Questions and answers

• The review is required as part of Australia’s WTO obligations.
• Because a provisional quarantine pest status for Radopholus similis was recommended in the final import risk analysis report for fresh ginger from Fiji, Australia was required to review this status and provide justification for its decision.
• Australia made a commitment to undertake the review after the first year of trade.

• Currently, there is not enough scientific evidence to support the claim that Fiji has a strain of Radopholus similis with significantly different pathogenicity on ginger compared to the Radopholus similis already present in Australia.
• However, since the release of the draft report, the Queensland Department of Agriculture and Fisheries (QDAF) has confirmed its intention to undertake a comparative pathogenicity experiment in Australia. This is to determine if there are any differences in the economic impact on ginger yield and quality caused by Radopholus similis isolates from Fiji and Australia.
• The department will therefore maintain the current provisional quarantine pest status for Radopholus similis for an additional reasonable period of time so that this research can proceed, subject to a number of conditions. During this time period, the existing measures for Radopholus similis, recommended in the final IRA report, will remain in place.
• The final review report also proposes the introduction of a mandatory methyl bromide fumigation treatment for yam scale (Aspidiella hartii).

• The department and the technical experts representing the Australian ginger industry, QDAF and Fiji agree that the only way to scientifically prove such a difference would be to do an experiment directly comparing Fijian and Australian Radopholus similis isolates side-by-side in an appropriately controlled trial using a methodology agreed by all parties.
• Since the release of the draft report, QDAF has confirmed its intention to undertake such an experiment in Australia to determine if there are any differences in the economic impact on ginger yield and quality caused by Radopholus similis isolates from Fiji and Australia. Conduct of the experiment will be subject to the following conditions:
  • the availability of relevant Radopholus similis isolates
  • an agreed protocol for importation and appropriate quarantine containment
  • agreement by the Australian Ginger Industry Association, QDAF, Fiji and the department, on the experimental design and methodology
  • reasonable timeframes.

• Fresh ginger imported from Fiji has to meet Australia’s strict biosecurity standards. Specific import conditions are required by Australia to manage the identified biosecurity risks.
• All Fijian ginger consignments must meet Australia’s import conditions, have phytosanitary certification supplied by the Biosecurity Authority of Fiji and be inspected by the department on arrival in Australia.
• No live quarantine pests were detected on any of the consignments of fresh ginger imported from Fiji since trade commenced under the import conditions specified in the final import risk analysis report for fresh ginger from Fiji.
• Treated Fijian ginger therefore meets Australia’s appropriate level of protection as agreed to by Commonwealth and state governments and poses no biosecurity threat to the Australian ginger industry.

• Australia is a trading nation and our agricultural trading relationships are important to our economy and our agricultural industries.
• Every day Australia imports and exports thousands of tonnes of goods into and out of the country, including food.
• One of our key strengths as an agricultural trading nation is our clean and green reputation, underpinned by our science based biosecurity system.
• Our agricultural trade is supported by our robust biosecurity risk analysis, and we impose appropriate measures to mitigate risks.
• The department, in consultation with stakeholder-nominated technical experts, has reviewed the import conditions for fresh ginger from Fiji to manage the biosecurity risk to meet Australia’s Appropriate Level of Protection (ALOP).
• Australia’s ALOP is expressed as “a high level of Sanitary and Phytosanitary protection aimed at reducing biosecurity risks to a very low level, but not to zero”.

• The Australian ginger industry raised this as a concern during the review process and previously during the process of consultation on the import risk analysis for fresh ginger from Fiji.
• The import risk analysis took the risk of diversion for planting into account.
• The Australian industry remains vulnerable to the impacts of a range of diseases including those caused by Pythium and Fusarium spp. which can be introduced to crops through planting material. These diseases are already present in Australia.
• The Australian ginger industry is likely to benefit from a high health seed scheme to reduce the likelihood that any ginger rhizomes (local or imported) purchased from markets would be planted by growers.
• Other plant industries such as potatoes and strawberries have developed clean seed schemes to provide their industries with a secure source of quality seed.

• This would be difficult to enforce from a regulatory perspective.
• Prosecuting consumers who have planted ginger purchased from the supermarket presents practical difficulties.
• Permit holders who import ginger for consumption but divert it to planting could potentially be prosecuted for breaching their import permit conditions however historically such cases have been very difficult to prosecute.

• Yes. All food sold in Australia must satisfy Australia’s food standards. Australian law requires that all food, including imported fresh fruit, meet the standards set out in the Australia New Zealand Food Standards Code.

• Australia is entitled to take precaution into account. However the World Trade Organization (WTO) rules that govern international trade cannot be disregarded.
• The relevant WTO rules in relation to sanitary and phytosanitary measures are set out in the SPS Agreement. Any import restrictions must only be applied to the extent necessary, must be based on scientific principles and must not be maintained without sufficient scientific evidence.
• Article 5.7 of the SPS Agreement provides that where scientific evidence is insufficient, provisional measures may be adopted, but in such circumstances the WTO Member adopting the measure must seek to obtain the additional information necessary for an objective assessment of the risk, and must review the SPS measure, within a reasonable period of time.

• Pests and diseases present in Australia already pose a significant challenge for the domestic ginger industry. The department understands that significant crop losses have resulted from Pythium myriotylum, Fusarium oxysporum f.sp. zingiberi, Meloidogyne incognita, Meloidogyne javanica and other pests, all of which could be curtailed through greater use of clean seed. Extension programs are a responsibility of state agriculture departments, so QDAF may wish to further explore the establishment of such a scheme.

• Methyl bromide is a broad spectrum fumigant that has been used in production systems and as a treatment to manage a wide range of pests in both imports and exports for many years. It has an extensive international history of effective use for quarantine purposes and its efficacy is well understood. It is accepted as an effective fumigant for surface pests, and can also penetrate some distance into the commodity being treated, including ginger rhizomes.
• The presence of live root knot nematodes (Meloidogyne spp.) in a consignment of fresh ginger from Fiji in September 2014 raised questions about the efficacy of methyl bromide as a quarantine treatment. The Meloidogyne species associated with ginger in Fiji are not quarantine pests for Australia, as they are already present in Australia and are not regulated. Methyl bromide fumigation would not be prescribed as a treatment for exotic Meloidogyne spp. in imported produce, as it is known not to be fully effective against these pests.
• Evidence gathered from independent testing of imported ginger from Fiji indicates that Radopholus similis is being effectively managed through existing commercial production processes, including crop rotation, use of hot water treatment of seed ginger, field hygiene, and quality control during pre-export preparation. In addition, there is a pre-export phytosanitary inspection by BAF and an on-arrival inspection by the department to verify that ginger rhizomes are not infested with quarantine pests.
• These commercial production and verification processes actively reduce the likelihood of infested rhizomes entering the export chain. In addition, recent surveys in Fiji have not detected Radopholus similis.  If present then it is at very low levels, and any infection is most likely to occur on or near the surface of a ginger rhizome. The nematodes would be killed by the methyl bromide fumigation treatment.
• The department is satisfied that an appropriate level of protection is being achieved on imported Fiji ginger. This is not expected to change in the short term, particularly during the additional time period during which QDAF proposes to conduct their experiment.

It was suggested that species divergence explains different observed behaviours in Radopholus similis, given the limited number of introductions into Australia and Fiji and resulting lack of genetic diversity within populations.

Population changes due to genetic changes are possible. However, the ability to survive in a diverse range of environments and on different hosts may be an inherent characteristic that exists in all populations of this highly polyphagous and successful pest species. Phenotypic differences are expected within and between natural populations due to a range of genetic and non-genetic factors. Laboratory studies showing phenotypic differences between populations in measures of pathogenicity do not therefore necessarily support the existence of ‘strains’.

Radopholus similis has been introduced into most tropical and subtropical regions where bananas are grown, mainly spread via movement of banana corms. A number of other plants are known to be suitable as hosts, and a wide host range has long been recognised. It has shown great capacity to adapt to new geographically diverse locations where suitable conditions exist (including in glasshouses in colder regions). Pathogenicity on banana is consistently reported; pathogenicity on other hosts is more irregular, depending on the complex interrelationship between the host, environment, land management and cultural practices regulating nematode numbers.

It is important to keep in mind that ginger parasitism in Fiji’s Radopholus similis population is not unique, as ginger is also reported as a host in other countries. As a polyphagous pest, Radopholus similis was already genetically capable of feeding and reproducing on ginger, but until large numbers of nematodes were introduced into ginger farms, this would have largely gone unnoticed.

It should also not be overlooked that Radopholus similis has been found in ginger in Australia previously (but not formally reported), and the first QDAF ginger experiment in 2012 showed that an Australian isolate survived and reproduced capably in ginger.

This is true. However, populations are expected to be variable. Phenotypic differences are expected within and between natural populations due to a range of genetic and non-genetic factors that influence pathogenicity. In the absence of any information to suggest there are significant genetic differences between populations, observed differences between individual populations may simply be due to the natural variability that exists across all populations rather than due to a fixed ‘strain’ difference resulting from a unique adaptive trait.

Ginger parasitism by Radopholus similis is not unique to Fiji, and the pest has been reported affecting ginger crops in a number of geographically different locations globally. Is this more likely to suggest multiple independent adaptations of a feeding preference for ginger; or, alternatively, is the observed polyphagy indicative of the phenotypic plasticity that already exists in this species, where different host preferences can be expressed under suitable conditions in different locations without genetic changes?

The ‘switch’ from banana to ginger in Fiji happened rapidly, when banana plantations were cleared and replanted with ginger. This does not necessarily indicate that significant evolutionary change was involved. Radopholus similis can survive for a short period on volunteer plants or weeds, but it survives poorly in the absence of good hosts, typically disappearing within six to twelve months. Its ‘switch’ to ginger may therefore have simply been opportunistic.

The report’s citation of Marin et al. (1999) as evidence that the Radopholus similis genome is highly conserved was questioned, because that research was based on RAPD analysis. This research predates the use of whole genome sequence comparisons, and so should be ‘carefully considered’ before drawing conclusions.

It is agreed that RAPD has numerous shortcomings. However, most of the research on population variability in Radopholus similis has used Random Amplified Polymorphic DNA (RAPD) analysis. Very little comparative research of different populations using DNA sequences has been done. Research from studies using RAPD is still widely cited in recent literature.

The article by Marin et al. (1999) frequently uses phrases such as “considerable genome similarity” (p232), “high degree of similarity” (p235), “highly similar” (p235), “high level of genome conservation” (p235, and again on p236), “highly conserved nature of the Radopholus genome” (p236), “high levels of genome similarity” (p237), “high level of molecular and morphological similarity” (p238) and “high degree of genome conservation” (p238). The claim that the Radopholus similis genome is not highly conserved is not supported by this article.

The AUSVEG submission presents some genome homology results for comparison with a genetic similarity index determined by Marin et al. (1999), which was obtained by hierarchical cluster analysis using simple matching coefficients. These two analyses have completely different methodological and statistical bases, so no such direct comparison can be made.

While not comparing full genomes, Tan et al. (2010) examined internal transcribed spacer (ITS) ribosomal deoxyribonucleic acid (rDNA) sequences of multiple Radopholus similis populations worldwide. They found identical sequences in 32 isolates from Australia, Costa Rica, China, South Africa, Ghana, Sudan, Panama, Uganda, Guinea, Cuba, Belgium and Germany, as well as a number from sources of unknown origin. A further 15 isolates from Costa Rica, Colombia, China, Malaysia, Guinea and Germany differed from the other 32 isolates by only one mutation. This indicates there is little genetic variability between numerous geographically isolated populations.

It was suggested that the Radopholus similis mitochondrial DNA (mtDNA) described by Jacob et al. (2009) ‘displays a unique gene order, absence of transcript polyadenylation and lack of canonical stop codons, which may all account for pathogenicity differences between populations and potential for adaptation’.

Jacob et al. (2009) have made no inference about intraspecific variability in the mtDNA of Radopholus similis. The study only involved a single nematode culture, of unstated origin. This paper does not discuss differences in mtDNA sequences between populations in different geographical regions. The paper also does not discuss pathogenicity or host preference. No conclusions about intraspecific variation can be drawn from this paper, certainly not in relation to supposed differences in host preference or pathogenicity.

The department is not aware of any research that has examined the mtDNA sequences of populations in Australia or Fiji. No evidence has been provided to indicate there are known differences in mtDNA between populations of Radopholus similis in Fiji and Australia.

The function of mtDNA is predominantly related to cellular energy production. Most mtDNA genes are responsible for producing transfer RNA (tRNA) and ribosomal RNA (rRNA), which are involved in assembling proteins from amino acids. The other mtDNA genes are responsible for producing the enzymes involved in mitochondrial oxidative phosphorylation.

The department is not aware of any research that has linked variation in mtDNA to pathogenicity in Radopholus similis. Additionally, it is not clear how variation in mtDNA would have any influence on host preference.

A recent paper by Li et al. (2015) described the RS-crt gene in Radopholus similis, which is responsible for encoding the multifunctional protein calreticulin (CRT). The CRT gene is highly conserved in plants and animals (including humans), and plays a role in skin penetration, infection, parasitism, pathogenesis and immune invasion (Li et al. 2015). This research was published just prior to the release of the draft review report, so discussion of this study was not included in the report.

Li et al. (2015) make no inference about variability in pathogenicity or host preference. The research only examined a single cultured nematode isolate, which was originally collected from the roots of Anthurium andraeanum at an unspecified location. It notes that Rs-crt expression was reduced in nematodes feeding on transgenic tomato plants that were specifically engineered for this purpose (that is, to interfere with the expression of the Rs-crt gene). It is debateable whether RS-crt can really be characterised as a ‘pathogenicity gene’.

It is important to note that Australia’s Radopholus similis are highly pathogenic pests on banana, which would suggest they have a functional Rs-crt gene, and significant differences in gene expression compared to other populations internationally would not be expected.

Jacob, JEM, Vanholme, B, Van Leeuwen, T and Gheysen, G 2009, A unique genetic code change in the mitochondrial genome of the parasitic nematode Radopholus similis, BMC Research Notes, vol. 2:192. http://www.biomedcentral.com/1756-0500/2/192

Li, Y, Wang, K, Xie, H, Wang, YT, Xu, CL, Huang, X and Wang, DS 2015, A nematode calreticulin, Rs-CRT, is a key effector in reproduction and pathogenicity of Radopholus similis, PLoS One 10(6): e0129351, doi:10.1371/journal.pone.0129351.

Marin, DH, Barker, KR, Kaplan, DT, Sutton, TB and Opperman, CH 1999, Aggressiveness and damage potential of Central American and Caribbean Populations of Radopholus spp. in banana, Journal of Nematology, 31, pp. 377–385.

Tan, M, Cobon, J, Aitken, E and Cook, LG 2010, Support for the out-of-Southeast Asia hypothesis for the Australian populations of Radopholus similis (Cobb, 1893)(Nematoda: Pratylenchidae), Systematic Parasitology 77, pp. 175–183.