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Research reveals mechanism making banana fungus less responsive to crop protection

An international team of scientists led by Wageningen University & Research has discovered a new genetic mechanism that makes the notorious Black Sigatoka fungus less sensitive to the main chemical crop protection products used against the disease. 



The discovery shines light on this increasingly reduced sensitivity and underlines the importance of developing banana varieties resistant to the fungus which causes Black Sigatoka.
 
Pseudocerospora fijiensis, the fungus causing the dreaded Black Sigatoka disease in banana cultivation, is tackled with chemicals. In practice, this requires farmers around the world to spray against the disease between 35 and 70 times a year. One specific type of fungicides, the so-called demethylase inhibitors (DMIs), form the backbone for managing the disease. Unfortunately, the fungus is becoming increasingly less sensitive to these products on a global scale. 



Dr Pablo Chong conducted his PhD research under the supervision of Gert Kema, professor in tropical phytopathology at Wageningen University & Research. The working hypothesis was that “we thought that the reduced sensitivity of the fungus was caused by changes in the protein, a demethylase enzyme, which is the target of the DMIs” Kema says. 

“As a result we only looked at mutations in the segment of the gene that encodes the enzyme. What we found is that the reduced sensitivity is also caused by changes in the promoter, the switch that controls the gene. In the promoter we discovered a segment of DNA that is concatenated up to six times. The larger the number of DNA-repeats in the promoter, the less sensitive the fungus.”



The less sensitive Black Sigatoka strains that were found in banana cultivation and studied by the team all had a combination of mutations in the encoding part of the gene as well as DNA-repeats in the promoter.

Kema: “Mutations in the coding segment of the gene reduces the ‘docking’ of the compound in the enzyme, while the DNA repeats in the promoter make the gene extra active. These two factors together appear to ensure that the fungus has so much well-functioning enzyme in its cells that it is far less affected by the crop protection. As a result, the banana plants develop disease despite the application of these products.”



The findings emphasise the importance of smart crop protection, using not only DMIs but also fungicides that function in a completely differently way. This will slow the pace of reduced sensitivity in the fungus. 
 
“The results of our research also underline the importance of developing Black Sigatoka resistant banana varieties” concludes Kema. “This is the only way to make global banana cultivation more sustainable.” 

For more information: 
Erik Toussaint
Wageningen University & Research 
Tel: +31 651 56 59 49 

Publication date: 11/22/2017


 


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