Wetenschap - 12 augustus 2016

Scientists find effector gene in banane disease (video)

tekst:
Albert Sikkema

Scientists have mapped the DNA of the pathogen of the feared Black Sigatoka disease in bananas. This will help create resistant banana species, says research team leader Gert Kema.

The fungal disease 'Black Sigatoka' is affecting more and more banana plantations around the world and is threatening the production of bananas. The fungus Pseudocercospora fijiensis attacks the leaves in such a way that it will result in a massive loss in harvest. Farmers are forced to use more and more fungicides to keep the fungus in check. In spite of this the fungus is spreading steadily from Asia to the rest of the world. There is no type of bananas which is commercially produced on a large scale which is resistant to Black Sigatoka. Having the DNA of the pathogen mapped, Kema and his colleagues are trying to find out how the fungus is infecting the banana plants, so that they can stop the infection.

Effector
The research of the DNA has given the scientists leads, they report on August 11th in the magazine PLoS Genetics. The researchers have found a section of DNA in the fungus which causes a resistance reaction in the wild banana species Calcutta 4. The DNA of the fungus produces a so called effector which is recognised by the receptor of the wilde banana, which then eliminates the fungus. The researchers hope to implement this mechanism into the DNA of the commercial banana type Cavandish.

There is another option to make a resistant banana however. Previous research showed that tomato plants can also contain the receptor, which recognises the Black Sigatoka fungus. This gene for the receptor is already known and available. The scientists can incorporate this tomato-gene inside the DNA of the banana, to develop the resistant banana plants.

Resistance
This DNA research gives us more insight in the interaction between fungus and banana plants, says research team leader Gert Kema, professor of Tropical phytopathology in Wageningen. ‘This gives us new possibilities to develop a new commercial species with a resistance to Black Sigatoka.’ Which is not only better for the economy, battling the fungus costs the industry around 400 million dollars a year, but also to the environment. Banana growers usually spray up to fifty times a year with fungicides to fight the much feared fungus.

The researchers also found that the genome Pseudocercospora fijiensis is remarkably big and contains a lot of repetitive DNA. The fungus used to be know as Mycosphaerella fijiensis. Scientists from Brazil, France, Canada, Colombia, Costa Rica, Iran, The Netherlands, the United States, United Kingdom and Switserland all collaborated on this publication.

Leaf-spot disease
The Black Sigatoka disease in the banana cultivation industry should not be confused with the Panama disease, which is caused by a different type of fungi. The Black Sigatoka is caused by a leave disease which spreads through the air, whilst the Panama disease (Tropical race 4) is caused by a soil pathogen. Black Sigatoka has a bigger environmental impact, because the leave-spot disease needs to be killed with spraying fungicides. But the Tropical Race 4 has a bigger impact on the cultivation of bananas, because soil disinfection is impossible, which means once a soil is infected, it's game over for the bananas.

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