Scientists have highlighted the threat of fungicide-resistant strains that are causing disease-control issues worldwide.
In an effort to fight back, the team from Wageningen University in the Netherlands and the University of California, Davis have sequenced the DNA code of one of the disease-causing fungi, Pseudocercospora fijiensis or Black Sigatoka.
The collaboration’s findings are of value to the banana industry worth an estimated €7.1 bn ($8 bn) a year.
According to the Food and Agriculture Organisation of the United Nations, India and China top the table in world banana production, producing around 26% of the worldwide crop of 139 million metric tonnes.
By far the most important banana species is the Cavendish accounting for the majority of banana exports. Cavendish are resistant to Panama Disease but lack resistance from Black Sigatoka.
Fungal disease trio
In the experiment, the fungal strain P. fijiensis was first sequenced and assembled.
During the process two closely related members of the Sigatoka disease complex, P. eumusae and P. musae, were also mapped.
Further analyses of molecular markers contained within the P. fijiensis showed a high genetic diversity suggesting strong genetic selection with limited gene transfer from one population to another.
Frequencies of fungicide resistance in fungicide-treated plantations were found to be much higher than those in untreated wild-type P. fijiensis populations.
“Black Sigatoka has a huge social, ecological and economic impact worldwide and 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,” said Gert Kema, Professor in Tropical Phytopathology at Wageningen University, and study author.
The Sigatoka complex’s three fungal diseases, P. musae (yellow Sigatoka), P. eumusae (eumusae leaf spot) and P. figiensis (Black Sigatoka), together create a disease threat that requires farmers to make 50 fungicide applications to their banana crops each year to control the disease.
Mechanism of action
The study found that these fungi’s action involved shutting down the plant’s immune system as well as adapting the metabolism of the fungi to match that of the host plants.
As a result, the attacking fungi were able to produce enzymes that destroy the plant’s cell walls allowing it to feed on the plant’s sugars and other carbohydrates.
“This change in metabolism of the pathogen and the host plant may represent a ‘molecular fingerprint’ of the adaption process,” added Ioannis Stergiopoulos, plant pathologist at the University of California, Davis and co-lead study author. “It is really a wake-up call to the research community to look at similar mechanisms between pathogens and their plant hosts.”
Preventing Black Sigatoka spread is thought to contribute to the massive costs involved in global banana production. Fungicide treatments alone represent more than 35% of total production costs.
Infection with P. fijiensis not only results in crop losses but indirect costs are also incurred through inducing the early ripening of the fruit. These cost make this solution less than ideal for the export trade and the retail sector.
Source: PLOS Genetics
Published online ahead of print, doi.org/10.1371/journal.pgen.1005876
“Combating a Global Threat to a Clonal Crop: Banana Black Sigatoka Pathogen Pseudocercospora fijiensis (Synonym Mycosphaerella fijiensis) Genomes Reveal Clues for Disease Control.”
Authors: Gert Kema et al.