the risk from these organisms is considered negligible, as no phytosanitary
measures are taken to ensure imported nursery stock is free of them. Should the biosecurity
risks from these types of organisms be considered non-negligible, the options for managing
the risks are limited to either:
a) Importing axenic (sterile) nursery stock only, such as plants in-vitro; or
b) Testing and treating all plant material for these organisms either pre-export or
during post-entry quarantine in New Zealand.
While importing only plants in-vitro is possible for some species of plants, many plant
species have yet to be successfully placed into in-vitro culture, and the use of in-vitro culture
techniques is more costly than normal nursery systems. It is also difficult to envisage how
nursery stock could be effectively inspected or tested for the presence of such endophytic or
saprophytic organisms, as these organisms do not cause symptoms on the host plant material.
A number of blind tests would need to be performed to detect such organisms, and one would
never know if the correct testing methods had been used and whether or if all of the infesting
organisms had been detected. Crous and Groenewald (2005) stated that only an estimated
7% of the fungal species thought to exist are known. While tests may detect endophytic or
saprophytic organisms, in the majority of cases we would not be able to identify, for example,
the fungi to species level to allow any decisions to be made on the significance of the
organism to New Zealand.
There is also no single treatment available to sterilise nursery stock in-vivo while maintaining
plant viability.
The following principles should therefore be applied to the likely infestation of nursery stock
by endophytic or saprophytic organisms:
Page 26 of 193 14 March 2008 Import Risk Analysis: Wollemia nobilis (Wollemi Pine) Araucariaceae Nursery Stock from Australia