New banana cultivars will help in Panama TR4 fight

So said Professor Randy Ploetz at the Australian Banana Congress 2017 in Sydney last month, prior to the detection of another suspected outbreak of Panama Tropical Race 4 (TR4) disease on a Tully property in July.

There are few people more qualified to speak about TR4, with Professor Ploetz discovering the disease in Taiwan in 1989.

In giving an update on international research on the disease's management, he said there were some realities Australian growers would need to come to terms with.

"Whenever anyone considers managing this, you need to consider economic management," Professor Ploetz said.  

"Can you continue growing bananas the way you were?"

Professor Ploetz listed off several of the management techniques tried for TR4 such as fumigants, flooding and suppressive soils but said each was limited in its own way.

He had particular question-marks over biological controls.

"The ones that have done field studies show, clearly, that you don't get sustainable management. It's in two or three years later you get tremendous disease," he said.

"Bio-control unfortunately does not work for this crop.

"To me, history has shown clearly that the only sustainable way to manage this problem is with resistant cultivars.

"It's going to be really difficult to come up with a Cavendish-like cultivar through conventional measures that would resist this disease and would have all the other characteristics you would want in a Cavendish cultivar.

"Consider all options before you say, no, I can't manage this disease."

He spoke of somaclones, plants produced through micropropagation that are genetically identical to the original plant, but said they generally have longer production cycles and lower yields, plus some have a problem with splayed fingers.

Front row observer

Professor Ploezt has watched the disturbing development and spread of banana diseases throughout the globe in the past 30 years.

He said the original strain of Panama disease (race one) virtually wiped out the most prolific banana variety, Gros Michel, until the Cavendish was widely adopted due to its resistance to the strain.

"More recently, and more scary to me, is the popping up of TR4 around the world," Professor Ploetz said.

"This problem is really serious. So the fact that you are taking it really serious here in northern Queensland and you've come to grips with it in the Northern Territory, is good because this is probably the most serious disease for bananas.

"I work on a lot of different diseases in bananas but this one is really pernicious."

One of the aspects to TR4 which is difficult for many to come to grips with is its longevity in a paddock.

TR4 can remain within a block for a decade or more.

"Once you have a field infested with this pathogen, whether it's race one or TR4, it's in that field for a very long time," Professor Ploetz said.

"I can't overstate the importance of that. Once you've got an infested field, you can't go back to that field with that same cultivar and expect to produce that cultivar. It's just impossible."

He said he thought one of the main reasons the pathogen stays on for so long is that certain weeds can act as hosts, thus he encouraged those undertaking research into TR4 weed hosts.

"It's a no-brainer that if you establish new plantings in an area and you've got this disease, you do not want to use traditional suckers so tissue culture plantlets are free of this pathogen," he said.

Practice changes

While he said some researchers have spoken and written on the effectiveness of healthy, clean soil acting as a suppressor to TR4, he said it was the weeds that helped the pathogen to linger, and said tissue culture plantlets were the way to go for new plantations.

Banana growers may need to re-consider how they irrigate as well, with the pathogen easily held in surface water sources.

The disease was rapidly spread in China by pumping from infected water sources, essentially inoculating entire plantations.

"If you have the potential to use bore hole water when you irrigate, I highly recommend that," he said.

"If it gets into the Tully River, using that water is going to be hazardous."

When it comes to biosecurity, Professor Ploetze said growers should seek out the best sanitary products available to wash down machinery, tools and to use in footbaths.

He said footbath solutions are very effective provided no organic material or large amounts of soil sit within them.

Where is it now?

The question for many in north Queensland currently is: How widely spread is TR4?

"We really don't know," Professor Ploetz said.

"Certainly on that first property that was quarantined and eliminated, it was widespread in it, but how widespread outside that plantation, might it be?"

One of the problems with discovering TR4 is that it requires detecting symptomatic plants and by the time they're found, the disease is probably wider spread already.

"We haven't developed a technique to efficiently and effectively detect the pathogen in non-symptomatic situations," he said.

But north Queensland growers received a pat on the back for their vigilance so far.

"The good thing there is people are on red alert. They are aware of how difficult this problem is to manage and they are aware that you're not going to come on my plantation unless you have clean boots, and that we are going to hose you down, and so forth," he said.

He encouraged Biosecurity Queensland to keep up its visual inspections of banana plantations, and also floated the idea of using aerial examination to assist.

American avocado growers currently utilise technology which can detect laurel wilt in orchards through special cameras and algorithms.

Professor Ploetz said it would not be unreasonable to suggest similar developments could be created to help identify TR4.

"We're able now to, with specific spectre of visible and non-visible light, significantly distinguish the plants that are affected early on by this disease (laurel wilt) from other situations," he said.

Australian Banana Growers’ Council R&D manager, Dr Rosie Godwin, spent a week in June with Professor Ploetz and French banana researcher, Dr Frédéric Bakry, travelling north Queensland banana production areas, meeting local scientists and giving the visiting researchers an insight into Australian banana production and biosecurity practices.

“The banana industry is fortunate to have significant investment in fundamental and applied research projects which are targeted at finding solutions to the many pest and disease threats the industry faces,” Dr Godwin said.