Symptom expression and 'Candidatus Phytoplasma prunorum' concentration in different Prunus species.

A SYBR (R) Green I real-time PCR assay has been used for specific detection and quantification of Candidatus Phytoplasma prunorum' in different Prunus species such as P. armeniaca, P. salicina, P. persica and P. tomentosa grown in a screenhouse and infected by means of the vector. Infection level of 'Ca. P. prunorum' in plant samples, expressed as 'Ca. P. prunorum' GU per ng of plant DNA, was achieved by the standard curve quantification method choosing rplV (17)122) gene as target for phytoplasma quantification and plant 18S rDNA to normalize the data. Visual inspections of the plants maintained in the screenhouse and qualitative molecular data demonstrated that the species P. armeniaca and P. salicina are the most susceptible and sensitive, that P. persica is less susceptible but quite sensitive and finally that P. tomentosa is less susceptible and quite tolerant. Quantitative molecular data for the first time demonstrated, for the first time, that 'Ca. P. prunorum' titre increases during the vegetative season, and that symptom expression is correlated with its infection level.