TR4 response….. protecting bananas

Last month marked two years since Panama Tropical Race 4 (TR4) was first detected in Queensland’s Far North, on a farm in the Tully Valley. As the anniversary neared, leading banana researchers from across Australia met to discuss the latest applied research and breakthrough technology that continues to focus on the short- to long-term management of the disease. 

Tony Pattison and Tegan Kukulies report.

Since its initial detection in North Queensland, Panama TR4 has brought many challenges to banana growing, production and the industry at large.

In the two years since detection, banana growers have become much more aware of the disease, and most have implemented effective on-farm biosecurity. Practical banana research is heading toward reducing the impacts of the disease.

There is a long history of research on Panama disease throughout Australia. The use of applied research and cutting-edge technology by banana researchers from the Department of Agriculture and Fisheries (DAF) (agri-science and biosecurity), University of Queensland, James Cook University, Northern Territory Department of Primary Industries and Resources, New South Wales Department of Primary Industries and the University of New England was discussed at a recent workshop in Brisbane.

The latest research and development aimed to improve growers’ confidence in disease containment, reduce disease spread and provide farm management options if the disease became widespread.

One of the first questions North Queensland banana growers asked when TR4 became a reality was, “How do I protect my property?”

Implementing effective on-farm biosecurity is paramount. New management strategies are being developed using revolutionary studies on the genetics of the Fusarium fungus, the cause of Panama disease.

Containing the disease on the single, infected property has also been a priority, and improving our knowledge of containment by establishing the most effective destruction of infected plants continues to be a primary goal.

However, in the event that Panama disease did spread, options for managing the disease and its impacts on the banana industry need to be developed. The creation of banana plants with better resistance is underway, by manipulating the tissue culture process.

When Australia’s leading scientists researching aspects of Panama disease met in Brisbane in February, they discussed a range of exciting research; what is new, in progress and on the horizon. Here, we take a snapshot of their innovative work.

What’s new?

Extensive research into the use of disinfectants has shown the quaternary ammonium (QA) group of chemicals to be very effective.

The initial disinfectant testing, which was conducted using Panama disease Race 1, is now being tested using Panama TR4 in the Northern Territory (NT). Testing so far shows that products — for example,  products containing 120g/L didecyl dimethyl ammonium chloride (QA) made up at 1% — are also effective on Panama TR4.

Further testing is also showing that detergents (such as Farmcleanse) can actually de-activate disinfectant products, if mixed directly. Therefore, growers should ensure they have thoroughly washed off detergents, before applying disinfectant products.

Dip and compare colour test strips have also shown promise, with testing currently being finalised. Also in this space, there is good news for growers that have a shuttle or spray tank and don’t regularly make up QA disinfectant solutions. Using the test strips as indicators, disinfectant solutions (1% QA products), which have been left in a sealed container exposed to the elements of the weather (full sunlight), have remained at a 1% solution for 12 weeks. Initial testing is also showing that these disinfectants are no more corrosive to a range of metals than water. Together, the use of colour test strips and metal corrosion tests are helping banana growers make sure chemicals are being used effectively.

Current destruction protocols of infected plants involve bagging the plants, gouging growing points and applying high rates of urea to infected plant material, as well as the soil immediately surrounding it. Results from a novel lab bioassay and a field trial in New South Wales (NSW) (using Subtropical Race 4) demonstrated that this was an effective method to quickly kill the Fusarium fungus.

Surveys of weed and groundcover species from Panama Race 1 sites in North Queensland and Subtropical Race 4 sites in NSW, identified that some weed species are alternative hosts to Panama disease. A pot trial with 18 common weed and groundcover species revealed that under controlled conditions, Fusarium could be recovered from all 18 species. Where and how the Fusarium is surviving on the weeds needs to be clarified and how this translates to the field.

What is in progress?

There are some exciting advancements in understanding the Fusarium genetics. Genetics is another language to most of us but, in a nutshell, there are many different Fusarium species, each with their own individual ‘barcode’. Researchers are analysing the differences in these ‘barcodes’ to better understand their relationships with each other, and which segments may be responsible for causing Panama disease.

Under strict quarantine conditions scientists have also manipulated the Fusarium fungus to ‘glow’ in order to better understand where and how the fungus moves through banana plants. This research is important to help understand how the fungus moves through the banana plants, to cause disease symptoms which lead to plant death.

The first trial looking at the effect of nutrients on Panama Subtropical Race 4 development has commenced. Using a controlled aeroponic system (soilless), disease development is going to be monitored following different application rates of boron. Other nutrients will be evaluated following learnings from this initial trial. In addition to this, an extensive soil type survey is being conducted on North Queensland banana properties’ characterising differences in soil characteristics, and understanding how these differences attribute to suppression of Panama disease.

Scientists are continuing to apply mutagenesis techniques to tissue culture banana plantlets in an attempt to develop a commercially viable banana cultivar with improved tolerance to Panama TR4.   In a multi-pronged approach, firstly mutagenesis has been applied to GCTVC 119 in an attempt to improve tolerance to the disease and also Gold Finger in an attempt to improve agronomic and eating quality. The first plants produced from this approach are expected to be planted in the NT soon.

What is on the horizon?

Genome sequencing and soil community profiling are just two of the methods that will be applied to help understand the role soil biology may play in suppressing Panama disease. An array of methods will be used to monitor the soil biology following varying practice changes, such as the use of different cover crops. Different cover crop options are currently being evaluated in a pot trial and this will help determine which species will be used in a cover crop field trial in the NT.

Clean planting material is a key priority for minimising the risk of spreading TR4. Negotiations are nearing completion to develop a Quality Banana Approved Nursery (QBAN) Scheme ‘replacement’, which is anticipated to be merged under the Nursery Industry Accreditation Scheme Australia biosecurity system, which will be ultimately certified by the Australian Banana Grower’s Council. This improved system will give growers renewed assurance that tissue culture producers, that are certified under the new system, continue to supply clean disease-free planting material.

The hard copy of the On-farm Biosecurity BMP, developed as a ‘sister’ program to the industry’s well adopted Banana BMP Environmental Guideline, is nearing completion. The resource aims to set industry guidelines for on-farm biosecurity practices through the use of a self-assessment checklist, similar to that of the BMP Environmental Guidelines.

These projects have been funded by Horticulture Innovation Australia Limited using the research and development banana levy with co-investment from the Queensland Department of Agriculture and Fisheries and funds from the Australian Government.