Review of import conditions for fresh taro corms

The likelihood that the French Polynesian strain of Dasheen mosaic virus will arrive in Australia with the importation of fresh taro corms from any country where this pest is present is: MODERATE.

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  The geographic distribution of plants infected with FP-DsMV within French Polynesia is not known.
  
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  Taro plants infected by FP-DsMV are stunted and have severely distorted leaves (Carmichael et al. 2008). Leaves probably also develop mosaic and feathering patterns. The leaves of some infected plants are reduced to strap-like structures without leaf blades (Carmichael et al. 2008).
  
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  It is reported that plants infected with FP-DsMV often do not to recover (Carmichael et al. 2008). However, a few plants may recover and appear healthy.
  
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  It may be difficult to visually identify all plants infected with FP-DsMV. Plants infected with typical-DsMV strains may produce asymptomatic leaves (Nelson 2008) and symptoms may occur intermittently and vary seasonally (Hu et al. 1995).
  
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  It is not known if plants infected with FP-DsMV produce corms.
  
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  The virus is present in the corms of plants infected with other DsMV strains (Zettler and Hartman 1987; Hu et al. 1995; Nelson 2008). Hence, if corms are produced, it is likely FP-DsMV will be present in corms.
  
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  FP-DsMV is probably transmitted by aphids. Plants may be infected by aphids after they have produced corms, and the virus may subsequently spread to the corms.
  
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  The condition of corms that are produced from infected plants has not been reported. Infected plants may not produce commercially acceptable corms.
  
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  It is possible that if infected corms are harvested, some may be indistinguishable from uninfected corms, so corms carrying the virus could escape detection and be exported to Australia.
  

The likelihood that the French Polynesian strain of Dasheen mosaic virus will be distributed in 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, is: HIGH.

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  Imported corms are intended for human consumption. Corms will be distributed to many localities by wholesale and retail trade and by individual consumers. Some corms will be distributed to areas where taro or other aroid species grow.
  
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  If infected corms are imported, they are very likely to be distributed.
  
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  Consumers could discard small amounts of corm waste in urban, rural and natural localities. Small amounts of corm waste could be discarded in domestic compost.
  
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  Discarded corm waste of infected small corm taro may sprout and develop into infected plants.
  
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  Some infected corms of small corm taro may be planted for domestic cultivation instead of being consumed and develop into infected plants.
  

The likelihood that the French Polynesian strain of Dasheen mosaic virus 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, is: MODERATE.

The likelihood that the French Polynesian strain of Dasheen mosaic virus 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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  If a volunteer taro plant grows from a corm carrying FP-DsMV, the plant is likely to be infected with the virus.
  
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  Small corm taro will sprout readily from lateral buds in the corm, and so may be propagated easily (Onewueme 1999). Large corm taro is more difficult to propagate. New plants are likely to be infected with the virus.
  
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  Colocasia esculenta is considered to be native in the Northern Territory, and naturalised in Western Australia, Queensland, New South Wales, and on Christmas Island, Norfolk Island and Lord Howe Island (CHAH 2009).
  
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  Colocasia esculenta was included in a list of the 200 most invasive plants in SE Queensland by Batianoff and Butler (2002). Hicks and Nguyen (2004) cautioned about disposal of waste corms of small corm taro, noting that the plants have the potential to become an invasive weed species.
  
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  DsMV is established where plants are grown from corms, cuttings or bulbs, and may be spread on contaminated pruning tools (Nelson 2008; Zettler and Hartman 1987).
  

The likelihood that the French Polynesian strain of Dasheen mosaic virus 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: HIGH.

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  The aphids Myzus persicae, Aphis craccivora and Aphis gossypii are vectors of typical-DsMV strains and are present in Australia (CABI 2007). FP-DsMV is probably transmitted by these same aphid species.
  
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  FP-DsMV may spread if a vector aphid feeds on an infected volunteer plant and then feeds on healthy taro plants.
  
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  The leaves of plants infected with FP-DsMV are severely distorted and stunted (Carmichael et al. 2008), so infection of a commercial crop is likely to be detected.
  
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  Infected plants in a domestic garden may not be detected.
  
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  Infection of wild taro is likely to go undetected.
  
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  Infection of ornamental aroids by other DsMV strains can be controlled by quarantine and integrated pest management, but it may not be economically feasible to implement such measures for taro production (Zettler and Hartman 1987; Jackson et al. 2001; Carmichael et al. 2008).
  
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  Other DsMV strains can spread rapidly, with more than 50 percent of virus-free plants in trials being infected in 3–10 months (Jackson et al. 2001).
  
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  Very high incidences of other DsMV strains have been reported in Colocasia spp. and in many countries (Zettler and Hartman 1987).
  
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  FP-DsMV may spread to the same extent as other strains of DsMV, and it may be difficult to control.
  
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  FP-DsMV may spread to naturalised and native populations of taro.
  

The likelihood that the French Polynesian strain of Dasheen mosaic virus 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 a susceptible host, establish and spread within Australia, is: LOW.

Assessment of the potential consequences (direct and indirect) of the French Polynesian strain of Dasheen mosaic virus is: LOW.