Figure 3.

Traumatic resin duct (TD) formation in 2-year-old Norway spruce plants 9 weeks after application of different chemicals on the stem bark. Four weeks after application, three plants per treatment were inoculated with the fungus Endoconidiophora polonica and three plants were left intact. Upper row: cross-sectional TD area after treatment with high concentrations of oxalic acid (OxA; 200 mM), salicylic acid (SA; 500 mM) or methyl jasmonate (MeJA; 100 mM) or different concentrations of MeJA (0, 5, 25, 50 or 100 mM with 0.1% Tween 20). Control plants in the MeJA-OxA-SA experiment were untreated or were treated with 0.1% Tween 20 (n = 3 + 3 = 6). Control plants in MeJA dose-response experiment were treated with 0.1% Tween 20 (n = 3). Middle row: cross-sectional TD area relative to the total sapwood area of the current annual ring. Lower row: the number of tracheids laid down in the xylem before the TDs were formed (only plants with resin duct formation are included; n = 1-4). Bars represent treatment group means ± 95% confidence interval of the mean. Points represent individual replicates. Treatment groups that do not share the same letter are significantly different (1-way ANOVA (~ treatment) followed by Tukey post-hoc, p < 0.05).