INVESTIGATIONS WITH REAL-TIME PCR ASSAY ON THE TRANSMISSIBILITY OF PEAR DECLINE PHYTOPLASMA (PDP) WITH DORMANT BUDS

Pear decline (PD) is one of the most dangerous diseases of pear trees. A study was carried out to determine the possibility of transmitting the causal agent, pear decline phytoplasma (PDP), through grafting with dormant buds collected from naturally infected trees, due to winter degeneration of the sieve tubes of the above ground part of pear trees. A real-time PCR procedure for PDP detection was set up with a multiplex assay where host and pathogen DNA could be amplified simultaneously to distinguish between uninfected plant material and false negatives due to PCR inhibition. Real-time PCR assays were performed on 92 seedlings of Pyrus communis one year after grafting with dormant buds resulted PD-positive after PCR analysis, from cvs. Abate Fetel, Conference and William, grafted on P. communis rootstocks. Ten pear seedlings were also grafted with root samples from the above mentioned trees. No phytoplasmas were detected in the 92 grafted seedlings, on the contrary 6 plants on 10 tested positive after root grafting. The results suggested that in our conditions PDP is not transmissible with dormant buds to healthy trees.