Unrestricted risk estimate

The unrestricted risk for Corallomycetella repens is: NEGLIGIBLE.

Unrestricted risk is the result of combining the probability of entry, establishment and spread with the outcome of overall consequences. Probabilities and consequences are combined using the risk estimation matrix shown in Table 2.5.

The unrestricted risk estimate for root rot of ‘negligible’ achieves Australia’s ALOP. Therefore, specific risk management measures are not required for this pest.

The likelihood that Rosellinia pepo will arrive in Australia with the importation of fresh taro corms from any country where this pathogen is present is: LOW.

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  Taro is only a minor host of Rosellinia pepo (CABI 2011).
  
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  Rosellinia pepo is present on the roots as greyish cobweb-like strands that become black and coalesce into a woolly mass (ten Hoopen and Krauss 2006). Following infection, the roots and stem base are quickly surrounded by this mat of dark hyphae. This hyphal mat produces synnematal conidiophores, which produce large numbers of conidia (CABI 2011). The hyphae are visible to the naked eye on the surface of the roots and corms (CABI 2011) and would be obvious on fresh taro corms at harvest or during pre-export processing. Infected corms are unlikely to reach the export stream.
  
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  Ascomata are only formed at a late stage once the plant tissues have been dead for some time (CABI 2011) and so contaminating ascospores are unlikely to be present on taro corms. The role that ascospores play in disease epidemiology is unclear (Oliveira et al. 2008).
  
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  Rosellinia pepo is a soil-borne pathogen, and importation would be more likely if taro corms were contaminated with soil or other organic matter. Cleaning corms to remove soil and organic matter during commercial harvest and grading operations will reduce the presence of infectious material.
  

The likelihood that Rosellinia pepo will be distributed within Australia in a viable state to a susceptible part of a host, as a result of the processing, sale or disposal of fresh taro corms from any country where this pathogen is present, is: MODERATE.

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  The infected corms are likely to be obvious during inspection and packing for distribution, leading to infected corms being discarded early in the distribution chain.
  

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  Corms will be distributed to many localities by wholesale and retail trade and by individual consumers.
  
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  Mycelia present on the corms would remain infectious if humidity was high during transit.
  
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  Consumers will carry small quantities of taro corms to urban, rural and natural localities. Small amounts of corm waste could be discarded in these localities.
  

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  Small amounts of corm waste could be discarded in domestic compost.
  
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  Mycelial growth and transmission to new hosts could occur where infected corms were discarded in proximity to organic matter and suitable plant hosts.
  
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  Rosellinia pepo is a tropical species, and it is unclear what effect cool conditions during storage and transit of taro corms would have on pathogen viability. Storage of cultures at 5 °C on different substrates proved possible for up to two years (ten Hoopen and Krauss 2006).
  

The likelihood that Rosellinia pepo will enter Australia and be distributed in a viable state to a susceptible host, as a result of trade in fresh taro corms from any country where this pest is present, is: LOW.

The likelihood that Rosellinia pepo will establish within Australia, based on a comparison of factors in the source and destination areas considered pertinent to its survival and reproduction, is: MODERATE.

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  Rosellinia pepo is plurivorous, affecting many woody and sub-woody crops. Hosts, including avocado, banana, breadfruit, coffee, lime, mangosteen and rubber (Oliveira et al. 2008) are present in many parts of Australia.
  
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  Rosellinia pepo can survive on organic matter in the soil (Oliveira et al. 2008).
  
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  Root rot associated with Rosellinia spp. is often associated with high soil humidity, acid soils and a high percentage of organic matter (ten Hoopen and Krauss 2006). Disease is less likely to establish in areas of low rainfall frequency, where little organic matter accumulation occurs and where there is low shade and uneven ground (Oliveira et al. 2008). Only parts of northern Australia are likely to present suitable habitats and conditions for establishment.
  

The likelihood that Rosellinia pepo will spread within Australia, based on a comparison of those factors in the source and destination areas considered pertinent to the expansion of the geographic distribution of the pest, is: MODERATE.

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  Opportunistic soil-borne pathogens such as Rosellinia spp. are difficult to control once they become established (ten Hoopen and Krauss 2006).
  
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  Dissemination is based on contact between infected and healthy roots, or by fungal growth on organic matter in the soil (ten Hoopen and Krauss 2006). Rainwater can carry infected materials and plant debris throughout the soil (Oliveira et al. 2008).
  
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  If the fungus did manage to establish in a suitable habitat, then it would spread into adjacent climatically similar habitat, as it possesses a wide host range.
  
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  Climatic conditions (particularly temperature and humidity) would limit its spread as a pathogen to the northern parts of Australia.
  

The likelihood that Rosellinia pepo will be imported as a result of trade in fresh taro corms from any country where this pathogen is present, be distributed in a viable state to susceptible hosts, establish and spread within Australia, is: LOW.

Assessment of the potential consequences (direct and indirect) of Rosellinia pepo for Australia is: LOW.