By Michael Slexak
A multibillion-dollar banana industry at risk of a deadly disease could be saved by genetic modification that created a line of bananas resistant to Fusarium wilt tropical race 4, also known as Panama disease.
Researchers at Queensland University of Technology genetically modified Cavendish bananas using a gene found in a south-east Asian banana subspecies that naturally displayed resistance.
They created one line of Cavendish bananas that remained completely disease-free over the three-year trial, and three lines that showed very strong resistance.
Tropical race four – which emerged in Taiwan in the 1980s and spread through Indonesia, Malaysia, the Philippines, China and Pakistan – is a soil-borne fungus that can survive for more than four decades in the ground. It can not be controlled with chemical agents.
The trial leader, Prof James Dale, said the results were a major step
towards protecting the US$12bn (A$17bn) Cavendish global export
“TR4 can remain in the soil for more than 40 years and there is no effective chemical control for it,” Dale said. “It is a huge problem.
“It has devastated Cavendish plantations in many parts of the world and it is spreading rapidly across Asia. It is a very significant threat to commercial banana production worldwide.”
More than 99% of all bananas exported worldwide are of the Cavendish variety and they are all essentially clones of the one plant. This means there is very little genetic variation between plants and it leaves plantations highly susceptible to disease outbreaks.
The global banana industry has already been wiped out once before with a previous variety of Panama disease. Until the 1950s the Gros Michel banana was the dominant banana species, but was replaced with the Cavendish, which was resistant to the earlier variety of the fungus.
The world-first trial was conducted in heavily disease-infested soil outside Humpty Doo in the Northern Territory.
A new five-year trial will take place with the aim of growing 9,000 plants to quantify crop yields of the genetically modified banana lines. “The aim is to select the best Grand Nain line and the best Williams line to take through to commercial release,” Dale said.
The gene that was inserted into the Cavendish bananas to make them resistant has also been found in Cavendish bananas but it is not very active. The researchers have begun work trying to activate that gene in Cavendish bananas but say this will take at least four or five years.
In the meantime, the researchers say their transgenic bananas could be grown in infected areas.
“These results are very exciting because it means we have a solution that can be used for controlling this disease,” Dale said. “We have a Cavendish banana that is resistant to this fungus that could be deployed, after deregulation, for growing in soils that have been infested with TR4.”
Banana growers in Asia have largely been forced to look on helplessly as TR4 spreads, destroying their plantations.
The disease advanced into the Northern Territory about a decade ago. It has also been found in one commercial banana farm in Queensland but has so far been contained there.
The pathogen, which attacks the roots of plants and effectively tricks them into starving themselves to death while leaving the fruit otherwise unblemished, cannot be eliminated from soil that contains it.
The aim of other trials in Asia have involved mixed attempts to find resistant strains of commercial banana crops, which consist almost uniformly the world over of the vulnerable Cavendish variety.