Activity of Azole Fungicides and ABC Transporter Modulators on Mycosphaerella graminicola

The antimicrobialactivit y of the azole fungicides cyproconazole and propiconazole as single active ingredients and in mixtures with the ATP-Binding Cassette (ABC) transporter modulators rhodamine 6G, quercetin, quinidine, and verapamiland the strobilurin kresoxim- methylwas assessed against the wheat pathogen Mycosphaerella graminicola. Interactions amongst these compounds were evaluated on germination and germ tube growth of pycnidiospores using the Colby and Wadley method. Water agar proved to be the best test medium since all pycnidiospores germinated within 24 h of incubation and apicalgerm tube growth dominated over bud formation by intermediate cells. Analysis with the Colby method revealed that interactions between the compounds in all mixtures tested on germination of pycnidiospores were additive. With regard to germ tube growth, mixtures of cyproconazole and verapamil or kresoxim-methyldispl ayed a synergistic interaction. Analysis of mixtures of cyproconazole and kresoximmethyl with the Wadley method revealed that the interaction between the two compounds was purely additive. These results indicate that the Colby method overestimated the interaction between these two compounds in a mixture