Draft pest risk analysis report for ‘

5 Risk assessments for pathways

The risk assessments in this section focus on the major pathways identified for the potential introduction of ‘Ca. L. psyllaurous’ associated with Solanaceae crops.

The probability of entry has been considered individually for each pathway as the pathway by which ‘Ca. L. psyllaurous’ might enter Australia has a significant effect on these assessments. However, the probabilities of establishment and spread and the assessment of potential consequences have been assessed only once for the pathways considered here. This is because the probabilities of establishment and spread and the potential consequences consider post–border issues that are influenced by the susceptibility of hosts, the availability of hosts and the suitability of the environment in Australia for the pathogen.

5.1 Probability of entry

The risk assessment in this section focuses on the four pathways identified for the potential entry of ‘Candidatus Liberibacter psyllaurous’:

• 
  fruit (including seed)
  
• 
  potato tubers
  
• 
  nursery stock
  
• 
  tomato-potato psyllids (Bactericera cockerelli).
  

5.1.1 Pathway 1 – Fruit (including seed)

The likelihood that ‘Ca. L. psyllaurous’ will arrive in Australia with the trade in fresh fruit of known hosts, including their seeds: HIGH.

• 
  ‘Candidatus Liberibacter psyllaurous’ is known to infect capsicum, tomato, cape gooseberry, tamarillo and potato (MAFBNZ 2008).
  
• 
  Both the plants and the fruits can be infected by ‘Ca. L. psyllaurous’ and the bacterium has been detected in tomato fruits (MAFBNZ 2008).
  
• 
  Fruit infected by ‘Ca. L. psyllaurous’ are small, misshapen, with a strawberry–like appearance, and display uneven development of fruit locules (MAFBNZ 2008). Symptomatic fruit infected by ‘Ca. L. psyllaurous’ is likely to be removed during grading operations.
  

• 
  Furthermore, the bacterium would not be removed by standard post-harvest treatments, such as washing and brushing the fruit.
  
• 
  New Zealand researchers have investigated the potential for ‘Ca. L. psyllaurous’ to be transmitted through seed. Based on PCR testing, all parts of the fruit were found to contain the bacterium, including parts of the seed (MAFBNZ 2008).
  
• 
  Good storage temperatures for tomatoes range from 7°C (90–95% humidity) for red ripe tomatoes to 13°C for mature green tomatoes (90–95% humidity) (PeakFresh 2008). These storage conditions are unlikely to have any significant impact on the level of ‘Ca. L. psyllaurous’ in tomato or any other imported fruits.
  
• 
  Tomatoes are highly perishable so short transport periods are necessary. Transport of fruit to Australia by either air or sea freight takes from a few hours to one week (Agribusiness Information Centre 2009). The short time from field to market also suggests that there would be little or no change in bacterial viability during post harvest transport and storage.
  

The likelihood that ‘Ca. L. psyllaurous’ will be distributed within Australia in a viable state with imported fruit and transferred to a suitable host: EXTREMELY LOW.

• 
  Fruits from ‘Ca. L. psyllaurous’ host plants will be distributed for retail sale to multiple destinations within the PRA area, so a portion of the fruit is likely to reach areas of host abundance.
  
• 
  Hosts of ‘Ca. L. psyllaurous’ include capsicum, tomato, cape gooseberry, tamarillo and potato (MAFBNZ 2008). These species are widely distributed in commercial and domestic environments within Australia. The susceptibility of other members of the Solanaceae family to ‘Ca. L. psyllaurous’ requires further investigation.
  
• 
  Fruit infected by ‘Ca. L. psyllaurous’ is small, misshapen, with a strawberry–like appearance, and display uneven development of fruit locules (Liefting et al. 2009). Symptomatic fruits are likely to be considered unmarketable by wholesalers and retailers. These fruits may be disposed of with general garbage or in compost bins before sale.
  
• 
  Asymptomatic fruit in sound condition would be distributed and sold through markets and retail chains.
  
• 
  Although the intended use of fresh fruit is human consumption, waste material would be generated (e.g. overripe and damaged fruit, uneaten portions). Whole or parts of the fruit may be disposed of at multiple locations throughout Australia in compost bins or amongst general household waste.
  

• 
  There is no evidence that the tomato-potato psyllid is present in Australia.
  
• 
  Only three psyllid species are known to vector ‘Ca. Liberibacter’ species. In the field, the Asian citrus psyllid (Diaphorina citri) vectors ‘Ca. L. asiaticus’ and ‘Ca. L. americanum’ (Yamamoto et al. 2006), the African citrus psyllid (Trioza erytreae) vectors of ‘Ca. L. africanus’ (Aubert 1987) and the tomato-potato psyllid (B. cockerelli) vectors ‘Ca. L. psyllaurous’ (Hansen et al. 2008). This vector specificity suggests it is very unlikely that Australian native psyllids would be able to vector ‘Ca. L. psyllaurous’.
  
• 
  Furthermore, there are no species in the genus Bactericera in Australia and the only known member of the Triozidae or Psyllidae families reported feeding on a solanaceous host in Australia is an undescribed species of Acizzia that feeds on eggplant (Kent 2008).
  
• 
  Graft transmission has been demonstrated for ‘Ca. L. psyllaurous’ in trials in New Zealand (MAFBNZ 2008) but fruit and fruit truss material is not suitable for grafting.
  
• 
  Seed transmission trials found no ‘Ca. L. psyllaurous’ infection in 1030 tomato seedlings, 225 capsicum seedlings and 225 tamarillo seedlings raised from seed from infected fruit (Liefting 2008a), indicating that ‘Ca. L. psyllaurous’ is not seed-transmitted, at least at the frequency that would have been detected in these experiments. Therefore, it is unlikely that plants infected with ‘Ca. L. psyllaurous’ would establish from seed from imported fruit of host species.
  

5.1.2 Pathway 2 – Potato tubers

The likelihood that ‘Ca. L. psyllaurous’ will arrive in Australia with trade in fresh potato tubers for consumption: HIGH.

• 
  ‘Candidatus Liberibacter psyllaurous’ is known to infect all parts of potato plants, including the tubers (MAFBNZ 2008).
  
• 
  Potato tubers infected by ‘Ca. L. psyllaurous’ have a brown discolouration of the vascular ring and necrotic flecking of internal tuber tissues (MAFBNZ 2008). Internal symptoms may be difficult to detect at harvest or during post-harvest grading operations.
  
• 
  The characteristic symptom of ‘Ca. L. psyllaurous’ infection is a striped pattern of discolouration that occurs only after the potato tuber is cooked. This symptom would not be apparent at the time of import.
  

Draft PRA report for ‘Candidatus Liberibacter psyllaurous’ Risk assessments for pathways

• 
  Furthermore, the bacterium would not be removed by standard post-harvest treatments, such as washing and brushing.
  
• 
  Potato tubers for the fresh market are generally stored at 4–6°C and those for processing at 7–10°C, with a relative humidity of 95% or above (DPIW 2007; Holley 2003). It is unknown what affect these storage conditions would have on the level of ‘Ca. L. psyllaurous’ infection in potato tubers but they are not expected to eliminate the bacterium from the tubers.
  

The likelihood that ‘Ca. L. psyllaurous’ will be distributed within Australia in a viable state with imported potato tubers and transferred to a suitable host: MODERATE.

• 
  Potato tubers for consumption will be distributed for retail sale to multiple destinations within Australia.
  
• 
  Potato tubers infected by ‘Ca. L. psyllaurous’ have a brown discolouration of the vascular ring and necrotic flecking of internal tuber tissues (MAFBNZ 2008). Internal symptoms may not be detected during distribution and retail sale.
  
• 
  The characteristic symptom of ‘Ca. L. psyllaurous’ infection is a striped pattern of discolouration that occurs only after the potato tuber is cooked. This symptom would not be apparent at the point of sale of the fresh commodity.
  
• 
  Infected tubers in apparently sound condition would be distributed and sold through markets and retail chains.
  
• 
  Although the intended use of potato tubers is human consumption, waste material would be generated (e.g. sprouting and damaged tubers). Whole or parts of potato tubers could be planted or disposed of at multiple locations throughout Australia in compost bins or amongst general household waste.
  
• 
  An important tuber characteristic of tuber infection is a loss of dormancy, resulting in premature sprouting and the production of very weak, spindly sprouts (UNL 2009). These tubers are unlikely to be planted or produce daughter plants, reducing the probability of the distribution of the bacterium.
  
• 
  The only known vector of ‘Ca. L. psyllaurous’ is the tomato-potato psyllid (Bactericera cockerelli) (Hansen et al. 2008). There is no evidence that this psyllid is present in Australia. There is also no evidence to suggest that this psyllid feeds on potato tubers or can acquire the bacterium from feeding on potato tubers.
  

Draft PRA report for ‘Candidatus Liberibacter psyllaurous’ Risk assessments for pathways

• 
  Furthermore, there are no species in the genus Bactericera in Australia and the only known member of the Triozidae or Psyllidae families reported feeding on a solanaceous host in Australia is an undescribed species of Acizzia that feeds on eggplant (Kent 2008).
  
• 
  For ‘Ca. L. psyllaurous’ to be distributed through infected tubers, they must be able to grow and produce infected plants. Shapovalov (1929) suggests that ‘Ca. L. psyllaurous’ infection can be transmitted with potato tubers. That is, infected tubers can produce rise to infected plants.
  
• 
  It is therefore possible for the bacterium to be distributed within Australia with the planting or disposal of infected tubers into locations where they can grow, without the aid of its psyllid vector.
  

5.1.3 Pathway 3 – Nursery stock

The likelihood that ‘Ca. L. psyllaurous’ will arrive in Australia with the importation of nursery stock: HIGH.

• 
  Nursery stock is significantly different from other commodities such as fruit, in that nursery stock can support all life stages of pests associated with it. Many of these are able to develop, reproduce and complete their life cycle without leaving the host.
  
• 
  ‘Candidatus L. psyllaurous’ can be associated with all vegetative parts of host plants (MAFBNZ 2008), so nursery stock of host plants can be infected and provide a pathway for the importation of the bacterium into Australia.
  
• 
  The bacterium is known to infect capsicum, tomato, cape gooseberry, tamarillo and potato (MAFBNZ 2008).
  
• 
  Of these known hosts of ‘Ca. L. psyllaurous’, nursery stock of cape gooseberry, potato and tamarillo is permitted entry to Australia (Table 1.1).
  
• 
  ‘Candidatus L. psyllaurous’ is a newly described pathogen (Hansen et al. 2008), and it is likely that further hosts will be identified in the future. These are likely to occur in the Solanaceae, Convolvulaceae or Lamiaceae, as the known vector of the bacterium, the tomato-potato psyllid, reproduces on a wide range of hosts in these families (Appendix A). Nursery stock of a number of these hosts is permitted entry to Australia (Appendix A).
  
• 
  Plants infected by ‘Ca. L. psyllaurous’ show various symptoms including shortened petioles, chlorotic leaves and a sharp tapering of the leaf apex (spiky appearance) leading to leaf cupping (MAFBNZ 2008). Symptomatic nursery stock will be detected on arrival in Australia.
  

• 
  It has also been noted that ‘Ca. L. psyllaurous’ infected plants may be asymptomatic (MAFBNZ 2008). Symptoms are thought to be induced by environment (temperature) and growing conditions (glasshouse or field grown, soil moisture and nutrients).
  
• 
  It is likely that asymptomatic plants infected by ‘Ca. L. psyllaurous’ would pass routine visual inspections and be released from quarantine into Australia.
  
• 
  Nursery stock is expected to be shipped at moderate temperatures and humidity levels to ensure its survival. These conditions are unlikely to adversely affect ‘Ca. L. psyllaurous’ during shipment.
  

The likelihood that ‘Ca. L. psyllaurous’ will be distributed within Australia in a viable state with imported nursery stock and transferred to a suitable host: HIGH.

• 
  Nursery stock is imported into Australia for propagation in nurseries for sale and distribution to multiple destinations within Australia.
  
• 
  Plants produced from the nursery stock will be planted directly into suitable habitats to grow.
  
• 
  As nursery stock may not display symptoms of ‘Ca. L. psyllaurous’ infection, there is a risk that infected material would be used for propagation.
  
• 
  ‘Candidatus Liberibacter’ species are spread through propagation (Polek et al. 2007). Graft transmission has been proven for ‘Ca. L. psyllaurous’ in trials undertaken in New Zealand (MAFBNZ 2008).
  
• 
  Production of nursery stock of cape gooseberry, tamarillo and other solanaceous plants would be by cuttings and grafts.
  
• 
  The only known vector of ‘Ca. L. psyllaurous’ is the tomato-potato psyllid (Hansen et al. 2008). There is no evidence that this psyllid is present in Australia.
  
• 
  Only three psyllid species are known to vector ‘Ca. Liberibacter’ species. In the field, the Asian citrus psyllid (Diaphorina citri) vectors ‘Ca. L. asiaticus’ and ‘Ca. L. americanum’ (Yamamoto et al. 2006), the African citrus psyllid (Trioza erytreae) vectors of ‘Ca. L. africanus’ (Aubert 1987) and the tomato-potato psyllid (B. cockerelli) vectors ‘Ca. L. psyllaurous’ (Hansen et al. 2008). This vector specificity suggests it is very unlikely that Australian native psyllids would be able to vector ‘Ca. L. psyllaurous’.
  
• 
  Furthermore, there are no species in the genus Bactericera in Australia and the only member of the Triozidae or Psyllidae families reported feeding on a solanaceous host in Australia is an undescribed species of Acizzia that feeds on eggplant (Kent 2008).
  
• 
  As there are no known vectors of ‘Ca. L. psyllaurous’ in Australia, the only pathway for the distribution of the bacterium in nursery stock is the planting of infected plants into suitable habitats for their growth.
  

The association of ‘Ca. L. psyllaurous’ with nursery stock and the likely distribution of infected plants to multiple locations support an assessment of ‘high’ for the distribution of this species in nursery stock.

5.1.4 Pathway 4 – Tomato-potato psyllid

The likelihood that tomato-potato psyllids infected with ‘Ca. L. psyllaurous’ will arrive in Australia with trade in fresh fruit or nursery stock of host species of the Solanaceae family: HIGH.

• 
  Bactericera cockerelli is the only known insect vector of ‘Ca. L. psyllaurous’ (Hansen et al. 2008). The psyllid acquires the bacterium by feeding on infected host plants.
  
• 
  ‘Candidatus L. psyllaurous’ host plants include capsicum, tomato, cape gooseberry, tamarillo and potato (MAFBNZ 2008).
  
• 
  Bactericera cockerelli is reportedly able to develop, reproduce and complete its life cycle on all known hosts of ‘Ca. L. psyllaurous’ (NZCOP 2008; Wallis 1955; Knowlton and Thomas 1934).
  
• 
  Hosts of ‘Ca. L. psyllaurous’, such as tomato, potato and capsicum, are preferred by B. cockerelli. This makes it more likely that psyllids entering Australia from ‘Ca. L. psyllaurous’ affected areas would be infected with the bacterium.
  
• 
  Bactericera cockerelli feeds on a wide range of plants, which includes species in 20 plant families, but the psyllid only breeds on species in the Solanaceae, Convolvulaceae and Lamiaceae (Wallis 1955). It would be possible for infected psyllids to enter Australia via trade in commodities, such as fresh fruit and nursery stock, of any of these species but is more likely to be associated with host species.
  
• 
  A number of consignments of yellow bell and red bell peppers arriving in Hawaii from Los Angeles were infested with the tomato-potato psyllid (HDOA E-News 2004).
  
• 
  Nursery stock represents a higher risk than fruit, as nursery stock of host species supports all life stages of the psyllid. Adult female B. cockerelli lay their eggs on the leaves of host plants and nymphs are commonly found on the underside of the leaf (Horticulture New Zealand 2009). Therefore, propagative material from ‘Ca. L. psyllaurous’ affected areas may harbour infected B. cockerelli eggs, nymphs and/or adults.
  
• 
  ‘Candidatus L. psyllaurous’ can infect all life stages of the psyllid, including eggs (Hansen et al. 2008). Bactericera cockerelli eggs are quite small and may be difficult to detect during routine visual inspection. UCIPM (2008) states that the eggs are best seen with the use of a hand lens.
  
• 
  In contrast, nymphs and adults of B. cockerelli are 2 mm and 3 mm in length respectively and are likely to be detected with the naked eye (Horticulture New Zealand 2009).
  
• 
  Furthermore, feeding psyllids excrete visible waxy beads of excess sugar (Clark 2005).
  

• 
  Existing pest management procedures applied in some countries may reduce the likelihood of ‘Ca. L. psyllaurous’ infected psyllids entering Australia.
  
• 
  In New Zealand, a voluntary code of practice is used for the management of the tomato/potato psyllid in greenhouse tomato and capsicum crops (NZCOP 2008). This code of practice includes both pre-harvest measures and post-harvest measures. The pre-harvest measures include management of alternative hosts, increased hygiene in and around the greenhouses, crop removal, cleaning greenhouses between crops, monitoring for the tomato/potato psyllid and insecticide applications. Post-harvest measures include keeping packaging areas clean, washing or brushing and packing export fruit in line with standard grading procedures, inspection and air blasting where necessary for truss tomatoes and fruit with calyces and segregating export fruit. However, not all host commodities are produced according to this code of practice and these measures are not mandatory. The New Zealand code of practice is in Appendix B.
  
• 
  Bactericera cockerelli nymphs use their piercing mouth parts to extract plant juices from foliage. Therefore, in the case of nursery stock containing foliage, this species has the potential to remain active during transport and storage, and may be able to develop from nymphs to breeding adults.
  
• 
  Bactericera cockerelli can survive as nymphs for up to 90 days but usually takes only 14–21 days before developing into adults. Eggs hatch within a few days of being laid. The entire duration of the lifecycle is 4–5 weeks, but this varies considerably depending on hosts and temperature (UNL 2009).
  
• 
  Nursery stock is expected to be shipped at moderate temperatures and humidity levels, which are unlikely to adversely affect any ‘Ca. L. psyllaurous’ infected psyllids populations that are present during shipment.
  
• 
  The optimum temperature for the development and survival of B. cockerelli is 27°C. Temperatures below 16°C or above 32°C are reported to adversely affect the development and survival of this pest (Ferguson et al. 2003).
  
• 
  However, fresh fruit is expected to be subject to cool temperatures during storage and transport. The storage temperatures for tomato fruit is 9–13°C (PeakFresh 2008).
  
• 
  These storage temperatures are not lethal to B. cockerelli, but will slow down the egg laying and hatching processes. It is unknown, but considered unlikely, that these temperatures would reduce or eliminate ‘Ca. L. psyllaurous’ within the psyllid.
  
• 
  Tomatoes are also highly perishable so short transport periods are necessary. Transport of fruit to Australia by either air or sea freight takes from few hours to one week (Agribusiness Information Centre 2009). The short time from field to market also suggests that there would be little or no impact on the survival of ‘Ca. L. psyllaurous’ within the eggs, nymphs or adults of B. cockerelli during post-harvest transport and storage.
  
• 
  Nymphs and adults may enter through consignments of host fruit, such as capsicum and tomato. Capsicums and truss tomatoes may be particularly suitable for the importation of B. cockerelli, due to the presence of the calyx and the recesses between the calyx and the fruit where nymphs and adults may lodge.
  
  Draft PRA report for ‘Candidatus Liberibacter psyllaurous’ Risk assessments for pathways
  

The likelihood that ‘Ca. L. psyllaurous’, having entered Australia in an infected psyllid will be transferred in a viable state to a host plant has been determined to be HIGH.

• 
  Bactericera cockerelli infected with ‘Ca. L. psyllaurous’ imported into Australia on fruit and nursery stock of host plants would be distributed within Australia through wholesale and retail sale for consumption or growth in commercial production areas.
  
• 
  The bacterium is associated with all life stages of B. cockerelli, including eggs (Hansen et al. 2008). Fruit or nursery stock could be infested with eggs, nymphs or adults of the psyllid. Eggs hatch in 5–9 days and nymphal development takes 19–24 days, depending on the temperature (Abdullah 2008).
  
• 
  For infected psyllids to transfer to host plants they would need to complete their development into adults so that they can fly to the host plant. However, immature stages of the psyllid must have suitable food sources to allow them to survive until they mature. Due to the relatively long developmental time (up to 30 days from egg to adult), there is likely to be some mortality of eggs and nymphs.
  
• 
  Bactericera cockerelli has a wide host range, feeding on plants in the Solanaceae, Convolvulaceae and Lamiaceae (Appendix A). Hosts of the psyllid are widely distributed in Australia. These hosts include the common weeds silverleaf nightshade (Datura stramonium), fierce thorn-apple (Datura ferox), sacred datura (Datura inoxia) and jimson-weed (Datura metel and Datura stramonium).
  
• 
  ‘Candidatus L. psyllaurous’ has a narrower host range than B. cockerelli. Its known hosts are cape gooseberry, capsicum, chilli, potato, tamarillo and tomato (MAFBNZ 2008). These plants are grown widely in home gardens and commercial vegetable growing areas.
  
• 
  Australia has a diverse flora of the Solanaceae (23 genera and about 200 species) but the susceptibility of these species to ‘Ca. L. psyllaurous’ is unknown.
  
• 
  As ‘Ca. L. psyllaurous’ is a newly described pathogen, it is likely further hosts will be identified.
  
• 
  For ‘Ca. L. psyllaurous’ to be transferred from fruit to a suitable host, infected psyllids would need to find a host of the bacterium, feed, and successfully transmit the bacterium to the host.
  
• 
  Imported nursery stock is likely to be planted directly into suitable habitats to grow. If infected psyllids are imported on a ‘Ca. L. psyllaurous’ host, there is no requirement for the psyllid to be transported to a suitable host. Infected nymphs would be able to transmit ‘Ca. L. psyllaurous’ to the imported host plant and thus distribute the bacterium.
  
• 
  If infected psyllids are imported with nursery stock of a non-‘Ca. L. psyllaurous’ host, the psyllid would need to move from the pathway to a suitable host.
  

• 
  Psyllids can migrate long distances and flights of up to 83 km have been recorded (HTWG 2007). Similar long flights are likely to be undertaken by B. cockerelli.
  
• 
  Nymphs are also capable of crawling short distances. However, nymphs typically settle on the undersides of leaves to feed (Horticulture New Zealand 2009), and would therefore be a lower risk for movement.
  
• 
  In the case of plant material for commercial use, if infested nursery stock was introduced, the psyllid could potentially move to other suitable host plants surrounding them, and be passively redistributed by the further movement of these infested plants.
  
• 
  For infected psyllids imported as eggs to transfer to a ‘Ca. L. psyllaurous’ host plant, they would need to complete their development into adults so that they can fly to the host plant.
  
• 
  Infected eggs hatch in 5–9 days and nymphal development takes 19–24 days, depending on the temperature (Abdullah 2008). However, immature stages of the psyllid must have suitable food sources to survive until they mature. Due to the relatively long developmental time (up to 30 days from egg to adult), there is likely to be some mortality of eggs and nymphs.
  
• 
  Although the intended use of imported fresh fruit is human consumption, waste material would be generated (e.g. overripe and damaged fruit, uneaten portions).
  
• 
  Whole or parts of the imported fruit may be disposed of at multiple locations throughout Australia in compost bins or amongst general household waste. Adults may be able survive on waste material for a short time before dispersing to suitable hosts.
  

5.1.5 Overall probability of entry

Table 5.1: Overall probability of entry of ‘Ca. L. psyllaurous’ for pathways

5.2 Probability of establishment

The likelihood that ‘C. L. psyllaurous’ will establish within Australia, based on a comparison of factors in the source and destination areas considered pertinent to its survival and reproduction, is HIGH.

• 
  ‘Candidatus L. psyllaurous’ occurs in North Dakota, Texas, New York, Colorado, Kansas, New Mexico, Utah, Idaho, Arizona, Wyoming, Nebraska and California in the USA; Alberta in Canada; Satillo in Mexico; and New Zealand (Carter 1939; MAFBNZ 2008).
  
• 
  The climatic regions across this range are diverse and include desert, steppe, Mediterranean, marine west coast, humid continental and humid subtropical (Espenshade 1990).
  
• 
  There are similar climatic regions in parts of Australia that would be suitable for the establishment of the bacterium.
  
• 
  The entry of ‘Ca. L. psyllaurous’ in imported nursery stock would allow the establishment of the bacterium in plants produced from this material.
  
• 
  There are no agri-chemicals available for control of ‘Ca. L. psyllaurous’ (Horticulture New Zealand 2008) and any chemicals used on host plants in Australia are not expected to prevent the bacterium establishing in a host plant.
  
• 
  A number of hosts of ‘Ca. L. psyllaurous’ are perennial. If a perennial host, such as tamarillo, was infected the bacterium would be able to establish a persistent population.
  
• 
  If potato plants were infected, ‘Ca. L. psyllaurous’ could establish in the plants and be passed on to daughter plants through tubers (Shapovalov 1929).
  
• 
  If annual hosts such as capsicum, chilli and tomato were infected, the bacterium would only be established in the plants until they died at the end of the season.
  
• 
  Should ‘Ca. L. psyllaurous’ enter Australia in B. cockerelli, the psyllid could form a founding population. However, this would rely on sufficient numbers of adult psyllids being released into the Australian environment. A founding population of the psyllid would be able to transmit ‘Ca. L. psyllaurous’ to other host plants and create a founding population of the bacterium.
  
• 
  Australian climatic conditions in the commercial horticultural growing areas would support the development and survival of B. cockerelli.
  
• 
  It is not certain how ‘Ca. L. psyllaurous’ entered and established in New Zealand, but the presence of the tomato-potato psyllid in New Zealand only two years prior to the confirmation of ‘Ca. L. psyllaurous’ in New Zealand suggests that it was introduced with the psyllid and was able to establish an undetected founding population (MAFBNZ 2008).
  

The ability of ‘Ca. L. psyllaurous’ to multiply in infected hosts, especially in perennial species imported as nursery stock, supports a likelihood of ‘high’ for the establishment of ‘Ca. L. psyllaurous’ in Australia.

5.3 Probability of spread

• 
  The spread of ‘Ca. L. psyllaurous’ within Australia would rely on the movement of infected potato tubers, nursery stock or B. cockerelli.
  
• 
  There is the potential for the spread of the bacterium directly through infected potato tubers but premature sprouting and the production of spindly sprouts by infected tubers (UNL 2009) may limit this spread as these tubers are unlikely to be planted or produce daughter plants.
  
• 
  ‘Candidatus L. psyllaurous’ could be spread to new areas through the movement of infected planting material. As visual symptoms may not be present, and in the absence of specific testing regimes, infected nursery stock could easily be moved to new areas.
  
• 
  Existing interstate quarantine control measures on the movement of nursery stock and potato tubers could reduce the rate of spread of ‘Ca. L. psyllaurous’.
  
• 
  If ‘Ca. L. psyllaurous’ entered in infected B. cockerelli and the psyllid established in Australia, the bacterium would be spread into new areas by the psyllid (Kumarasinghe 2008).
  
• 
  Bactericera cockerelli has been reported from a variety of areas and environments. Its distribution includes Minnesota, North Dakota, South Dakota, Nebraska, Kansas, Oklahoma, Texas and all states for Oregon and Washington. It was detected in Canada in Alberta and Saskatchewan. It is also reported from as far south as Mexico City and Rio Frio, Puebla (Cranshaw 1993). It has recently been detected in the Auckland region of New Zealand, both in greenhouse tomato and capsicum nurseries and commercial potato crops (MAFBNZ 2008). There are similarities in the natural and managed environment of these regions with many areas of Australia. This suggests that many areas in Australia where hosts of ‘Ca. L. psyllaurous’ are grown would be suitable for the spread of the bacterium by B. cockerelli.
  
• 
  ‘Candidatus L. psyllaurous’ is wide spread in the potato, tomato, capsicum and eggplant growing areas of New Zealand (MAFBNZ 2008). This demonstrates the ability of the bacterium to spread if its vector and hosts are present.
  
• 
  It is unlikely any of the endemic species of psyllid in Australia would be able to vector the bacterium. ‘Candidatus L. psyllaurous’ is only known to be vectored by B. cockerelli and the only species of Australian Psyllidae or Triozidae known to feed on a solanaceous host is an undescribed species of Acizzia found on eggplant (Kent 2008).
  
• 
  The widespread distribution of hosts of ‘Ca. L. psyllaurous’ and B. cockerelli in many regions of Australia would assist the spread of ‘Ca. L. psyllaurous’ if the pathogen and its vector were established in Australia.
  
  Draft PRA report for ‘Candidatus Liberibacter psyllaurous’ Risk assessments for pathways
  
• 
  Psyllids can migrate long distances and flights of up to 83 km have been recorded (HTWG 2007). Adult B. cockerelli are strong fliers and can also be blown on the wind (Horticulture New Zealand 2008).
  
• 
  The bacterium is not spread mechanically by rubbing or handling or on machinery or clothing during production of crops (Horticulture New Zealand 2008).
  

5.4 Overall probability of entry, establishment and spread

The overall likelihood that ‘Ca. L. psyllaurous’ will enter Australia by the pathways discussed in this PRA, be distributed in a viable state to susceptible hosts, establish in that area and subsequently spread within Australia are set out in Table 5.2.

Table: 5.2: Overall probability of entry, establishment and spread of ‘Ca. L. psyllaurous’ for pathways

Pathway	Probability of entry	Probability of establishment	Probability of spread	Overall probability of entry, establishment and spread
Fruit (including seed)	Extremely low	High	High	Extremely low
Tubers	Moderate			Moderate
Nursery stock	High			High
Infected psyllids	High			High

5.5 Consequences

Based on the decision rules described in Table 2.4, that is, where the consequences of a pest with respect to a single criterion has an impact of ‘F’, the overall consequences are estimated to be High.

5.6 Unrestricted risk

5.7 Risk assessment conclusion

The unrestricted risk for ‘Ca. L. psyllaurous’ for the fruit pathway has been assessed as ‘very low’, which meets Australia’s ALOP. Therefore, specific risk management measures for fruit are not required.

The unrestricted risk for ‘Ca. L. psyllaurous’ for the potato tuber, nursery stock and infected tomato-potato psyllid pathways has been assessed as ‘high’, which is above Australia’s ALOP. Therefore, specific risk management measures are required to ensure that the bacterium does not enter, establish and spread though these pathways.

Table 5.3: Summary of pathway risk assessments for ‘Candidatus L. psyllaurous’