Draft report for the non-regulated analysis of existing policy for fresh strawberry fruit from the Republic of Korea
Assessments for quarantine pests for which a full pest risk assessment is conducted
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Assessments for quarantine pests for which a full pest risk assessment is conducted4.1Angular leaf spotXanthomonas fragariaeAngular leaf spot is a disease of strawberries caused by a gram-negative bacterium Xanthomonas fragariae (Parkinson et al. 2007). Xanthomonas fragariae was first detected in Minnesota, USA in 1960 (Kennedy & King 1962a) and has since become an important pest of strawberries in the United States. Natural hosts of this bacterium appear to be limited to strawberries. Experimental data indicate susceptibility to X. fragariae varies among different strawberry cultivars (Bestfleisch et al. 2015; Maas et al. 2000), with fully resistant genotypes not yet identified. In Australia X. fragariae has been found in Gosford in 1975, Adelaide Hills in 1994 and Bundaberg in 2010. These outbreaks have since been eradicated and Australia is now considered to be free from X. fragariae (Australian Government Department of Agriculture 2012; EPPO 1996; Gillings, Fahy & Bradley 1998; McGechan & Fahy 1976; Young et al. 2011).
Infection of strawberry leaves occurs through the stomata. Under optimal conditions or once the infection has become systemic, the calyx may become infected with symptoms identical to those of leaves (Heidenreich & Turechek 2016; Peres 2014). Under favourable conditions the lesions on the calyx and flowers can secrete bacteria in the form of viscous droplets (Gubler et al. 1999; Peres 2014). In the crown, water-soaked lesions may be localised or confined to one section (Hildebrand, Schroth & Wilhelm 1967). In addition to host specificity, many Xanthomonas species and pathovars show tissue specificity as well, invading either intercellular spaces of mesophyll tissue (mesophylic pathogens) and/or xylem elements of vascular tissue (vascular pathogens) (Ryan et al. 2011). Hildebrand, Schroth and Wilhelm (1967) reported that X. fragariae is a vascular pathogen, being found in both cambium and xylem tissue. The spread of X. fragariae occurs through infected propagative material, overhead irrigation, rain splash and windblown droplets (Hildebrand, Schroth & Wilhelm 1967). Seed transmission has not been demonstrated. Outbreaks of this disease in California are associated with rainfall or overhead irrigation, with higher levels of infection in nurseries planted in spring (Hildebrand, Schroth & Wilhelm 1967). The risk scenario of concern for X. fragariae is that symptomless infected strawberry fruit may be imported into Australia.
4.1.1Likelihood of entryThe likelihood of entry is considered in two parts, the likelihood of importation and the likelihood of distribution, which consider pre-border and post-border issues, respectively. Likelihood of importationThe likelihood that Xanthomonas fragariae will arrive in Australia with the importation of strawberries from Korea is: Moderate. The following information provides supporting evidence for this assessment. Fragaria spp. and Fragaria × ananassa are highly susceptible to angular leaf spot caused by Xanthomonas fragariae (Bestfleisch et al. 2015; Maas et al. 2000; Stöger et al. 2008). Xanthomonas fragariae has been reported present in Sugok-myon, Jinju city, Okjong-myon, Hadong-gun in Gyeongsangnam-do province (Kwon et al. 2010). Gyeongsangnam-do province is one of the major strawberry producing areas accounting for 34 per cent of total strawberry production (QIA 2015b). Angular leaf spot has been reported on strawberries in Korea in both open field farms and greenhouses (Kwon et al. 2010). Korea currently tests for the presence of X. fragariae in imported runner daughter plants (QIA 2015b). However no testing for this pathogen takes place during production process for certified plantlets. Plantlets with obvious symptoms of infection are likely to be removed during the multiplication process. Some infected plantlets may exhibit no or mild symptoms and may be used during the multiplication process. Infected plants can remain asymptomatic until optimum conditions for the disease to develop are present (Louws, Harrison & Garrett 2014; Mahuku & Goodwin 1997; NPPO the Netherlands 2013; Roberts et al. 1996; Wang & Turechek 2016). Transmission of this bacterium can occur over a short distance via rain/water splash (Hildebrand, Schroth & Wilhelm 1967; Roberts, Jones & Chandler 1997). Greenhouse production is not exposed to rainfall and overhead irrigation is not used, which would limit the spread of the bacterium, if present.
Strawberries with obvious symptoms of infection in the calyx are likely to be removed during harvesting and packing procedures and would not be packed for export. Strawberries that are asymptomatic or with only mild symptoms on the calyx could escape detection during packing procedures and be exported. Strawberries are usually stored and transported at low temperatures to prolong shelf life. Xanthomonas fragariae is slow growing and can survive cold storage in host tissue up to one year (Hildebrand, Schroth & Wilhelm 1967; Louws, Harrison & Garrett 2014). Some infected fruit may exhibit no or mild symptoms at the time they arrive in Australia.
Likelihood of distributionThe likelihood that Xanthomonas fragariae will be distributed within Australia in a viable state as a result of the processing, sale or disposal of strawberry fruit from Korea and subsequently transfer to a susceptible part of a host is: Low. The following information provides supporting evidence for this assessment. Imported strawberries are intended for human consumption. Distribution would be for retail sale and likely to be Australia wide. As strawberries will be packaged in punnets, packed strawberries may not be processed or handled again until they arrive at retailers. Therefore, the bacterium, if present in packed strawberries, is unlikely to be detected during transportation and distribution to retailers. Strawberries with obvious symptoms of infection would not be marketable and would not be sold. Strawberries without symptoms, or with only minor symptoms, could be marketable and sold. Most fruit waste will be discarded into managed waste systems and will be disposed of in municipal tips and would therefore pose little risk of exposure to a suitable host. Consumers will discard small quantities of fruit waste in urban, rural and natural localities. Small amounts of fruit waste will be discarded in domestic compost. There is some potential for consumer waste being discarded near host plants (strawberry plants), including commercially grown, household or wild host plants. If present in fruit waste, the bacterium would then need to be transferred to the host plants.
Generally survival of a pathogen in fruit waste is expected to be short due to dehydration and competition with other organisms. However, based on the above studies regarding the survival of this bacteria in soil on tissue and dried leaves, it is possible that the bacterium could survive in fruit waste for a longer period of time increasing the chances of the bacterium coming into contact with the host plants. To date, strawberries are the only confirmed natural hosts of X. fragariae (Kennedy 1965; NPPO the Netherlands 2013). In Australia strawberries are grown in all states commercially and are also grown as a garden plant in household (ABS 2016). Strawberries are infrequently encountered as a weed in Australia (CHAH 2016; Groves 2002). There are reports of naturalised Fragaria vesca in localised areas in New South Wales and Queensland and Fragaria × ananassa in localised areas in South Australia (CHAH 2016; Groves 2002). Kennedy (1965) reported that under experimental conditions species in the genus Potentilla can become infected by X. fragariae. Species in the genus Potentilla can be found distributed throughout Australia (CHAH 2016). However, there have been no reports of infection of Potentilla under natural conditions in the field. On host plants the bacterium can be transmitted over short distances via water splash approximately three metres, possibly further under extreme weather conditions (Roberts, Jones & Chandler 1997). Any bacteria splashed onto a non-host or soil is expected to not survive for long. To date, there have been no vectors identified for this bacterium. Transmission of X. fragariae through seeds is suspected to be possible (Mark Herrington [Queensland Department of Agriculture and Fisheries] 2016 pers. comm., 20 May). However, there is no evidence to confirm seed transmission of this bacterium yet. Strawberry seeds (achenes) may germinate producing plants. However, most seeds are dormant and will not germinate without scarification (Galvão et al. 2014). Scarification may include heat treatment, cutting the seed or the use of chemicals (El Hamdouni 2001; Guttridge & Bright 1978; Ito et al. 2011; Miller et al. 1992; Nakamura 1972; Thompson 1968; Wilson, Goodall & Reeves 1973). These treatments are unlikely to be met outside of commercial situations. Due to this reason, germination of strawberry seed from fruit waste is considered unlikely. Imported strawberries are intended for human consumption and would likely be distributed Australia wide. Strawberries will be packaged in punnets and may not be processed or handled again until they arrive at retailers. Small quantities of fruit waste could be discarded in urban, rural and natural localities. Xanthomonas fragariae can potentially survive for a long period of time on infested fruit waste. Natural hosts of X. fragariae are limited to plants of the genus Fragaria. This bacterium is transmitted via water splash which limits its potential for dispersal to short distances and no vectors have been identified. Although the possibility of this bacterium being transmitted through seed is suspected, seed transmission is not confirmed. Strawberry seeds are unlikely to germinate without treatment. This information supports a likelihood estimate for distribution of ‘low’.
Overall likelihood of entryThe overall likelihood of entry is determined by combining the likelihood of importation with the likelihood of distribution using the matrix of rules shown in Table 2.2. The likelihood that Xanthomonas fragariae will enter Australia as a result of trade in strawberry fruit from Korea and be distributed in a viable state to a susceptible host is: Low. 4.1.2Likelihood of establishmentThe likelihood that Xanthomonas fragariae will establish within Australia based on a comparison of factors in the source and destination areas that affect pest survival and reproduction is: High. The following information provides supporting evidence for this assessment. Strawberries, the natural host for X. fragariae, are widely grown commercially and domestically across Australia. Plants in the genus Fragaria are highly susceptible to X. fragariae (Bestfleisch et al. 2015; Maas et al. 2000).
Preferred environmental conditions for bacterial development are warm days around 20 °C and cold nights at 2 °C (Kennedy-Fisher 1997; Kennedy & King 1962b; Naqvi 2004; Peres 2014). High humidity levels affect disease development (Hildebrand et al. 2005; Kennedy & King 1962b) with rain and overhead irrigation increasing the chances of disease outbreak (Epstein 1966; Hildebrand, Schroth & Wilhelm 1967). These climate conditions can be found in some strawberry production regions of Australia. In some areas overhead irrigation may also be used to protect strawberries from frost damage, increasing the likelihood of establishment in those areas (DAFWA 2015; Naqvi 2004; Nicholls et al. 2008). Korean strawberries are expected to be exported between January and March, during Australia’s summer. Average temperatures in Australia during this period range from 12 °C to 36 °C (Bureau of Meteorology 2016). High temperatures above 28 °C are unfavourable for the expression of angular leaf spot and may reduce the potential for the bacterium to infect the host plants (Kennedy & King 1962a). However, Roberts et al. (1996) reported that bacteria are likely to survive higher temperatures, remaining asymptomatic in the plant material until optimum conditions are available. Strawberries are infrequently encountered outside managed cultivation in Australia (CHAH 2016; Groves 2002). There are reports of naturalised Fragaria vesca in localised areas in New South Wales and Queensland and Fragaria × ananassa in localised areas in South Australia (CHAH 2016; Groves 2002). These plants may become infected becoming a source of inoculum for the bacterium. The localised and infrequent distribution of these plants will limit them as a source of inoculum for infection. Previous outbreaks of X. fragariae occurred in Gosford in 1975, in Adelaide Hills in 1994 and in Bundaberg in 2010 (Gillings, Fahy & Bradley 1998; McGechan & Fahy 1976; Young et al. 2011) indicating that suitable environmental conditions for X. fragariae exist in Australia. Currently X. fragariae is known to be established in multiple countries over a variety of climatic zones including Argentina, Brazil, Canada, Ethiopia, France, Germany, Italy, Korea, Paraguay, Taiwan, United States, Uruguay and Venezuela (CABI & EPPO 1997b; NPPO the Netherlands 2013). Environments with climate conditions similar to these regions exist in various parts of Australia, suggesting X. fragariae has the potential to establish in Australia. Transmission of X. fragariae through seeds is suspected to be possible (Mark Herrington [Queensland Department of Agriculture and Fisheries] 2016 pers. comm., 20 May). However, there is no evidence to confirm seed transmission of this bacterium yet. Plants in the genus Fragaria are highly susceptible to X. fragariae. Xanthomonas fragariae is able to survive long periods of time in adverse conditions. Environmental conditions suitable for the development of angular leaf spot can be found in some strawberry growing areas of Australia. Outbreaks of X. fragariae previously occurred in Australia. This information supports a likelihood estimate for establishment of ‘high’. 4.1.3Likelihood of spreadThe likelihood that Xanthomonas fragariae will spread within Australia, based on a comparison of factors in the source and destination areas that affect the expansion of the geographic distribution of the pest is: Moderate. The following information provides supporting evidence for this assessment. Xanthomonas fragariae can be transmitted via infected tools, machinery and humans who come in contact with the bacterium (Naqvi 2004). Xanthomonas fragariae can be dispersed over short distances, approximately three metres, via water splash, including rain and water which has touched the surface of infected tissues including overhead sprinkler irrigation. Dispersal distance could be further under extreme weather conditions (Roberts, Jones & Chandler 1997). Xanthomonas fragariae can be transmitted through infected plants introduced to a field (Peres 2014). Infected nursery stock can be symptomless retaining the inoculum to spread to other host plants (Mahuku & Goodwin 1997). Long distance dispersal of X. fragariae is more likely to be through the movement of infected strawberry planting material (runners). However, strawberry planting material certified as being free of pests and pathogens is available from the Queensland Strawberry Runner Accreditation Scheme and the Victorian Certified Runner Scheme (DAFWA 2016; Strawberries Australia 2016; Strawberries Australia Inc 2012). The Victorian Certified Runner Scheme produces 75 per cent of Australian strawberry runners used in national fruit production (Victorian Strawberry Industry Certification Authority 2010), making this pathway for spread less likely. Natural hosts of X. fragariae are limited to plants in the genus Fragariae. Strawberries are grown commercially and domestically in all states of Australia and can be grown domestically in the ACT and NT (ABS 2016). Fragaria vesca and Fragaria × ananassa can be infrequently encountered in unmanaged environment of Australia (CHAH 2016; Groves 2002).
To date, there have been no vectors identified for this bacterium. Xanthomonas fragariae can be transmitted via infected tools, machinery and humans who come in contact with the bacterium. Xanthomonas fragariae can only be transmitted over short distances via water splash. Long distance dispersal of this bacterium could occur through the movement of infected strawberry planting material. However, strawberry planting material is certified as being free of pests and pathogens from Queensland Strawberry Runner Accreditation Scheme and the Victorian Certified Runner Scheme, making this mode of spread less likely. This information supports a likelihood estimate for spread of ‘moderate’. 4.1.4Overall likelihood of entry, establishment and spreadThe overall likelihood of entry, establishment and spread is determined by combining the likelihoods of entry, of establishment and of spread using the matrix of rules shown in Table 2.2. The overall likelihood that Xanthomonas fragariae will enter Australia as a result of trade in strawberry fruit from Korea, be distributed in a viable state to a susceptible host, establish in Australia and subsequently spread within Australia is: Low. 4.1.5ConsequencesThe potential consequences of the establishment of Xanthomonas fragariae in Australia have been estimated according to the methods described in Table 2.3. Based on the decision rules described in Table 2.4, that is, where the potential consequences of a pest with respect to one or more criteria are ‘E’, the overall consequences are estimated to be Moderate.
4.1.6Unrestricted risk estimateUnrestricted risk is the result of combining the likelihoods of entry, establishment and spread with the outcome of overall consequences. Likelihoods and consequences are combined using the risk estimation matrix shown in Table 2.5.
As indicated, the unrestricted risk estimate for Xanthomonas fragariae has been assessed as ‘low’, which does not achieve the ALOP for Australia. Therefore, specific risk management measures are required for this pest. Assessments for quarantine pests for which the URE outcome is adopted from previous assessments4.2ThripsFrankliniella intonsa (EP) and Frankliniella occidentalis (EP, NT)Frankliniella intonsa (Eurasian flower thrips) and F. occidentalis (western flower thrips) have been grouped together because of their related biology and taxonomy, and they are predicted to pose a similar risk and to require similar mitigation measures. Frankliniella occidentalis is not present in the Northern Territory and is a pest of quarantine concern for that territory. Frankliniella intonsa is not present in any part of Australia and is therefore a pest of quarantine concern for the whole of Australia. Both thrips species were assessed previously in a number of existing import policies, for example, in the import policy for capsicums from Korea (Biosecurity Australia 2009a), unshu mandarins from Japan (Biosecurity Australia 2009b), and stone fruit from the United States (Biosecurity Australia 2010b). Frankliniella occidentalis was also included in the import policy for table grapes from China (Biosecurity Australia 2011a), Japan (Australian Department of Agriculture 2014) and Korea (Biosecurity Australia 2011b), as well as several other existing policies. In these policies, the unrestricted risk estimates for thrips were all assessed as exceeding the ALOP for Australia. Therefore, specific risk management measures are required for thrips. The department considered factors affecting the likelihood of importation for thrips for strawberries from Korea and those previously assessed. The department considers that the likelihood of importation for thrips for strawberries from Korea would be comparable to that in the previous assessments. Thrips have a wide host range and host material is likely to be available all year round in Australia. The likelihood of distribution for these pests for strawberries from Korea would be comparable to that for commodities assessed previously. The likelihood of establishment and spread of F. intonsa in Australia and F. occidentalis in the Northern Territory for strawberries from Korea will be comparable to previous assessments. These likelihoods relate specifically to events that occur in Australia and are principally independent of the importation pathway. The consequences of F. intonsa in Australia and F. occidentalis in the Northern Territory are principally independent of the importation pathway. In addition, the department has also reviewed the latest literature and no new information is available that would significantly change the risk ratings for importation, distribution, establishment, spread and consequences as set out for thrips in existing policies. 4.2.1Unrestricted risk estimateThe unrestricted risk estimate for thrips for strawberries from Korea is comparable to the estimates in previous assessments, and does not achieve the ALOP for Australia. Therefore, specific risk management measures are required for these pests. Assessments for quarantine pests for which some of the likelihood and/or consequence ratings are adopted from previous assessments4.3Kanzawa spider miteTetranychus kanzawai (EP, WA)Tetranychus kanzawai is not present in the state of Western Australia and is a pest of quarantine concern for that state. Tetranychus kanzawai is a spider mite native to East Asia. It is referred to as a ‘spider mite’ due to its habit of spinning silken webs on plants, within which they seek shelter from predators and unfavourable environmental conditions (Yano 2012; Oku et al 2009). Adults are small in size; females grow to between 0.3 and 0.5 millimetres long (Zhang 2008) and males are typically smaller. Tetranychus kanzawai is highly polyphagous as a species, feeding on plants such as pear, tea, hydrangea, as well as strawberry, but exhibits strong intraspecific differences, and different populations have been shown to have different food preferences, responses in temperature, even reproductive incompatibility (Gomi & Gotoh 1996; Hinomoto & Takafuji 2011; Takafuji, Santoso & Hinomoto 2001). Whilst some populations were shown not to be capable of completing their lifecycle on certain plants, all known populations are capable of completing their lifecycle on strawberry plants (Gomi & Gotoh 1996). Tetranychus kanzawai has in total five stages of life—egg, larva, protonymph, deutonymph, and adult (CABI 2016). Their short lifecycle means that they go through many generations in a year (Gotoh & Gomi 2000). All spider mites feed by piercing plant cells and consuming their contents (Zhang 2008). Leaves damaged by Tetranychus develop yellowish/brownish spots due to the removal of moisture by feeding and large numbers may result in stunted growth of plants, reduced fruit quality, and eventually plant death (Alford 2007; CABI 2016; Zhang 2008). Strawberry plants have been recorded as a viable host of T. kanzawai (Gomi & Gotoh 1996; Zhang et al. 1996b). Tetranychus kanzawai can survive in a wide range of temperatures. In a study of its growth performance at different temperatures (Ullah et al. 2011), it was found to be able to reach maturity at constant temperatures of 15 °C up to a temperature of 37.5 °C. The fastest development time from newly laid egg to adult was found at 35 °C, at an average of 5.3 days for females and 5.1 days for males with a period of less than a day before adults started laying eggs (Ullah et al. 2011). The slowest development time was found at 15 °C, at 24.5 days for females and 24.4 days for males (Ullah et al. 2011). At a constant temperature of 40 °C, some T. kanzawai eggs hatched, but none of the larvae reached adulthood (Ullah et al. 2011). Yang et al (1991) found in their study that 22 per cent of T. kanzawai adults could survive temperatures as low as –5 °C for ten days, but on the other hand, Ullah et al (2011) reported that development stopped and the lowest temperature at which a population can reproduce was likely closer to 10 °C. The differences may be dependent on the population it came from (Takafuji, Santoso & Hinomoto 2001). The risk scenario of concern is that T. kanzawai adults and larvae are present on harvested strawberry fruit and brought to Australia. Tetranychus kanzawai was included in the existing import policy for table grapes from Japan (Australian Department of Agriculture 2014), Korea (Biosecurity Australia 2011b), and China (Biosecurity Australia 2011a). The assessment of T. kanzawai presented here builds on these existing policies. Tetranychus kanzawai has a wide host range and host material is likely to be available all year round in Australia. In addition, after importation strawberries will be distributed throughout Australia for retail sale in a similar way to table grapes assessed previously. Therefore, the likelihood of distribution for this pest for strawberries from Korea would be comparable to that assessed previously. The likelihood of establishment and spread of T. kanzawai in Western Australia for strawberries from Korea will be comparable to previous assessments. These likelihoods relate specifically to events that occur in Australia and are principally independent of the importation pathway. The consequences of T. kanzawai in Western Australia are also principally independent of the importation pathway. In addition, the department has also reviewed the latest literature and no new information is available that would significantly change the risk ratings for distribution, establishment, spread and consequences as set out for T. kanzawai in the existing policies. However, differences in climatic conditions, the commodity, pest prevalence and commercial production practices between previous exporting areas and Korea make it necessary to reassess the likelihood of importation of T. kanzawai into WA with strawberries from Korea. 4.3.1Likelihood of entryThe likelihood of entry is considered in two parts, the likelihood of importation and the likelihood of distribution, which consider pre-border and post-border issues, respectively. Likelihood of importationThe likelihood that Tetranychus kanzawai will arrive in Australia with the importation of strawberries from Korea is: Moderate. The following information provides supporting evidence for this assessment. Tetranychus kanzawai is known to be a pest of strawberries in Korea (QIA 2015b) and is known to be capable of completing its lifecycle on strawberry plants (Gomi & Gotoh 1996; Zhang et al. 1996a). Whilst Tetranychus mites feed mainly on leaves, they may be found on fruit during high infestation levels (NAPPO 2014). High infestation levels of T. kanzawai leads to noticeable direct damage to the plant as well as silk webbing on the areas infested (Zhang 2008). There is also comparatively small space for T. kanzawai to hide on strawberry fruit when compared to grape bunches, and strawberries are picked and packed individually. Therefore, more heavily infested fruit is likely to be detected and removed during standard commercial quality processes.
Likelihood of distributionThe likelihood that Tetranychus kanzawai will be distributed within Australia in a viable state as a result of the processing, sale or disposal of strawberry fruit from Korea and subsequently transfer to a susceptible part of a host assessed here would be similar for table grapes from China (Biosecurity Australia 2011a) and table grapes from Korea (Biosecurity Australia 2011b), that is: Moderate. Overall likelihood of entryThe overall likelihood of entry is determined by combining the likelihood of importation with the likelihood of distribution using the matrix of rules shown in Table 2.2. The likelihood that Tetranychus kanzawai will enter Australia as a result of trade in strawberries from Korea and be distributed in a viable state to a susceptible host is: Low. 4.3.2Likelihood of establishment and spreadAs indicated, the likelihood of establishment and of spread for Tetranychus kanzawai is being based on the assessment for table grapes from China (Biosecurity Australia 2011a), and table grapes from Korea (Biosecurity Australia 2011b). The ratings from the previous assessments are: Likelihood of establishment High Likelihood of spread Moderate 4.3.3Overall likelihood of entry, establishment and spreadThe overall likelihood of entry, establishment and spread is determined by combining the likelihoods of entry, of establishment and of spread using the matrix of rules shown in Table 2.2. The overall likelihood that Tetranychus kanzawai will enter Australia as a result of trade in strawberries from Korea, be distributed in a viable state to a susceptible host, establish in Australia and subsequently spread within Australia is: Low. 4.3.4ConsequencesAs indicated, consequences of T. kanzawai in Western Australia assessed here are based on the previous assessment for T. kanzawai for table grapes from China (Biosecurity Australia 2011a), which was adopted for table grapes from Korea (Biosecurity Australia 2011b) and Japan (Australian Department of Agriculture 2014), that is Moderate. 4.3.5Unrestricted risk estimateUnrestricted risk is the result of combining the likelihoods of entry, establishment and spread with the outcome of overall consequences. Likelihoods and consequences are combined using the risk estimation matrix shown in Table 2.5.
As indicated, the unrestricted risk estimate for Tetranychus kanzawai has been assessed as ‘low’, which does not achieve the ALOP for Australia. Therefore, specific risk management measures are required for this pest. 4.4Brown rotMonilinia fructigena (EP) and Monilia polystroma (EP)Brown rot is a fungal disease of stone and pome fruit caused by a number of closely related species of the genus Monilinia. The anamorph of the fungus is the genus Monilia. The genus belongs to family Sclerotiniaceae and it can cause severe losses and damage to stonefruit (Zhu, Chen & Guo 2011). However it has also been reported on other hosts including grapes and strawberries (Byrde & Willets 1977; CABI 2016; Cline & Farr 2006). Symptoms caused by brown rot fungi in general include blossom and leaf blight, cankers on woody tissues and rotting of fruit (Byrde & Willets 1977). However, brown rot primarily infects fruit, rarely blossoms and twigs (Farr & Rossman 2016). The biology and taxonomy of Monilinia fructigena and Monilia polystroma are considered sufficiently similar to justify combining them into a single assessment. The assessment of the pathogens has been largely based on the scientific information on Monilinia fructigena as it is predicted to pose a similar risk and require similar mitigation measures. Unless explicitly stated, the information presented is considered as applicable to both species. In this assessment, the common name ‘brown rot’ is used to refer to both species unless otherwise specified. The risk scenario of concern for Monilinia fructigena and Monilia polystroma is that symptomless infected fruit might enter Australia and result in the establishment of these fungi in Australia.
Differences in commodity climate conditions, pest prevalence and horticultural practices between previous export areas and Korea make it necessary to reassess the likelihood of importation of brown rot into Australia with strawberries from Korea. Brown rot fungi has multiple hosts. After importation, strawberries will be distributed throughout Australia for retail sale in a similar way to table grapes assessed previously. The likelihood of distribution for these fungi for strawberries from Korea would be comparable to that assessed previously. The likelihood of establishment and spread of brown rot fungi in Australia will be comparable to previous assessments. These likelihoods relate specifically to events that occur in Australia and are principally independent of the importation pathway. The consequences of brown rot in Australia are also principally independent of the importation pathway. In addition, the Australian Government Department of Agriculture and Water Resources has reviewed the latest literature and no new information is available that would significantly change the risk ratings for distribution, establishment, spread and consequences as set out for brown rot fungi in the existing policies.
4.4.1Likelihood of entryThe likelihood of entry is considered in two parts, the likelihood of importation and the likelihood of distribution, which consider pre-border and post-border issues, respectively. Likelihood of importationThe likelihood that Monilinia fructigena and Monilia polystroma will arrive in Australia with the importation of strawberry fruit from Korea is: Very low. The following information provides supporting evidence for this assessment. Fragaria spp. are not reported as main hosts but they are susceptible to brown rot caused by Monilinia fructigena and Monilia polystroma (CABI 2016; Kim & Koo 2009). Information on their biology on strawberry fruit has not been found. Brown rot is a pathogen favoured by moist conditions (rain, fog and other factors that increase humidity), especially at the beginning of the host’s growth periods. High light levels with warm temperatures and wet and humid conditions favour spore germination and infections (Batra 1991; Byrde & Willets 1977; CABI 2016; Jones 1990). Korea has mild springs with warm and humid summers (KMA 2011). The green house climate is controlled to replicate summer/spring conditions with day time temperatures between 20 and 25 °C. This climate is conducive to the development of brown rot and suggests that the disease, if present, is likley be detected. However, no records have been found of Monilinia fructigena or Monilia polystroma on strawberries in Korea. Brown rot fungi have the ability to cause latent infection in fruit (Gell et al. 2009). The infected fruit may not produce symptoms of disease until the fruit begins to ripen during storage and transport, on the market shelf, or as the fruit senesces (Byrde & Willets 1977). On stone fruit healthy fruit can be contaminated with conidia in the field or during processes in the packing house (Ma 2006). Wounded fruit may also be contaminated with conidia during packing house processes via fruit to fruit contact (Xu & Robinson 2000) allowing brown rot to develop during the postharvest period. It is assumed this may be possible for strawberries, increasing the chance of strawberries with no or mild symptoms to be packed for export if they are infected during the packing process. On stone fruit, brown rot fungi overwinter mainly in or on infected mummified fruit, either attached to the tree or on the ground (Byrde & Willets 1977). Mycelia can survive long periods of adverse environmental conditions within mummified fruits, twigs, cankers and other infected tissues (Byrde & Willets 1977). This suggests that in infected fruit fungi may survive cold storage and transportation processes. Brown rot fungi have the ability to cause latent infection in fruit, with symptomless infected fruit likely to pass through packing house processes undetected. Brown rot mycelia in infected fruit are likely to survive cold storage and transportation. However, strawberry is not a major host of brown rot fungi and there have been no reports of brown rot fungi affecting strawberries in Korea. This information supports a likelihood estimate for importation of ‘very low’.
Likelihood of distributionThe likelihood that Monilinia fructigena and Monilia polystroma assessed here would be similar for Monilinia fructigena for apples (Biosecurity Australia 2010a) and table grapes (Biosecurity Australia 2011a) from China and table grapes (Biosecurity Australia 2011b) from Korea, that is: High. Overall likelihood of entryThe overall likelihood of entry is determined by combining the likelihood of importation with the likelihood of distribution using the matrix of rules shown in Table 2.2. The likelihood that Monilinia fructigena and Monilia polystroma will enter Australia as a result of trade in strawberry fruit from Korea and be distributed in a viable state to a susceptible host is: Very low. 4.4.2Likelihood of establishment and spreadAs indicated, the likelihood of establishment and of spread for brown rot is being based on the assessment for apples from China (Biosecurity Australia 2010a), which was adopted for table grapes from China (Biosecurity Australia 2011a), Korea (Biosecurity Australia 2011b) and Japan (Department of Agriculture 2014). The ratings from the previous assessment are: Likelihood of establishment High Likelihood of spread High
4.4.3Overall likelihood of entry, establishment and spreadThe overall likelihood of entry, establishment and spread is determined by combining the likelihoods of entry, of establishment and of spread using the matrix of rules shown in Table 2.2. The overall likelihood that Monilinia fructigena and Monilia polystroma will enter Australia as a result of trade in strawberry fruit from Korea, be distributed in a viable state to a susceptible host, establish in Australia and subsequently spread within Australia is: Very low. 4.4.4ConsequencesThe potential consequences of the establishment of Monilinia fructigena in Australia has been estimated previously for apples from China (Biosecurity Australia 2010a). Monilinia fructigena and Monilia polystroma are considered to have a similar impact. The overall consequences have been estimated to be: Moderate. 4.4.5Unrestricted risk estimateUnrestricted risk is the result of combining the likelihoods of entry, establishment and spread with the outcome of overall consequences. Likelihoods and consequences are combined using the risk estimation matrix shown in Table 2.5.
As indicated, the unrestricted risk estimate for Monilinia fructigena and Monilia polystroma has been assessed as ‘very low’, which achieves the ALOP for Australia. Therefore, no specific risk management measures are required for Monilinia fructigena and Monilia polystroma. Assessments for quarantine pests for which the likelihood and consequence ratings have been determined in a previous assessment4.5Spotted wing drosophilaDrosophila suzukii (EP)The quarantine risks posed by Drosophila suzukii from all countries and for all commodities, including strawberries, were previously assessed in the final pest risk analysis (PRA) report for D. suzukii (Department of Agriculture 2013). Therefore, there is no need to reassess this pest here. A summary of pest information and a summary of the previous risk assessment for strawberries from the final PRA report for D. suzukii is provided here. Drosophila suzukii is native to temperate parts of Asia (Rota-Stabelli, Blaxter & Anfora 2013) and is widespread in Korea (Asplen et al. 2015; Lee 1964). It was also recently introduced into Europe where its distribution has spread dramatically in recent years (Calabria et al. 2012; Cini, Ioriatti & Anfora 2012), as well as North America (Asplen et al. 2015). Drosophila suzukii preferentially oviposit on ripening fruit but will also oviposit on unripe and overripe fruit (Brewer et al. 2012; CABI 2016; Kanzawa 1939; Lee et al. 2011a). Larval feeding causes collapse of the fruit around the area of oviposition and high attack rates can lead to collapse of the entire fruit (Department of Agriculture 2013). Larvae feeding on very acidic fruit fail to complete development (Kanzawa 1935). In its native and introduced range, D. suzukii has been recorded to cause commercial damage to a range of fruits including cherries, blueberries and red bayberries, apricots, plums, strawberries and various caneberries (Lee et al. 2011a). Monitoring programs in the northwest of the United States show trap catches in strawberry fields are high and strawberries are a preferred host for D. suzukii (OSU 2010a, b; Peerbolt 2010). In the eastern United States, high larval infestations in strawberries in North Carolina have been reported (Burrack 2010). Damage to commercial strawberries has also been recorded in Europe (EPPO 2010), with 60–100 per cent damage in infested areas (Grassi, Giongo & Palmieri 2011; Grassi & Pallaoro 2012; Süss & Costanzi 2010). Early in the season, when D. suzukii populations are lower and insecticide application more frequent, infestation levels range from 2–10 per cent (Grassi, Giongo & Palmieri 2011; Grassi & Pallaoro 2012). The risk scenario of concern for Drosophila suzukii is the presence of the larvae and eggs in strawberries.
4.5.1Overall likelihood of entry, establishment and spreadBased on the final PRA report for D. suzukii (Department of Agriculture 2013), the overall likelihood that D. suzukii will enter Australia as a result of trade in strawberries from Korea, be distributed in a viable state to a susceptible host, establish in Australia and subsequently spread within Australia is: High. 4.5.2ConsequencesBased on the final PRA report for D. suzukii (Department of Agriculture 2013), the potential consequences of the establishment of D. suzukii in Australia are: High. 4.5.3Unrestricted risk estimateBased on the final PRA report for D. suzukii (Department of Agriculture 2013), the unrestricted risk estimate for D. suzukii has been assessed as ‘high’, which does not achieve the ALOP for Australia. Therefore, specific risk management measures are required for this pest. 4.6Pest risk assessment conclusionsKey to Table 4.5 to 4.8(starting next page) Genus species (EP): pests for which policy already exists. The outcomes of previous assessments and/or reassessments in this risk analysis are presented in Table 4.6 to 4.8. Genus species (Acronym for state/territory): state/territory in which regional quarantine pests have been identified
N negligible EL extremely low VL very low L low M moderate H high EES overall likelihood of entry, establishment and spread Assessment of consequences from pest entry, establishment and spread PLH plant life or health OE other aspects of the environment EC eradication, control DT domestic trade IT international trade ENC environmental and non-commercial A G consequence impact scores are detailed in section 2.2.3 A Indiscernible at the local level B Minor significance at the local level C Significant at the local level D Significant at the district level E Significant at the regional level F Significant at the national level G Major significance at the national level URE unrestricted risk estimate. This is expressed on an ascending scale from negligible to extreme. Table 4. Summary of unrestricted risk estimates for quarantine pests associated with strawberries from Korea for which a full pest risk assessment is conducted
Table 4. Summary of unrestricted risk estimates for quarantine pests associated with strawberries from Korea for which the URE outcome is adopted from previous assessments
Table 4. Summary of unrestricted risk estimates for quarantine pests associated with strawberries from Korea for which some of the likelihood ratings and consequence estimates are adopted from previous assessments
Table 4. Summary of unrestricted risk estimates for quarantine pests associated with strawberries from Korea for which the likelihood ratings and consequence estimates have been determined in a previous assessments
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