Posted 6:59 PM by Luigi
Biotechnology fights kava disease

By Richard Davis, SPC Virologist, in Pacific Islands Business.

Kava dieback disease is the single greatest threat to kava growers in the Pacific. This devastating disease, which can destroy entire plantings, was first discovered on the Suva Peninsula in the 1930s. In Fiji today, estimated crop losses average around 40%. Regional research scientists working with biotechnology tools have uncovered the secrets of this disease which causes kava plants to “melt down” and die from a rapidly spreading black rot of stems.
Checking...Nemani Tunidau and Apimeleki Motu examine an experimental kava plant.

For over 50 years kava dieback disease remained a deep mystery for scientists working in the Pacific. Many fungi, bacteria and nematodes (tiny worms in the soil) were investigated as possible culprits. But one by one each was found not to be the cause of the problem.

A major breakthrough was discovering that the kava dieback disease was caused by a virus called cucumber mosaic virus (or CMV for short). This was discovered in the course of Australian funded research in Tonga from 1987 to 1994 which also involved Fiji, Vanuatu and Samoa. Researchers found the virus in kava plants in all four countries. They then artificially infected healthy plants to prove that CMV was causing the dieback.

The discovery that this virus was the cause of kava dieback, as well as being unexpected, was frustrating because virus diseases are hard to control. There is no simple cure, like a chemical spray, for viruses.

Growers over the years have adopted a combination of management practices to deal with virus infections in their crops. CMV is especially difficult to control because it is so widespread, attacking over 1200 plant species. The virus is readily moved around in stem cuttings of kava, and easily spread by aphids.

Growers were advised to remove all diseased plants by digging them out and burning them as soon as spotted. However, kava growers did not like to kill off their own plants. Individual plants are worth a lot of money. Also, farmers knew that following dieback some re-growth normally appears.

New look at the problem

Not much happened after this initial work and farmers continued to struggle with kava dieback. But in early 2002, with new techniques now available to researchers, the Secretariat of the Pacific Community (SPC) allocated funds under the European Union Plant Protection Project to once again look at kava dieback. The researchers were now able to use cutting edge tools of biotechnology to spot the presence of the virus, essentially the same DNA detection methods used in forensic police work.

A small team was quickly put together, comprising researchers from the old campaign and new ones from the Fiji and Tonga agricultural ministries. The task of this team was to learn enough about the virus to be able to recommend a disease management package that would be acceptable to growers, to road test the package and then introduce the techniques to growers.

Central to this second assault on kava dieback was the establishment of new laboratories equipped with virus testing biotechnology. SPC helped furnish two labs at Koronivia Research Station and at the University of the South Pacific's Institute of Applied Science in Fiji.

Breakthrough

The central mystery was: why has kava continued to survive in the face of CMV over so many years? With the aid of the new technology, the researchers discovered the likely answer. They found how the kava plant defends itself against the virus. Firstly, infected kava plants do not allow the virus to move around easily within them and, secondly, most new growths are free of the virus, a very unusual thing in the world of plant viruses.

This breakthrough suggested that removing diseased stems as soon as they appear could offer effective control of the disease. By harnessing the natural ability of kava to fight off the virus and combining this with other management techniques, it is hoped the disease can now be conquered.

Best practice management

To keep disease levels low in the field, growers must plant kava in amongst other plants that do not play host to CMV (intercropping). Small isolated plantings are best, using disease-free stock planted under shade trees that are non-host to the virus, in good kava soil so that the plants will be strong and better able to resist the virus. This package of best practices is now on trial in Fiji and Tonga.

Disease-free planting material is a key part of the control strategy. Here again, biotechnology offers hope. Researchers at SPC's Regional Germplasm Centre have recently developed tissue culture techniques for kava. This will allow rapid multiplication of healthy kava plants for distribution to growers.

The future looks bright for kava production in the Pacific.