A new resistance mechanism to DMI fungicides in the fungal banana black Sigatoka pathogen Pseudocercospora fijiensis is driven by increased expression of Pfcyp51 through …

Abstract:

Black Sigatoka is one of the most important disease in bananas and plantains and the most relevant economically. Black Sigatoka is caused by the dothideomycete fungus Pseudocercospora fijiensis, previously known as Mycosphaerella fijiensis. Disease control is mainly obtained through the application of fungicides, including the lanosterol demethylationinhibitors (DMIs). The continued use of DMI has triggered the appearance of novel genotypes, displaying reduced sensitivity to this class of fungicides. So far the phenotype of these isolates was found to be linked to the presence of non-synonymous point mutations in the target gene encoding the lanosterol 14α-demethylase enzyme (Pfcyp51). In this study, we identify a 19 base pairs (bp) repeat element in the promoter region (103 bp upstream the coding region) of the Pfcyp51gene, whose copy number correlates positively with increased resistance to DMIs. A PCR-based assay was developed to characterize four field populations of P. fijiensis in Costa Rica for the presence and copy numbers of repeated elements within the Pfcyp51 promoter. Additionally, functional analyses-including promoter swapping-showed that the presence of the repeat element proportionally upregulates Pfcyp51 expression which consequently decreases sensitivity to the DMIs in vivo. This study provides important information on the genetic mechanisms that confer reduced sensitivity to azole fungicides and might offer a tool for optimizing the use of azoles in disease management of black Sigatoka.

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