EFFECTIVENESS DIFFERENCES OF CARBOXYLIC ACID AMIDES FUNGICIDES TOWARDS PLASMOPARA VITICOLA POPULATIONS: IN VIVO TESTS AND MOLECULAR STUDIES ON PVCESA3 GENE

Plasmopara viticola is controlled by fungicides with different modes of action,including carboxylic acid amides (CAAs). Dimethomorph was the first CAA introduced in 1988, followed by iprovalicarb, flumorph, benthiavalicarb, mandipropamid, valifenalate and latest pyrimorph in 2010 . The mode of action of CAAs is linked to the inhibition of cellulose synthesis in the Oomycete plant pathogens. The mutations conferring CAA resistance in Plasmopara viticola located on the CesA3 gene are G1105S and G1105V.The aim of this work was to evaluate the activity of dimethomorph and mandipropamid on P. viticola populations. Bioassays on leaf discs, and on seedlings were carried out. In leaf discs assay, CAAs tested on Italian populations showed different level of activity and in particular dimethomorph showed lower levels of EC95 and this behavior was also confirmed from seedling tests. All CAA resistant populations carried the G1105S/V mutations, which were detected by RFLPPCR and qPCR . In order to gain a better understanding of the different behavior and to define the possible different resistant mechanism, molecular modelling and docking studies are ongoing.