Inheritance of resistance to carboxylic acid amide (CAA) fungicides in Plasmopara viticola

Abstract

Mandipropamid is a new mandelic acid amide fungicide expressing high activity against foliar infecting oomycetes, including the grapevine downy mildew, Plasmopara viticola . Because cross-resistance with the valinamide fungicides iprovalicarb and benthiavalicarb and the cinnamic acid amide fungicides dimethomorph and flumorph was postulated, all five compounds are classified as carboxylic acid amide (CAA) fungicides. To support this classification, cross-resistance among these compounds with field isolates and the segregation of resistance in F 1 and F 2 progeny of P. viticola were evaluated. A bimodal distribution of sensitivity in field isolates and cross-resistance among all CAAs for the vast majority of isolates were detected. Crosses between sensitive (s) and CAA-resistant (r) isolates of opposite mating types, P1 and P2, yielded abundant oospores. All F 1 -progeny isolates were sensitive to CAAs (s:r segregation 1:0), whereas in F 2 progeny segregation of about 9:1 (s:r) was observed suggesting that resistance to CAA fungicides is controlled by two recessive nuclear genes. Mating type segregated in a ratio P1:P2 of c . 2:1 in F 1 and 1:1 in F 2 progeny. In the same crosses, resistance to the phenylamide fungicide mefenoxam segregated in a ratio of c . 1:3:2 (sensitive:intermediate:resistant), reflecting the monogenic, semidominant nature of resistance. The risk of resistance in P. viticola was classified as high for phenylamide and moderate for CAA fungicides. This is the first report on the inheritance of phenotypic traits in P. viticola .

Fungicide modes of action and resistance in downy mildews

“…After 14 days of incubation, plenty of oospores were produced in the leaves which were further incubated in dry conditions in the dark for another 8 weeks. Then, the rotted leaves with oospores were ground to powder, mixed with perlite and moistened with water for inducing oospore germination (Gisi et al 2007b) as originally described for P. infestans (Rubin and Cohen 2006). Young grape leaves were incubated on top of the oospore/perlite mixture for 1 to 3 weeks until first sporangiophores appeared which were picked and propagated for producing F1 progeny isolates.…”

Detection of downy and powdery mildew resistance QTL in a ‘Regent’ × ‘RedGlobe’ population

“…Despite various studies aimed at better prediction of infection based on climatic conditions, these control measures are still costly and impact negatively on the environment. Additionally, the emergence of fungicide resistant or insensitive strains of P. viticola (Gisi 2002;Gisi et al 2007) and E. necator (Erickson and Wilcox 1997;Savocchia et al 2004;Baudoin et al 2008;Furuya et al 2010) emphasize the importance of durable host resistance. Genetic host resistance to both these pathogens are available in various cultivars, but these cultivars are mainly derived from non-vinifera species and resistance varies from complete resistance to partial resistance (Wang et al 1995;Cadle-Davidson 2008).…”

Differences in the efficacy of carboxylic acid amide fungicides against less sensitive strains of Plasmopara viticola

“…3 CAA resistance is inherited in a recessive manner. 4 The aim of this report is to present differences in the response of CAA-resistant P. viticola strains towards different CAAs. Samples were collected from different Italian vineyards and tested for their sensitivity towards dimethomorph and mandipropamid.…”