Santos, Ricardo F.
Fraaije, Bart A.
Garrido, Lucas da R.
Monteiro-Vitorello, Claudia B.
Total Authors: 5
 Univ Sao Paulo, Dept Plant Pathol & Nematol, Luiz de Queiroz Coll Agr, BR-13418900 Piracicaba, SP - Brazil
 Natl Inst Agr Bot, Cambridge - England
 Embrapa Grape & Wine, Bento Goncalves - Brazil
 Univ Sao Paulo, Dept Genet, Luiz de Queiroz Coll Agr, Piracicaba - Brazil
Total Affiliations: 4
Web of Science Citations:
Grapevine downy mildew, caused byPlasmopara viticola, is commonly controlled by quinone outside inhibitor (QoI) and carboxylic acid amide (CAA) fungicides. QoI resistance is conferred by a mutation resulting in a G143A alteration in cytochromeb, while CAA resistance is associated with a G1105S mutation in cellulose synthase 3. The aims of this study were to (a) verify the presence of QoI and CAA resistance inP.viticolain Brazil, (b) develop a single nucleotide polymorphism (SNP) detection pyrosequencing assay for quantitative detection of G143A, and (c) determine the geographic prevalence and distribution of G143A and G1105S in Brazilian field populations.P.viticolaisolates were sampled from two vineyards reporting failures of QoI and CAA control. Their growth was unaffected by azoxystrobin and mandipropamid, and resistance was associated with the G143A and G1105S mutations, respectively. The SNP detection pyrosequencing assay developed for G143A detection was precise and accurate. Pyrosequencing assays revealed that G143A and G1105S frequencies varied among the 66 field populations and were positively correlated with the number of QoI and CAA applications, respectively. The G143A mutation was observed in 60 populations, 39 of them with frequencies over 90%. G1105S was detected in 20 populations with frequencies ranging from 18.3% to 100%, and which also carried the G143A mutation. Multiple resistance to QoI and CAA inP.viticolawas confirmed for the first time in South America. Future resistance monitoring surveys and management strategies must be adopted to prevent further increase in QoI and CAA resistance in Brazil. (AU)