Flavescence dorée is a severe disease affecting grapevines which is caused by a phytoplasma (FDp). After extensive surveys in vineyards and experiments in controlled conditions, it was shown that differential susceptibilities to FD exist among grape varieties, such as Cabernet Sauvignon (highly susceptible) and Merlot (less susceptible). The objective of this study is to investigate the relative gene expression in response to FDp infection in CS and M under controlled conditions, and to identify genes or pathways associated with higher resistance to FD. Using high-throughput qPCR targeting defense genes, the study showed significant differences in gene expression between infected and healthy plants, and between highly and poorly susceptible plants, revealing the role of specific genes in plant defense. These preliminary results provide new insights into the mechanisms underlying the contrasting FD susceptibility in grapes, and lay the foundation for further research.