Quantitative real-time PCR of transcripts differentially expressed in resistant and susceptible trees following PWN inoculation. The putative functional genes from (a) to (h) were clearly discernible ESTs in susceptible SSH libraries. The putative functional genes from (i) to (p) were clearly discernible ESTs in resistant SSH libraries. Elongation factor 1-alpha (EF1a) was used as the reference gene, and the data were calibrated relative to the transcript levels in resistant trees prior to nematode inoculation (at 0 days). The data are presented as the mean ± S.D. of three replicates. Means designed by the same letter did not significantly differ at P < 0.05 according to Tukey's HSD test.