Figure 1.

Frequency of B. nigra plants expressing HR-like necrosis induced by Pieris eggs and effects of HR-like necrosis on Pieris egg survival and PR1 gene expression. (a) Percentage of HR-like necrosis on plants of a Dutch field population (Steenfarbiek) and in the greenhouse. (b) Percentage (estimated mean ± s.e.) of caterpillars emerging from Pieris eggs on plants of a Dutch field population (Steenfarbiek) (2010 and 2011, generation 1 and 2); ***p < 0.001; n.s., not significant (GLM, p > 0.05). (c) Variation in HR severity and effect on P. rapae egg survival (estimated mean ± s.e.) in the greenhouse (different severities were visually characterized as in the pictures); different letters indicate significant differences (GLM and LSD, p < 0.05). (d) Effect of HR-like necrosis induced by P. rapae eggs on expression changes (mean ± s.e.) of HR-marker gene PR1 at 24 and 72 h after oviposition; different letters indicate significant differences (ANOVA, Tukey test p < 0.05, n = 3–5 biological replicates). Numbers inside the bars represent number of plants for data of 2011 and number of eggs for data of 2010. Hypersensitive response (HR), in light grey HR−: no necrotic zone observed, in dark grey HR+: necrotic zone. (Online version in colour.)