Fungicide sensitivity of Mycosphaerella graminicola Tunisian isolates: the importance of drug transporter genes in the process of fungicide tolerance

Seventeen Mycosphaerella graminicola isolates from Tunisia and two reference isolates from Europe (St-Q7-2 and IPO323) were examined for sensitivity to azoxystrobin and tebuconazole and for the importance of the drug transporter genes MgAtr3 (ABC transporter), MgMfs1 (MFS transporter), MgSlt2 (MAP Kinase), MgGpa1 and MgGpb1 (cyclic AMP) in the process of fungicide tolerance. All Tunisian isolates were sensitive to both fungicides, but considerable variability in sensitivity, and evidence for slight multidrug resistance toward both fungicides (r = 0.58), were observed. A gene expression assay revealed that MgAtr3 and MgMfs1 are involved in tolerance to both fungicides. MgAtr3 is likely involved in tolerance to tebuconazole, while MgMfs1 is likely required for tolerance to azoxystrobin. The other genes examined were found more likely to be pathogenicity factors rather than fungicide tolerance factors, except for MgSlt2 which was weakly induced by azoxystrobin treatment. This study has indicated that the Tunisian population of M. graminicola remains more sensitive to strobilurin and azole fungicides than European populations, and reports the importance of the ABC and MFS transporters MgAtr3 and MgMfs1 in the mechanism of fungicide tolerance