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Cucumber green mottle mosaic virus in Queensland, Australia

A ProMED-mail post <http://www.promedmail.org>
ProMED-mail is a program of the International Society for Infectious Diseases <http://www.isid.org>

Date: Thu 4 May 2017

Source: Australian Broadcasting Corporation (ABC) [edited] <http://www.abc.net.au/news/2017-05-04/cucumber-green-mottle-mosaic-virus-imported-seed-biosecurity-qld/8494354>

Biosecurity authorities are trying to figure out how [cucumber green mottle mosaic virus (CGMMV)] disease broke out in Queensland. CGMMV has recently been discovered on 5 local properties, owned by two growers.

Biosecurity Queensland's Mike Ashton said there was a possibility the virus was brought [in] by imported seeds, considering the businesses operate independently and do not share personnel and equipment."We're doing tracing investigations to identify the source."

Farmers are angry [and] blame biosecurity authorities. "We've lost confidence in the biosecurity system," [a farmer] said. "It's simply not working." The Federal Agriculture Department introduced mandatory imported seed testing to combat CGMMV in 2014. Outbreaks of CGMMV, tomato potato psyllid [and] chestnut blight are among those [currently] having an impact on Australia's horticulture.

[Byline: Jonathan Hair]

Communicated by: ProMED-mail <promed@promedmail.org>

[_Cucumber green mottle mosaic virus_ (CGMMV; genus _Tobamovirus_) is a major pathogen of cucurbit crops with reported yield losses of around 15 per cent. The virus has a narrow host range. Many strains, including the type strain occurring in Europe, are limited to Cucurbitaceae, but some isolates have been reported which can also affect a number of species in other families, including Amaranthaceae and Solanaceae. Symptoms vary in different host species and may be masked in field crops. They may include severe leaf mosaic, deformation of vines and internal fruit symptoms such as discolouration and rotting of flesh.

CGMMV is both seed and pollen transmitted. It is extremely stable and can also be spread by mechanical means (human activities, insect damage, plant-to-plant contact), with contaminated agricultural tools, infected plant material, contaminated soil and in water. Spread by specific insect vectors appears doubtful. Disease management may include removal of virus reservoirs, phytosanitary practices and use of certified clean seed or other planting material. Transgenic rootstock lines of some cucurbit crops (such as watermelon) with resistance to CGMMV have been or are being developed.

In Australia, CGMMV has been detected in Northern Territory, Western Australia and Queensland in cucurbit crops (including watermelon, pumpkin), cucurbit seedlings (for example, cucumber) and a number of weed hosts (see previous ProMED-mail posts listed below). Initially, it was suggested that the virus may have entered the country with infected watermelon seed from overseas. However, its presence in multiple hosts could suggest that the virus may have been present in the country before its 1st official confirmation (ProMED-mail post http://promedmail.org/post/20141009.2844854). Wild cucurbits, which are common in central Australia, may have provided a virus reservoir.

Alternatively, different strains may be present in crops and weeds, in which case the strain(s) affecting the crops may have been introduced on seeds. To clarify these questions, strains from the different hosts need to be characterised. Regardless of the original virus source, evidence suggests that local spread occurs (see ProMED-mail post http://promedmail.org/post/20160123.3958997).

The argument for a seed introduction stated for the case above is very plausible. In the light of this as well as past outbreaks having been linked to imported seeds, the farmers are well justified to question the Australian seed certification process and the wider national biosecurity system.

Maps

Australia (with states):

<http://ontheworldmap.com/australia/large-detailed-topographical-map-of-australia.jpg>

Queensland:

<http://www.sydney-australia.biz/maps/queensland/graphics/queensland-maps-australia.png>

Pictures

CGMMV affected cucurbit fruits:

<http://www.english.vkm.no/eway/imgstore/6efd6060bc.jpg> (cucumber), <https://www.agric.wa.gov.au/sites/gateway/files/cucumber%20green%20mottle%20mosaic%20virus1.jpg>

(watermelon) and

<http://www.abc.net.au/news/image/5751900-3x2-340x227.jpg>

(watermelon)

CGMMV symptoms on cucurbit leaves and vines: