Calculation of phytoplasma titre
Phytoplasma concentration (number of copies of phytoplasma 16S rDNA gene
per µl) was calculated automatically from the quantification cycle
(Cq) values by the use of a cloned 16S rDNA gene
standard ranging from 101 to 109copies in qPCR with the internal manufacturer’s software (referred to as
estimated qPCR concentration). Samples with Cq values
higher than 30 were considered as tested negative (see Table S1; value
of control DNA from healthy trees maintained under insect-proof
conditions). Calculation of phytoplasma cells per gram wet weight of
extracted leaf tissue and phloem scrapings was performed by multiplying
the assessed qPCR concentration by the applied volume of extraction
buffer (Y) and the volume of HPLC water used for DNA resuspension, by
dividing by the number of 16S rDNA operons (2) and the wet weight of
extracted leaf tissue (X):
\begin{equation}
\text{Phytoplasma\ titer}\ \left[\frac{\text{cells}}{g}\right]=qPCR\ concentration\ \left[\frac{\text{copies}}{\text{µl}}\right]*(Y*50*\frac{1}{2}*\frac{1}{X})\ \left[\frac{\text{µl}}{g}\right]\nonumber \\
\end{equation}