AU: Leading the way in Australian banana research

Australia has some of the world leading researchers when it comes to banana diseases. Studies are currently underway at both a basic level, and at an applied level, and recently the mix of the two have helped make important breakthroughs in the industry. 

At the Australian Banana Industry Congress in Sydney, six researchers were given three minutes each to give an update on their research at a presentation called Science Speed Talks.

Fusarium is more commonly known as Panama disease, and has been found throughout the world, including an isolated discovery in Tully in North Queensland in 2015. The banana infecting strains of Fusarium fungus are known as Fusarium oxysporum cubense (FOC). 

Liz Czislowski is in the final year of her PHD at the University of Queensland, and her research is targeted at what sets race 4, from races 1 and 2 at a genetic level. It is known that races 1 and two are present in Lady Finger, but not Cavendish, but TR4 affects both cultivars.

"To answer this question, I got together isolates that represented this variability in pathogenicity and I wanted to capture all the genetic information for these isolates," Ms Czislowski said. "To do this I extracted DNA from these islets and I set them through a process called whole genome sequencing. Once I sequenced them, I generated datasets for each of the isolates. I was able to search these datasets for a group of pathogenicity genes, which we call Secreted in Xylem (SIX) genes." 

Ms Czislowski then began looking for what SIX genes were in FOC and while all copies had them, but race 4 had more. She also found that some SIX genes that were specifically in race 4 but absent in races 1 and 2. 

"So we are now interested in how the pathogen uses these SIX genes during infection," she said. "This research is ultimately about understanding the genetics regulating pathogenitcy in FOC, including TR4. A better understanding of this enemy means we can develop more effective and targeted control strategies."

Sharl Mintoff is senior plant pathologist from the Northern Territory Department of Primary Industries, which is involved in a trial of different varieties. The point of trial is to figure out which variety has highly tolerant or are resist to TR4.

"Among those plants there are 27 different varieties," Mr Mintoff said. "When we screen them we are looking for internal and external symptoms." 

As well as for symptoms assess the plants up until the first ratoon, but Mr Mintoff admits it is a bit difficult as different varieties have different bunch times, so the study is only halfway through. 

"So from the work so far, the Cavendish, the Williams and the DTM25 they generally don't make it to harvest," he said. "You usually get pretty severe internal symptoms. But it is not all doom and gloom, as we have a few varieties that look good so far."

The research is still in mother plant stage, but Mr Mintoff and his team are hoping to create to use the successful variety to develop as an alternative.

Plant pathologist at Queensland Department of Agriculture and Fisheries (QDAF), Noeleen Warman recognises that Fusarium oxysporum cubense, or Panama disease, most destructive diseases that can devastate entire crops resulting in production and economic losses.

She admits there is a lot of research about the initial infecting process from the soil and into the roots, but her studies focus on what happens once the pathogen has gained access and where it moves in the aerial parts of the plant.

"Therefore an understanding of how the pathogen moves above the soil and throughout the plant is essential to ensure the preventative measures are effective," she said. "To answer my questions, my research used an isolate of FOC TR4 along with a green florescent protein, to visualise how the pathogen moves within the plant."

Under strict glasshouse conditions, using both susceptible Lady Finger and Cavendish cultivars, the whole plants were examined microscopically.

"The results were interesting to say the least," Ms Warman said. "FOC was visible in the pseudo-stem of the plant, prior to external symptoms being developed. Furthermore, once the infected leaf-sheath begins to die, the pathogen moves from the inside of the leaf-sheath to the surface. Once on the surface, the pathogen produces masses of spores, making decaying leaves a major source of inoculum."

She admits these observations raise additional questions about the potential spread, via insects, animals or even human contacts. Another issue she raised was does de-leafing return inoculum to the soil, even if plants are not showing any symptoms.

Jenny Cobon from QDAF has focused her research on root health and nematodes. She says they roots absorb nutrients and water for growth, so they can produce a crop, but they are also the prime target for a number of plant parasitic nematodes.

There are many plant parasitic nematodes that can cause damage to crops. It is still not known what the extent of the damage is or how to manage them. Ms Cobon says the burrowing nematode is the most severe nematode pest, and where most of the research has been based.

"Crop monitoring has resulted in knowing the extent nematode damage and saw a reduction in nematocide use," she said. "But crop monitoring may now need to be updated, to account for the damage the other nematodes can do."

Very few chemicals are available to banana growers, but Ms Cobon recommends rotation in fields for new plantations. But due to host specificity she says it is important to correctly identify all the nematodes in the soil, as different rotations may be required to supress different nematodes.

"Different crop rotations will be needed to supress lesion nematodes in New South Wales, compared with rotations to supress burrowing nematodes in North Queensland," Ms Cobon said.

She says clean planting material is the best way to plant a new field, and tissue culture plantlets are preferred as they are disease free. While improving soil health, can help supress an attack from nematodes.

Ms Cobon believes the next challenge is to build on the knowledge, and learn more about all plant parasitic nematodes, because "no roots mean no fruits".

Donna Chambers has been an entomologist at QDAF, and is based in North Queensland, and recognises controls for thrips have not changed for over 20 years, and still use a handful of chemicals. But she has been researching alternatives, sighting that current chemicals are becoming deregulated and insects are becoming resistant.

Specifically, she is looking whether thrips are attracted to certain colours, in bananas. Lurem T is a commercial lure is a general thrips attractant developed from post plant compounds.

"The first trial compared four colours; green, yellow, blue and white against a clear control," Ms Chambers said. "Five sticky traps of each colour were nailed to the stem, opposite half-filled unbagged. Blue traps attracted twice as many rust thrips as white and four times as many as the other colours. Blue and White sticky traps equally attracted more flower thrips."

The second trial used ten blue sticky traps together with Lurem T lures against ten sticky traps without lures. Lurem T was an attractant to flower thrips, but caught very few rust thrips. Lures attracted two and a half more flower thrips than the other traps. 

She says this pilot testing provides the basis for more extensive trials to investigate colour preference, trap design and lure selection. 

"The use of lures (and colour) may lead to possible control tools that don't rely on chemicals" she concluded.

QDAF's senior horticulturist Trevor Parker has a strong interest in technology, and improving irrigation and pest control. He says a project is investigating if to see satellite imagery can improve productivity and identify stress in banana plantations.

The technology has been used accurately to map crop variability and product yield. Satellite imagery is the measure of solar reflectance and absorption properties of a growing canopy. A mapping tool created from satellite imagery is NDVI.

"NDVI is used to measure the amount and quality of chlorophyll in a growing canopy," he said. "NDVI is used to map the variability of crop health. Low NDVI values correspond with stress and low biomass, whilst high NDVI are areas of high biomass and high crop health." 

He says NDVI is validated by yield, crop health, soil fertility and water stress.

"Results so far have identified that NDVI can accurately identify variability in tree vigour across an individual block and areas of high NDVI are producing a higher yield," Mr Parker said. "Although encouraging, harvesting and de-leafing complicates matters, as some areas showing low NDVI values in fact provided a high yield."

The challenges are being addressed by acquiring multiple images throughout the growing season to allow the full cycle to be mapped. A combination of the images will show areas that have reached full potential and underperformed, and allow for investigations into productivity and maximising yield.