Ex vivo expression analysis of Bd reference gene candidates. Shown is the variation in the mRNA expression (Cq) of GAPDH, TUB, R6046 and APRT in (a–c) 2 × 107 Bd spores and (d–f) 5 × 107 Bd spores that were incubated for 2 hours at 20 °C (c,f) with or (b,e) without skin tissue of midwife toads, or (a,d) a combination of both. Every condition was tested in fourfold. The whiskers represent the median, the minimum and maximum values, and the first and third quartiles. A plus (+) indicates the mean Cq value. (g) GeNorm stability analysis providing a GeNorm M and coefficient of variation (CV) value, combined with NormFinder intergroup variation analysis.