Azole resistance is related to overexpression of the CYP51 gene in Mycosphaerella fijiensis

PO-07 Azole resistance is related to overexpression of the CYP51 gene in Mycosphaerella fijiensis Caucasella Diaz-Trujillo2, Viviane Cordovez Da Cunha2, Pablo Chong1, Gert H. J. Kema2, Rafael Arango-Isaza3 , Mauricio Guzman4, Ioannis Stergiopoulos*, Pierre J.G.M. De Wit5 2Plant Research International B.V., Wageningen University and Research Centre. Wageningen, The Netherlands 1 Phytopathology Department, ESPOL-CIBE, Guayaquil, Ecuador 3Plant Biotechnology Unit, Corporacion para Investigaciones Biologicas, CIB. School of Biosciences, Universidad Nacional de Colombia 4CORBANA, La Rita, Costa Rica 5Laboratory of Phytopathology, Wageningen University, The Netherlands *current address: Vanderbilt University, USA. Mycosphaerella fijiensis causes the threatening black Sigatoka disease in bananas and plantains. Cavendish cultivars are particularly highly susceptible and disease management is mainly through the application of systemic fungicides, including azoles. However, as expected, their intensive use has favoured the appearance of resistant strains. Previous studies showed several point mutations in the CYP51 gene close to the putative substrate-binding site that were correlated with resistance to cyproconazole and propiconazole. In the present study we found that strains with very significant resistance phenotypes to azoles have two or more insertions of a 19 bp repeat unit in the promoter region of the CYP51gene. qRT-PCR analysis revealed that increasing numbers of repeat units drive the overexpression of the CYP51 gene. We then developed a PCR-based assay to screen field populations for the presence of the repeat unit. The data show that the number of repeats in the promoter and the presence of mutations in the coding region of the CYP51 gene are clearly related to reduced azole sensitivity in M. fijiensis. We are currently developing promoter- and gene-swaps mutants of sensitive and resistant isolates to confirm this. These studies will provide important information to optimize azole management for black Sigatoka control.