Abstract
Apple proliferation caused by ‘
Candidatus
Phytoplasma mali’ is an economically important disease of apple (
Malus
´
domestica
). The availability of a simple quantitative approach to assess pathogen load in infected host plants would certainly contribute to a better understanding of pathogenesis and epidemiology. This study proposes a quantification approach not requiring the analysis of external standard curves. It is based on the simultaneous detection of the 16S rRNA gene of the pathogen and the 1-aminocyclopropane-1-carboxylate oxidase gene of the host plant in a single-tube reaction using TaqMan chemistry. The quantity of the phytoplasma relative to its host plant is determined as the difference between C
T
values of the two target genes (ΔC
T
). To assess the agreement of the relative quantification approach with a standard curve-based method, a dataset of 450 DNA samples from infected apple trees was reanalysed. Comparison of the ΔC
T
-based relative quantities with the corresponding absolute values revealed high degrees of agreement between the relative and absolute quantification methods. The ΔC
T
procedure can thus be considered adequate for quantification of the phytoplasma in infected host plant tissue. In addition, this approach ensures improved methodological standardisation and increased analysis throughput.