The trials conducted by a group of researchers at the Queensland University of Technology in Brisbane, Australia, offer promising results in the search for Cavendish banana plants resistant to Fusarium oxysporum f.sp. cubense Tropical race 4 (TR4).
The researchers designed several lines of genetically modified Cavendish bananas with resistance to this fungus and, after a 3-year field test carried out in lands heavily infested with TR4, they concluded that a Cavendish line transformed with a gene taken from a wild banana grew completely free of TR4, while three other lines showed partial resistance.
The RGA2 gene holds the key
Specifically, the team cloned the RGA2 gene from the wild progenitor of edible bananas, Musa acuminata ssp. malaccensis, which has remarkable resistance to TR4. A modified Cavendish line (RGA2-3) remained free of TR4 for the three years that the test lasted. Similarly, three other RGA2-modified lines showed strong resistance, with 20% or fewer plants exhibiting disease symptoms over a three-year period.
In contrast, 67% to 100% of the bananas used as controls were infected or severely infected by TR4 after three years; this field trial also included the Giant Cavendish somaclonal variety known as GCTCV-218, which is currently considered resistant to TR4.
A real breakthrough
The research team of Gert Kema, Professor of Tropical Plant Pathology at Wageningen University & Research, partnered on the project. "The genetically modified banana lines show that the activity of the RGA2 gene is strongly correlated with the level of resistance to TR4", he stated. “This is a breakthrough since it is the first identified resistance gene associated with the disease. However, this is only the beginning, a glimpse of light at the end of the tunnel. The next step is to deploy the immense diversity of wild bananas to diversify the fruit and establish a resilient and sustainable banana production for all," he said.
Cavendish bananas have also been found to naturally carry this RGA2 gene but it is not very active in susceptible plants. New research is studying how to 'turn on' the gene in Cavendish bananas to make them resistant to TR4.
The results have just been published in Nature Communications.