discovery shines light on this increasingly reduced sensitivity and
underlines the importance of developing banana varieties resistant to
the fungus which causes Black Sigatoka.
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.
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.
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.”
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.
“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.”
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.
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:
Wageningen University & Research
Tel: +31 651 56 59 49