Banana farming is threatened worldwide by the dreaded Fusarium wilt disease. The disease results from a fungus that causes banana plants to wither and die. A study led by professor Martijn Rep of the University of Amsterdam has now uncovered a potential Achilles heel of the fungus.
The bananas in our supermarkets have not always looked like they do now. Up until the middle of last century, bananas were smaller, thicker, and supposedly tastier. Then the infamous Fusarium wilt disease (also called "Panama disease") struck, caused by the fungus Fusarium oxysporum. Our old banana, the Gros Michel, was very sensitive to this fungus. Worldwide, banana plantations transformed into rotting fields, and for a while it looked like we had to say goodbye to the popular fruit.
The rescue came in the form of a banana variety called Cavendish. This longer, thinner, and somewhat more mealy tasting banana was not sensitive to the infamous fungus. All commercially grown bananas today are clones of that one wilt-resistant Cavendish plant. But in the 80s a new variety of the fungus appeared in Asia, "tropical race 4" or TR4. This variety of Fusarium does kill Cavendish bananas. Despite attempts to stop it in its tracks, it fungus has since spread to Africa and the Middle East. And because all Cavendish bananas are clones of each other, and therefore all susceptible to the new fungus, it poses a major threat to all commercial banana plantations.
Biologists are therefore trying to find out more about the fungus and why banana plants are or are not susceptible. An international team led by professor Gert Kema of Wageningen University has received a grant from the Royal Netherlands Academy of Arts and Sciences (KNAW) to study the topic. As part of this team, the research group of professor Martijn Rep of the University of Amsterdam recently made an important discovery: they have identified a protein and the associated gene that makes the banana fungus so aggressive. Their results were published on October 22 in the journal Plos One.
'We came up with this idea thanks to a related fungal disease in tomato', says Rep. 'In the tomato fungus a protein called Six1 contributes to its virulence. Without this protein the fungus is not nearly as aggressive. We found a very similar protein in the banana fungus. So then we investigated whether this protein is essential for the fungus to cause wilt in bananas. "
The team did a trial in which a number of banana plants were infected with the usual TR4 version of the banana fungus, and other plants with a version of the fungus in in which the gene Six1a was inactivated. Banana plants from the first group became ill, as usual. But plants that were contaminated with the modified fungus showed little disease. ‘With this we have found a possible Achilles heel of the fungus,', says Rep. ‘We can now start looking for a banana variant that is able to “recognize” this fungal protein, and is therefore immune to the disease. Just like what had been done with tomato plants. '
In the fight against Fusarium wilt, some researchers are thinking in other directions. For example, researchers in Australia have developed a genetically modified banana plant that is insensitive to the fungus. Rep: 'It is always good to try different approaches. In the fight against diseases like this one you can either try to improve the plants, or tackle the agent that causes the disease itself. By using multiple approaches we can hopefully save our current bananas from extinction.’