Assessment of fungicide resistance and pathogen diversity in Erysiphe necator using quantitative real-time PCR assays.
BACKGROUND
Management of grapevine powdery mildew Erysiphe necator Schw. requires fungicide treatments such as sterol demethylation inhibitors (DMIs) or mitochondrial inhibitors (QoIs). Recently, reduction in the efficacy of DMIs or QoIs was reported in Europe and the United States. The aim of the present study was to develop real-time qPCR tools to detect and quantify several CYP51 gene variants of E. necator: (i) A versus B groups (G37A) and (ii) sensitive versus resistant to sterol demethylase inhibitor fungicides (Y136F).


RESULTS
The efficacy of the qPCR tools developed was better than the CAPS method, with a limit of 2 pg for E necator DNA, 0.06 ng for genetic group A and 1.4 ng for the DMI-resistant allele. The detection limits of qPCR protocols (LOD) ranged from 0.72 to 0.85%, and the quantification limits (LOQ) ranged from 2.4 to 2.85% for the two alleles G47A and Y136F respectively. The application of qPCR to field isolates from French vineyards showed the presence of DMI-resistant and/or QoI-resistant alleles in French pathogen populations, linked to genetic group B.


CONCLUSIONS
The real-time PCR assay developed in this study provides a potentially useful tool for efficient quantification of different alleles of interest for fungicide monitoring and for population structure of E. necator.
Dufour
Marie-Cécile
MC
INRA, UMR Santé Végétale 1065, ISVV, Villenave d'Ornon, France.
Fontaine
Séverine
S
Montarry
Josselin
J
Corio-Costet
Marie-France
MF
D000483:Alleles; D001203:Ascomycota / Q000187:drug effects* / Q000235:genetics; D025141:Drug Resistance, Fungal / Q000235:genetics*; D005659:Fungicides, Industrial / Q000494:pharmacology*; D008126:Lod Score; D010571:Pest Control; D016133:Polymerase Chain Reaction / Q000379:methods; D020641:Polymorphism, Single Nucleotide; D027843:Vitis / Q000382:microbiology*
D005659:Fungicides, Industrial