Impact of grapevine downy and powdery mildew diversity on efficacy of phosphonatederivatives (fosetyl-AL and fertilizer PK2) and salicylic acid analog (BTH)described as stimulators of plant defences

Abstract: Grapevine is subjected to numerous forms of pathogen aggression, especially downyand powdery mildews (Erysiphe necator and Plasmopara viticola). To develop new integratedpest management strategies and to understand the impact of alternative methods like plantdefence stimulators on the evolution of bioaggressor populations, it is important to investigate therole of genetic variability and the evolution potential of pathogen populations subject toalternative method selection, in order to decrease the risk of resistant populations. The efficacy oftwo 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 variousphenotypes of grape downy mildew and various genotype groups of powdery mildews inbioassay: firstly by measuring the growth inhibition of pathogens after treatments with thedifferent products; secondly by monitoring gene expressions coding for enzymes ofphenylpropanoids (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 betweengene expression levels, efficacy and phytoalexin production were obtained.