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Cucumber green mottle mosaic, unspecified hosts in the Northern Territory of 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 14 Jan 2016

Source: Australian Broadcasting Corporation (ABC) Rural [edited] <http://www.abc.net.au/news/2016-01-13/plant-virus-cgmmv-outbreak-on-nt-government-farm/7086224>

Devastating plant virus on government research farm

A plant virus which wiped out a large part of the Northern Territory's watermelon industry has been discovered at a government facility near Darwin. The Northern Territory Government has confirmed that _Cucumber green mottle mosaic virus_ (CGMMV) has been detected at 2 separate areas of its Berrimah Research Farm. CGMMV was 1st detected in the Northern Territory back in 2014 [see ProMED-mail post http://promedmail.org/post/20141009.2844854].

Ian Curnow, Department of Primary Industry, said the sites had been placed under quarantine. "Berrimah Farm will adopt the same controls as industry to minimise the risk of transferring CGMMV." [He said] that there was "no risk" of the virus spreading to nearby properties [see comment below].

He said the outbreak would not affect the arrangements to lift quarantine restrictions on NT growers in February [2016]. "There will be no interstate trade restrictions on produce."

He said the outbreak had been found before Christmas during routine testing, but due to testing facilities being closed over the holidays, the results were only confirmed last week. "As soon as we had a suspicion of CGMMV we immediately implemented full quarantine restrictions and destroyed all affected plant material by spraying," he said.

An independent investigator would be appointed to examine the Department's biosecurity policies and procedures. "Any recommendations will be shared with industry stakeholders. We know that the seedlings grown on this site tested negative for CGMMV in October last year [2015], which means we can narrow the focus of the investigation."

[byline: Peta Doherty]

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, in water and contaminated soil. 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 2 cucurbit crops, watermelon and pumpkin, as well as a number of weed hosts in the NT (ProMED-mail posts http://promedmail.org/post/20141009.2844854,

http://promedmail.org/post/20141027.2904033 & http://promedmail.org/post/20150226.3195501). Initially, it was suggested that the virus may have entered the country with infected watermelon seed from overseas. However, its presence in these multiple hosts would now suggest that the virus may have been present in the country before its 1st official confirmation, perhaps on wild cucurbits, which are common in central Australia and may have provided a virus reservoir. Alternatively, different strains may be present in the crops and the 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. In the NT, CGMMV has been officially declared as no longer being eradicable.

In the report above, the sudden appearance of the virus on previously virus free (cucurbit?) seedlings at multiple sites within the farm would suggest that local spread does occur, and therefore the claim that there is "no risk" of the virus spreading to nearby properties cannot be justified. Considering the virus can be spread by windborne pollen and that reservoir hosts are widespread, such a statement, as well as the decision to lift all quarantine restrictions on cucurbit crops, appears incomprehensible.

Maps

Australia (with states):

<http://www.webookaustralia.com/images/australiamap.jpg>

Northern Territory:

<http://www.ozhorizons.com.au/maps/northern_territory_map.php>

Pictures

CGMMV symptoms on cucurbit leaves and vines:

<http://phamnhatlinh.files.wordpress.com/2012/05/greenmosaic.jpg>,

<http://www.nt.gov.au/d/cgmmv/Content/Image/gallery/CGMMV%20watermelon%20leaf%20mottling%20Credit%20HM%20Clause%20Inc.jpg>

and

<http://docsdrive.com/images/academicjournals/ijv/2011/fig2-2k11-1-12.jpg>

(also on _Chenopodium_ indicator)