QUT researchers develop disease-resistant bananas

Monday, 20 November, 2017

Cavendish bananas are increasingly falling victim to the soilborne fungus Fusarium wilt tropical race 4 (TR4), also known as Panama disease. With about 400 million people worldwide relying on the nutrients and fibres from these fruits, researchers from Queensland University of Technology (QUT) recognised the need to address the fact that no acceptable resistant replacement has been identified.

Led by Distinguished Professor James Dale from QUT’s Centre for Tropical Crops and Biocommodities, a team of researchers conducted a field trial between 2012 and 2015 in which they developed and grew genetically modified bananas that were resistant to TR4.

“TR4 can remain in the soil for more than 40 years and there is no effective chemical control for it,” said Dale.“ 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.”

Using the RGA2 gene from the TR4-resistant wild, Southeast Asian banana subspecies Musa acuminata ssp malaccensis, the Cavendish Grand Nain bananas were grown on a commercial banana plantation outside Humpty Doo in the Northern Territory in soil heavily infested with TR4.

Over the three years, the study found one modified Cavendish line (RGA2-3) remained TR4-free while three other lines modified with RGA2 had less than 20% of plants exhibiting disease symptoms. This suggests the modified bananas developed some form of resistance against TR4, especially when compared to the 67–100% of control banana plants — including variant 218, which was supposedly tolerant to TR4 — that were either dead or TR4-infected after the three years.

Published in Nature Communications, the results also showed one of the nine lines of Cavendish Grand Nain modified with the nematode-derived Ced9 gene remained TR4-free. Researchers found no notable difference between the transgenic bananas and healthy control Cavendish.

“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.”

During the study, researchers also found a correlation between the RGA2 gene activity and TR4 resistance. Since the RGA2 gene is naturally occurring but not very active in Cavendish bananas, this encouraged further research into the possibilities of boosting natural resistance to TR4.

“We are aiming to find a way to switch that gene on in the Cavendish through gene editing,” said Dale. “We’ve started that project. It is not easy, it’s a complex process that is a way off, with four or five years of lab work.

“We’re also looking at as many genes as possible in the wild banana and screening them to identify other resistance genes, not only for resistance to TR4 but to other diseases.”

Cavendish bananas account for 40% of global banana production, and Dale hopes that investigation into ‘turning on’ the resistant genes could help protect global exports that are currently valued at about $15.8 billion.

The team have started an expanded field trial on the same plantation, growing the four RGA2 lines that showed resistance in the previous trial as well as newly developed lines of modified Cavendish Grand Nain and Williams cultivars. They will have the capacity to grow up to 9000 plants and quantify crop yield over the five years.

“The aim is to select the best Grand Nain line and the best Williams line to take through to commercial release,” Dale said. “While in Australia we primarily grow Williams, in other parts of the world Grand Nain is very popular.”

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