Activity of fungicides and modulators of membrane drug transporters in field strains of Botrytis cinerea displaying multidrug resistance

Abstract

In Botrytis cinerea, multidrug resistant (MDR) strains collected in French and German vine- yards were tested in vitro, at the germ-tube elongation stage, towards a wide range of fungicides. Whatever the MDR phenotype, resistance was recorded to anili- nopyrimidines, diethofencarb, iprodione, fludioxonil, tolnaftate and several respiratory inhibitors (e.g., pen- thiopyrad, pyraclostrobin). In MDR1 strains, overpro- ducing the ABC transporter BcatrB, resistance extended to carbendazim and the uncouplers fluazinam and malo- noben. In MDR2 strains, overproducing the MFS trans- porter BcmfsM2, resistance extended to cycloheximide, fenhexamid and sterol 14α-demethylation inhibitors (DMIs). MDR3 strains combined the overexpression of both transporters and exhibited the widest spectrum of cross resistance and the highest resistance levels. The four transport modulators, amitriptyline, chlorpromazine, diethylstilbestrol, and verapamil, known to affect some ABC transporters, were tested in B. cinerea. In our experimental conditions, the activity of several fungi- cides was only enhanced by verapamil. Interestingly, synergism was only recorded in MDR2 and/or MDR3 isolates treated with tolnaftate, fenhexamid, fludioxonil or pyrimethanil, suggesting that verapamil may inhibit the MFS transporter BcmfsM2. This is the first report indicating that a known modulator of ABC transporters could also block MFS transporters.