Tetra-Primer ARMS PCR for rapid detection and characterization of Plasmopara viticola phenotypes resistant to carboxylic acid amide (CAA) fungicides.

BACKGROUND The occurrence of Plasmopara viticola populations resistant to carboxylic acid amide (CAA) fungicides is becoming a serious problem in the control of grapevine downy mildew worldwide. The resistance is caused by point mutations in the PvCesA3 gene. These isolates with this mutation have been detected mainly by determining the minimum inhibitory concentration of fungicides, which is always time consuming and inefficient. RESULTS To establish a suitable method for rapid detection of the G1105S mutation in P. viticola, an efficient and simple molecular method was developed, based on tetra-primer ARMS PCR. A set of four primers were designed and optimised to distinguish the different genotypes within one step. Only 2 h was required from the sampling of symptoms to the phenotyping of fungicide resistance. Using this method, CAA-resistant P. viticola were identified for the first time in China. Also, the finding of sensitive heterozygotes indicated that the resistant allele is spreading in the population in Ziyuan. CONCLUSION This new method proved to be useful as an early warning system for resistance outbreaks of P. viticola to CAA fungicides in the field and may be helpful in decisions concerning rotation of different fungicide groups. © 2016 Society of Chemical Industry