Results of patch-grafting of tissue infected by ‘Candidatus Phytoplasma pyri’ or by ‘Candidatus phytoplasma prunorum’, respectively on pear and apricot plants cultivated in pot.

Analyses carried out on pear varieties Conference, Comice and William and sixty-eight apricot varieties, grafted in open field on different rootstocks, showed their susceptibility to 'Candidatus Phytoplasma pyri', transmitted by Cacopsylla pyri, and to 'Candidatus Phytoplasma prunorum' infection, caused by Empoasca decedens, respectively. In order to find a source of immunity to ‘Ca. P. pyri’ and to ‘Ca. P. prunorum’ new different variety/rootstock combinations of pear and apricot were tested in the period 2002-2008. All the plants, cultivated in pot and covered by anti-aphid tissue under greenhouse conditions, were patch-grafted by infected tissues containing the specific phytoplasmas. The plants belong to seven variety/rootstock combinations for pear and seven combinations for apricot. Young healthy potted plants belonging to the pear combination Comice/P. communis and to the apricot combination Palummella/Myrobolan, both susceptible in open field to the associated phytoplasmas transmitted by the specific vectors, were also used and patch-grafted. Molecular analyses carried out by PCR/RFLP analyses on leaf samples to detect the presence of the pathogens showed that the only susceptible combination was William/Pyrus betulaefolia. Neither the pear combination Comice/P. communis nor the apricot Palummella/Myrobalan 29 C, susceptible to phytoplasmas in open field, become infected after patch-grafting under greenhouse. Thus the results showed that patch-grafting cannot be utilized in young potted plants for artificial transmission of these two phytoplasmas.