Grapevine is subjected to numerous forms of pathogen aggression, especially downy and powdery mildews (Erysiphe necator and Plasmopara viticola). To develop new integrated pest management strategies and to understand the impact of alternative methods like plant defence stimulators on the evolution of bioaggressor populations, it is important to investigate the role of genetic variability and the evolution potential of pathogen populations subject to alternative method selection, in order to decrease the risk of resistant populations. The efficacy of two phosphonate derivatives (Fosetyl-Al and PK2, a foliar fertilizer) and benzothiadiazol (BTH), a salicylic acid analog, were assessed on the induction of grapevine defences against various phenotypes of grape downy mildew and various genotype groups of powdery mildews in bioassay: firstly by measuring the growth inhibition of pathogens after treatments with the different products; secondly by monitoring gene expressions coding for enzymes of phenylpropanoids (PAL, STS, CHS, CHI, LDOX, BAN), phytohormones (LOX, ACC, PAL) biosynthesis pathways and genes coding for PR proteins (CHIT4c, PGIP, PIN, GLU, PR1, PR10); and finally, by quantifying secondary metabolite production. Thus correlations between gene expression levels, efficacy and phytoalexin production were obtained.Read less <