An international consortium led by scientists from Wageningen UR (University & Research centre) has unravelled the DNA of Pseudocercospora fijiensis, the fungus that causes the much-feared black Sigatoka disease in bananas.

The findings provide leads to development a resistant banana plant. The results were published this month in PLoS Genetics.

Black Sigatoka

Banana production is threatened by various fungi. One of them, Pseudocercospora fijiensis (previously known as Mycosphaerella fijiensis), causes black Sigatoka, a worldwide air-borne fungus that affects banana-plant leaves and results in huge yield losses.

Photo: Wageningen UR

Spraying banana crops. Photo: Wageningen UR

The disease also reduces the quality of the fruit, causing premature ripening. The bananas can then no longer be exported, and growers lose their income. The Cavendish banana, the most commonly grown banana worldwide, is especially susceptible to black Sigatoka.

Farmers who can afford it use crop protection products or fungicides to manage black Sigatoka. The effectiveness of these products often quickly reduces, however, which means that most commercial plantations have to spray more than 50 times a year in many banana producing regions.

This has a major impact on the environment of the plantations and costs the banana sector $400 million a year.

DNA sequence offers possibilities for disease control

Gert Kema, professor in tropical phytopathology at Wageningen University and banana expert, led the research.

“Black Sigatoka has a huge social, ecological and economic impact worldwide,” he said. “Thanks to the sequencing of the DNA of the Pseudocercospora fungus, we are now gaining a greater insight into the interaction between the fungus and the banana plant. This provides us with leads for increasing the sustainability of banana cultivation, making it better for the environment, the local population and the economy. For example, the insights offer us opportunities to develop a banana plant that is suitable for production and export, and which is also resistant against black Sigatoka.”

This fresh understanding of the DNA of the black Sigatoka fungus is also providing new information that is useful to develop more effective and, hopefully, environmentally friendly crop protection products. This could reduce the amount of spraying, which in turn,would improve the quality of life of the people working on the plantations and those who live in the immediate surroundings.

The research has helped identify the segment of DNA of the fungus that forms the basis for a so-called effector: a substance in the fungus that generates a resistance reaction in the wild banana variety Calcutta 4. This wild banana has a receptor which recognizes the fungal substance. In other words, thanks to the receptor, the wild banana plant “knows” when it is being attacked and then encapsulates the fungus, preventing the leaves from being colonized further.

Can tomato DNA help?

The scientists also discovered that tomato plants recognize the substance of the black Sigatoka fungus via a receptor.

The wild Calcutta 4 banana and the tomato apparently resemble each other genetically in this regard. A great deal is already known about the tomato receptor, and the gene for the receptor is also available. It would be relatively simple to build these tomato genes into the DNA of a banana in the hope of developing resistant banana plants.

Financing and partners

Scientists from Brazil, Canada, Colombia, Costa Rica, France, Iran, the Netherlands, Switzerland, the UK and the USA worked together on the article.

The DNA of the fungus was sequenced by the US Department of Energy’s Joint Genome Institute and by Syngenta Biotechnology Inc. The Dutch research was co-financed by the Dioraphte Foundation, while other scientists were financed by the Colombian Administrative department of Science, Technology and Innovation; the National University of Colombia in Medellin; and from the National Council of Science and Technology (CONACyT) in Mexico.