PCA based on relative phenol composition. (a) Sample score plot. Odd numbers: inoculated samples, even numbers: wounded samples. Less susceptible clones (LS; 2405, circles and 7398, squares) are coloured in yellow-red and highly susceptible clones (HS; 3178, diamonds and 3340, triangles) are coloured in green-blue. The percentages of the axes states how much of the variation the PC explain. (b) Corresponding variable loading plot. The constitutive levels of P-24 (unknown glucoside), P-52 (piceaside A/B) and P-66 (piceaside G/H) were higher in samples from less susceptible clones. Further information on phenolic numbering (P-#) is found in Additional file 3.