Close‐up of the principal component analysis (PCA) of plant susceptibility to Aphanomyces euteiches (Fig. S2, see Supporting Information), highlighting the behaviour of the four selected genotypes cultivated in complete or nitrate‐deficient (NØ) medium. Susceptibility of the Medicago truncatula genotypes A17, F83005.5, DZA045‐6 and SA022322 under contrasting N availability (complete medium, squares; NØ medium, circles) was compared by PCA (PC1 explains 44% of the variance). The negative side of the PC1 axis is highly correlated with the genotype susceptibility to A. euteiches (ELISA, root browning and stem necrosis, see Fig. S2). Bars indicate standard error (n = 4 biological replicates). Data from a representative experiment out of three independent experiments are shown.