Risk Assessment and Risk Management Plan


Section 3 Conclusions regarding weediness



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Section 3 Conclusions regarding weediness


  1. It is concluded that the down-regulation of ethylene biosynthesis, the modification to ethylene perception and the other introduced genes are unlikely to affect attributes of the GM papayas proposed for release that may alter potential weediness.

  2. Aspects of the proposed release supporting this consideration are that:

  1. However, further information on the impact of the genetic modifications on attributes of GM papayas that may affect their weediness (eg. dormancy of seeds, competitive ability, susceptibility to natural enemies and spread within the environment) would be required before the Regulator could determine this conclusively. This information would be required before a larger scale or less stringently controlled release could be considered (see Chapter 2, section 3).

  1. In addition, it is further concluded that the low risk of weediness could be managed to an acceptable level by implementing various strategies to minimise the spread and persistence of GM papayas in the environment. As proposed by the applicant, these strategies include:

  • restricting the proposed release to one hectare; and

  • preventing dispersal of the GM papaya seeds by containing the release in an insect-proof enclosure that also prevents larger animals accessing the GM plants and their fruit.

  1. Details of these and other risk management conditions relating to the potential weediness of the GM papayas proposed for release are provided in Appendix 6.

APPENDIX 4 ENVIRONMENTAL SAFETY - Transfer of introduced genes to other organisms


  1. Under section 51 of the Act, the Regulator is required to consider risks to human health and safety and the environment in preparing the risk assessment and the risk management plan. Appendices 2 - 4 consider potential hazards that may be posed to the environment. The potential for gene transfer from the GM papayas to other organisms is considered in this Appendix.

  2. Gene transfer is the movement of genes between individuals. Within a species, genes are routinely exchanged between individuals of successive generations through sexual reproduction in animals, cross pollination in plants and conjugation in bacteria. Hybrids can be produced between closely related species. In plants, for example cross pollination of wheat and rye produces triticale, in animals sexual reproduction of a horse and a donkey produces a mule. Hybrid progeny may be fertile or sterile, meaning that hybridisation may or may not lead to the introgression of a gene or genes into a population. Gene transfer is not readily observed between distantly related species. However, gene transfer between sexually incompatible organisms can occur. Reconstruction of ‘family trees’ based on DNA sequence similarities reveals that ancestral plants have occasionally exchanged small DNA fragments with distantly related organisms. In general, there seems to have been only very limited transfer of genes from plants to other types of organisms.

  3. For ease of reference, the assessment of gene transfer to other organisms is presented in four main sections:

  • Section 1 details the nature and likelihood of genes introduced to the GM papayas transferring to other plants, including to other papayas;

  • Section 2 details the nature and likelihood of genes introduced to the GM papayas transferring to microorganisms;

  • Section 3 details the nature and likelihood of genes introduced to the GM papayas transferring to animals, including humans; and

  • Section 4 provides conclusions regarding the gene transfer hazard with respect to the issues considered in each of the sections 1-3.

  1. In general terms, the types of hazards that might result from transfer of the genes introduced into the GM papayas to other organisms include the production of plants with delayed fruit ripening or other attributes associated with ethylene production or perception such as altered responses to soil microbes, modified germination characteristics or increased leaf area. Such plants may then develop an advantage in the natural environment with potential to reduce native biodiversity or disrupt ecosystem structure and function. Another potential hazard is the transfer of the antibiotic resistance genes to pathogens which may generate antibiotic-resistant pathogens with potential to harm human or animal health.

Section 1 Transfer of introduced genes to other plants


Section 1.1 Nature of the gene transfer hazard

1.1.1 Transfer of genes to other papayas


  1. Transfer of the introduced genes or regulatory sequences to other papaya plants would present the same hazards and have the same potential impacts as the presence of the genes in the GM papayas proposed for release (see Appendices 2 and 3). Gene transfer to non-GM papaya by cross-pollination is very likely to produce seeds containing the inserted genes and, if these germinate and establish, would most probably result in papaya plants with similar traits to the GM papayas proposed for release.

  2. If transfer occurred to papaya plantations, domestically cultivated papaya trees or naturalised papaya populations, this would increase the possibility that the genes would persist in the environment. The flow-on impacts of such transfer would depend on whether the inserted genes confer a selective advantage, potentially enhancing weediness of papaya in Australia (see Appendix 3), or whether the inserted genes affect the toxicity or allergenicity of papaya which may affect the safety of humans or other organisms that may consume or handle the fruit or other tissues derived from the GM papayas.

1.1.2 Transfer of genes to other plant species


  1. Transfer of the introduced genes or regulatory sequences into other plant species, in particular to native flora, may have adverse effects on biodiversity. Other potential hazards specific to the transferred gene sequences are as follows:

  • ACC synthase genes and related constructs:

All plant species have ACC synthase genes. It is thus theoretically possible, that if gene transfer of the capacs 1 or capacs 2 gene silencing constructs to other plant species occurred, these constructs could initiate silencing of endogenous ACC synthase genes in other plant species. The likelihood of this occurring depends on the degree of DNA sequence homology between the capacs 1 or capacs 2 genes and the ACC synthase genes in other plant species.
Plants could thus have down-regulation of endogenous ethylene production, which may delay ethylene-related processes, particularly floral senescence and fruit ripening. In the unlikely event of this occurring, there is a very low possibility that it may decrease the attractiveness of such plants to natural enemies (herbivores and pathogens) or enhance their ability to compete with other plants, with potential consequences for weediness.



  • etr1 1 gene:

Plants could become insensitive to ethylene. This may delay or prevent maturation of fruit or affect other ethylene-related processes in the plant including, for example, responses to pathogens or promotion of seed germination, as summarised in Appendix 1, Section 3.2. These aspects of plant biology have potential to affect weediness.



  • Antibiotic resistance and reporter genes:

Plants could become resistant to the antibiotics or produce the GUS protein. Antibiotic resistance would only have an impact if the antibiotics were used for control of the plants. The antibiotics in question (nptII and bla) were used in the laboratory solely to select for genetically modified cells or plants and are not applied to plants outside the laboratory. Note that although nptII is expressed in the GM papayas proposed for release, bla is under the control of a bacterial promoter and is not expressed in the GM plants because the promoter that is required for its expression is not active in plants. Note, also, that GUS expression is unlikely to be toxic or allergenic (Appendix 2) and is unlikely to affect the weediness (Appendix 3).


  • CaMV 35S promoters and other regulatory sequences:

If gene transfer did occur, there could be unintended or unexpected effects if the introduced regulatory sequences altered the expression of endogenous plant genes. If such perturbation of normal plant gene expression occurred, the impact would depend on the phenotype.

One of these regulatory sequences is derived from a plant pathogen (Agrobacterium tumefaciens). The possibility has been considered that it may have pathogenic properties.



Section 1.2 Likelihood of gene transfer to other papayas, or other plant species

  1. The most likely means by which the inserted genes could be transferred to other plants is by cross-pollination (out-crossing). It has been well-demonstrated that hawkmoths (family Sphingidae) are the primary pollinators of papaya in Australia and that other agents, including bees and wind, are of little, if any, importance (Garrett 1995; Morrisen et al. 2003; OGTR 2003). Hawkmoths potentially provide, therefore, the most likely means by which pollen could be transferred to non-GM papayas or to other plant species. The likelihood of transfer to non-GM papayas would be affected by several variables including the relationship between pollinator foraging ranges and the distance between papaya trees. There appear to be no published data on the typical foraging ranges of sphingids, but their foraging behaviour does not appear do be affected by wind direction (Garrett 1995).

  2. For a detailed consideration of the likelihood of gene transfer from papayas, including an overview of the pollination biology of papaya, see the document, ‘The Biology and Ecology of Papaya (paw paw), Carica papaya L., in Australia’ that was produced in order to inform this risk assessment process. This document is available at the OGTR website (http://www.ogtr.gov.au).

  3. In summary, the likelihood of gene transfer to other species, including papaya’s closest relatives in the genus Vasconcella, is negligible because of substantial genetic incompatibility. Moreover, although these close relatives may be available horticulturally, key literature (e.g. Elliot and Jones 1980) does not reference them or recommend their cultivation, and there is no evidence that they occur widely in Australia. Well-demonstrated genetic differences also limit gene transfer to more distantly related plant genera.

  4. Proximity to other papayas

  5. Other than six non-GM papaya trees grown about 200 m from the proposed release site elsewhere on the Queensland Department of Primary Industries research station at Redlands, Queensland, the closest papaya trees occur in domestic gardens, about 500 m from the release area. The closest commercial papaya plantation is located 12.5 km from the proposed release site (information provided by the applicant). There are 50-60 km between the proposed release area and the nearest known naturalised papaya population (Australia’s Virtual Herbarium 2003), which was recorded from the southern slopes of Mt Beerburrum, near Caloundra, in south-east Queensland. Both the commercial plantation and the naturalised population are unlikely to be within foraging range of any pollinators that may access the GM papayas proposed for release.

  6. Irrespective of the distances between the proposed release site and other non-GM papayas, the licence requires the applicant to enclose the entire release site in a self-supporting insect-proof enclosure secured at ground level, that prevents the movement of known papaya pollinators into, and from, the enclosure. In addition, the licence requires that the enclosure is monitored every day for breaches of its integrity and that any such breaches are repaired immediately. The licence also requires that any male flowers produced by the GM papayas are removed prior to opening. These measures would limit the likelihood of gene transfer to other papayas to negligible levels.

  7. The consultation version of the risk assessment and risk management plan included a risk management measure to bag hermaphrodite flowers to minimise the unlikely potential for gene transfer from the GM papayas. Advice received from the applicant indicated that bagging hermaphrodite flowers was likely to affect the experimental objectives of the release by damaging developing flowers and fruit. In addition, the applicant submitted that the bagging was unnecessary and not warranted, given the requirement to contain the trial in an insect-proof enclosure that prevents pollen movement out of the release area by pollinators, and the assessment of a low level of risk posed by the proposed dealing in the unlikely event of such pollen movement occurring.

  8. In relation to the applicant’s submission, it is significant that available evidence clearly demonstrates that in Queensland, papaya flowers are rarely, if ever, successfully pollinated by wind-dispersed pollen (Garrett 1995; OGTR 2003). The insect-proof enclosure is likely to further lower the likelihood of successful wind pollination, particularly because papaya pollen is sticky or powdery (see Garrett 1995) and, thereby, unlikely to be blown through the insect-proof netting.

  9. In consultation with GTTAC members it was determined that the risk of gene transfer from the GM papayas could be managed effectively without bagging hermaphrodite flowers, so long as the frequency with which the insect-proof enclosure is inspected for damage is increased from twice per week to daily, that any damage is repaired immediately and that if damage cannot be repaired immediately, flowers and fruits from the GM papayas are removed and destroyed to prevent the potential for pollen or seed movement from the release site.

  10. Accordingly, the proposed condition to bag hermaphrodite flowers has been removed and the licence now requires the UQ to inspect the insect-proof enclosure for damage every day and to repair any damage immediately. If the damage cannot be repaired immediately, the licence then requires that flowers and fruits from the GM papayas are immediately removed and destroyed.



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