Distribution of calculated PCR efficiencies as determined for two indica rice cultivars. The two distributions were compared using a Kolmogorov-Smirnov test and were found to be significantly different at p = 0.001. Non-parametric comparison of mean values (Mann-Whitney U test) confirmed the presence of statistically significant differences at p = 0.000001. Transformation to expression values revealed that the slightly different PCR efficiencies could lead to a mean difference of maximal 0.3, when the fold change was expressed as log2. Individual primer pairs can thus exhibit slight differences for their target genes in different cultivars. However, this does not significantly affect the overall applicability of the primer platform for expression profiling experiments (Caldana et al., manuscript in preparation).