Abstract: Some biocontrol agents are known to induce systemic resistance (ISR) in plantsreducing the severity of downy mildew disease caused by Plasmopara viticola, but little isknown about the effect of temperature on this mechanism. Population genetic studies revealed aconsiderable diversity of P. viticola in vineyards. The aim of this study is to understand the effectof temperature on Trichoderma harzianum T39-induced systemic resistance on grape and tostudy the effect of temperature on populations of P. viticola. Grapevine plants treated with T39 atdifferent temperatures are inoculated with P. viticola and biological effects are evaluated. Leavesare also collected for ISR/SAR genes expression analysis. P. viticola isolates are genotyped andphenotyped (i.e. incubation time, sporulation amount). Genotypes are co-inoculated at differenttemperatures and the population is analyzed with microsatellite markers and real time PCR. Theresults will allow a better understanding of the role of the plant and the pathogen in a view ofclimate change.