Improved management options for cucumber green mottle mosaic virus (VG15013)

What was it all about?

This project, which ran from 2016 to 2019, investigated how the cucumber green mottle mosaic virus (CGMMV) is spread in cucurbit production as well as alternative hosts for the virus and farm biosecurity protections that growers can implement. CGMMV was first detected in the Northern Territory in September 2014 and the key research areas of this project were to:

• Determine the importance of weeds, non-host plants and honey bees in spreading CGMMV
• Examine the potential for in-field diagnostics to assist rapid detection of the virus on-farm
• Develop extension materials to assist growers with management options, including on-farm biosecurity protocols.

Key findings included…

CGMMV alternative hosts and non-hosts

Six crops were found to be non-hosts of the virus, providing potential alternative cropping options for growers: sweet corn, snake bean, capsicum, okra, sorghum and peanut.

Weed species common in these production areas were surveyed and then tested for the ability to host the virus. The following species were found to carry the virus:  wild melon, wild luffa, amaranth, pigweed, black nightshade, fat hen, wild gooseberry and sabi grass. Further work is needed to find out if these weeds spread the virus to crops.

Understanding CGMMV spread in contaminated soil

Previous work in the NT showed that the virus could remain viable for 12 months without host plants, but in this project the researchers found shorter periods for infection.  Seedlings transplanted into potting mix contaminated with CGMMV resulted in 11/100 plants becoming infected. When seeds were directly sown into the potting mix with CGMMV sap, it was found that CGMMV only remained infectious in soil up to 36 weeks. Damaged root systems seem to allow the virus to infect plants.

Improving CGMMV diagnostics for plant and seed

The team improved a field immunostrip test to effectively detect CGMMV, but other viruses can confuse the test. Laboratory testing is still required to be certain of infection.

Determine the importance of weeds, non-host plants and honeybees in disease spread

A variety of bee products were sampled and viable CGMMV was found in adult bees, pollen and honey. When specific hives were sampled repeatedly over time, only the honey remained infected with CGMMV.

The research team held grower meetings in affected areas, and developed grower resources in several languages.

Grower recommendations

• Plant only clean seed that has been tested at 9,400 seed numbers per batch
  
  
• Avoid sharing seed and if you do, make sure it has been tested
  
  
• Do not save seed from any plant or crop suspected of being infected with CGMMV
  
  
• Adopt and maintain on-farm biosecurity procedures, including ‘Come clean, go clean’ routines and disinfection of tools, equipment, machinery and footwear, particularly when moving from an area infected with CGMMV
  
  
• Plant crops in clean soil and grow non-hosts plants in infested CGMMV soils to reduce the virus load in the ground
  
  
• Early detection is key to minimize the spread of disease and economic impact. Learn to recognize CGMMV symptoms early and avoid disturbing the area once infection has been identified. Isolate any symptomatic plants with a buffer zone
  
  
• Find out where any beehives that come onto your property have come from, to prevent infection from honeybees
  
  
• Use the redeveloped field immunostrip available from Agdia but also send samples into your state diagnostic laboratories for confirmatory testing
  
  
• Seed testing of Asian cucurbits is reliable for subsamples up to 500 seeds for most species except cucumerina where the sample size should not exceed 250 seeds.

ACT NOW

• Watch a short video on the virus and how growers in the NT implement on-farm biosecurity to protect themselves.
  
  
• Download the fact sheets on:
  • CGMMV in Australia
  • Symptoms of the disease and how growers can identify it
  • Non-hosts of the virus
  • Weed hosts of the virus.
    
    
• Download a farm biosecurity plan template for CGMMV and NT Cucurbit farms to work out how to protect your enterprise from the virus
  • This template is also available in Vietnamese and Khmer
    
    
• Read a fact sheet for beekeepers to find out about management practices to minimise CGMMV in honey bee hives.
  
  
• Contact NT Farmers to get help completing a CGMMV farm biosecurity plan, on 08 8983 3233 or idm@ntfarmers.org.au.