Cucumber green mottle mosaic virus

CGMMV is a plant virus from the genus Tobamovirus. Tobamoviruses are known for their ability to survive in relatively harsh environments without the presence of host material.

There are at least 5 strains of CGMMV, some of which cause symptoms in cucumbers and some that do not.

Symptoms

CGMMV symptoms vary with the type and cultivar of the host plant, environmental conditions, plant growth state at the time of infection and the strain of the virus. In general, younger plants show more severe symptoms, however some host plants show no symptoms.

Cucumber

• Green mottling on young leaves and fruit surfaces.
• Whole plants may collapse.
• Even when leaves are asymptomatic yield losses can occur.

Rockmelon (cantaloupe, muskmelon)

• Young leaves show mottling and mosaic patterns that often disappear from mature foliage.
• Fruit develop different degrees of malformation, mottling and disruption to surface netting.

Pumpkin, squash and zucchini

• Infected foliage can be asymptomatic or show leaf mottling and mosaic patterns.
• Fruit can have no external symptoms but still be internally discoloured and necrotic.

Watermelon

• Mottling and mosaic patterning of young leaves.
• General bleaching of foliage can occur.
• Leaf symptoms may fade in mature plants, and plants may appear to 'recover'.
• Brown necrotic lesions on stems and peduncles.
• Runners, or even whole plants, may die prematurely.
• Fruit can be misshapen with spongy, rotten flesh that can be yellow or show dirty red discolouration.

Seeds

CGMMV can cause physical changes to seed produced from infected host plants. Infected seeds can have:

• hairs on the surface of the seed coats
• extra layers in melon seed coats

Widespread in Asia, Europe, the Middle East and North America. CGMMV is also present in Nigeria in Western Africa.

The first detection of CGMMV in Australia occurred in the Northern Territory in 2014. Isolated detections of CGMMV have also occurred in Queensland (2015 and 2017) and Western Australia (2016).

In Queensland the disease is confined to a couple of properties and there is a containment strategy in place to prevent disease spread

CGMMV infects commonly grown cucurbit crops and gourds, including:

• cucumber or gherkin (Cucumis sativus)
• pumpkin (Cucurbita maxima or Cucurbita moschata)
• rockmelon, aka cantaloupe or muskmelon (Cucumis melo)
• watermelon (Citrullus lanatus)
• snake gourd (Trichosanthes cucumerina)
• zucchini (Cucurbita pepo)
• bottle gourd (Lagenaria siceraria)
• bitter gourd (Momordica charantia).

Common weeds can also be infected including:

• amaranth (Amaranthus species)
• black nightshade (Solanum nigrum)
• common heliotrope (Heliotropium europaeum)
• fat hen (Chenopodium album)
• pig weed (Portulaca oleracea)
• some wild cucurbit plants, such as pie melon.

Once infected with CGMMV a plant is diseased for life, there is no known cure. CGMMV uses the host plants replicating systems to reproduce itself and spread through all the host plant's tissues (roots, stems, leaves, fruit, pollen and seed). The newly-created virus particles are then transferred either in plant sap or through pollen or seed to new host plants to create the next infection.

CGMMV particles are very robust and can survive for long periods on hard surfaces (e.g. tools, equipment, vehicles), beetle mouthparts and in soil and water.

As well as crop host plants, CGMMV can infect a number of weed host plants, the role of these plants in the viruses life cycle is not well understood.

Seeds are the main means of long-distance movement of CGMMV, with infected seed shown to have moved the disease to countries previously free of the disease.

CGMMV is easily transmitted from plant to plant. Due to the very robust nature of its particles, almost anything that has been touched by an infected plant or its sap can transfer the disease. CGMMV particles can remain infectious for months on hard surfaces and for years in soil.

CGMMV is transmitted by:

• pruning, grafting and harvesting tools
• plants rubbing together, especially in nurseries
• seed
• soil
• water, including flood irrigation in fields and nutrient solutions in hydroponic production
• hands of workers
• vehicles, shoes, clothing.

Sap-sucking insects (e.g. aphids, mites, whiteflies) do not transmit CGMMV.

Honey bees (Apis mellifera) can transmit CGMMV through the transfer of infected pollen. It has not been proven that beehives are a source of CGMMV infection, even though CGMMV can be detected in honey, wax and other materials in the hive.

Inspect crops regularly for plants with poor vigour, stunting or reduced yield. Examine these plants for the presence of viral symptoms such as:

• leaf mottling and blistering
• vein clearing
• yellowing
• leaf deformation.

Fruit may not show symptoms on the outside, or may be spotted, streaked or distorted. Fruit can be discoloured or rotting inside.

Report suspected cucumber green mottle mosaic disease to Biosecurity Queensland immediately on 13 25 23 or contact the Exotic Plant Pest Hotline on 1800 084 881.

There is no cure for CGMMV; once infected plants are infected for life. Therefore the most effective means of control is prevention.

There are simple steps you can take to protect your farm:

• Source seeds from reputable suppliers and request for a written statement stating that the seeds (both cultivars and rootstock) have been tested and found to be free from the virus using the enzyme-linked immunosorbent assay (ELISA) method.
• Purchase healthy seedlings from reputable nurseries grown from ELISA tested seed.
• Keep records of where plants/seeds are sourced from and where they are planted on your property.
• Check new plants on arrival to make sure they are healthy and are pest and disease free.
• Regularly check your farm and report any unusual or unfamiliar symptoms.

Protect your farm from plant pests and diseases:

• Protect your farm from emergency plant pests
• Biosecurity manual for the nursery production industry (PDF, 3.1MB)
• Biosecurity manual for Bundaberg horticultural farms (PDF, 1.3MB)
• Understand good farm biosecurity
• Visit the farm biosecurity website

Biosecurity Queensland recommends that cucurbit growers ensure any seed line they purchase or use has been tested by ELISA using a sample size of 9,400 seeds in accordance with the Australian Government Department of Agriculture, Fisheries and Forestry's Public Quarantine Alert (PQA1025) issued on 21 January 2015.

Producers are encouraged to adopt good on-farm biosecurity practices, including on-farm hygiene, to protect their crops from viruses such as CGMMV.

CGMMV is restricted matter under the Biosecurity Act 2014.

Report suspected CGMMV to Biosecurity Queensland immediately on 13 25 23 or contact the Exotic Plant Pest Hotline on 1800 084 881.

If you think you have found CGMMV, you must take all reasonable and practical steps under your control to minimise any associated risks. This is called a general biosecurity obligation (GBO).

Movement restrictions are in place to protect Queensland from CGMMV.