Stability indices (A), and pairwise variation to determine the optimal number of normalisation genes (B) calculated with GeNorm, and stability indices calculated with NormFinder (C). (A) and (C): The stability indices are shown for all species combined, and also barley, wheat and oats individually. The stability of gene expression is inversely proportional to the stability index, so least stable genes have the lowest achieved values and vice versa. (B): The optimal number of genes was determined separately for barley, wheat and oats as well as for all samples combined (all). The recommended cut-off value under which there is no need for inclusion of another gene is 0.15.