QT-clustering analysis obtained using the expression values of the 8,660 stress-related genes differentially expressed in at least one condition/genotype. The analysis was performed with a minimum cluster size of 30 and a correlation value of 0.80. The four treatment conditions, grouped by genotypes, are plotted on x axis. The relative expression level (for each probe set the data were normalized to the median expression level of the Ofanto Ctrl samples) is plotted on the y axis. The lines represent the mean expression trend of all probe sets belonging to each cluster. The nine clusters (cluster 1, 4, 8, 10, 17, 18, 23, 40 and 47) contain genes whose expression might be associated to the different molecular response of Ofanto and Cappelli (details in the Results). The whole data set of 52 clusters is presented in the Additional file 4.