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

Molecular analyses carried out either on the pear varieties ‘Conference’, ‘Comice’ and ‘William’ grafted on different rootstocks or on sixty-eight apricot varieties grafted on Myrobalan, showed the susceptibility of the tested combinations to 'Candidatus Phytoplasma pyri', transmitted by Cacopsylla pyri, and to 'Candidatus Phytoplasma prunorum', transmitted by Empoasca decedens, respectively. In order to find pear and/or apricot combinations immune to the associated Phytoplasma, several varieties grafted on new rootstock were tested in the period 2002-2008. 68 pear plants belonging to seven variety/rootstock combinations and 76 apricot plants belonging to seven combinations, all cultivated in pot, in greenhouse covered by anti-aphid tissue, were grafted with patches of infected tissues containing the specific phytoplasmas. Young healthy potted plants belonging to the pear combination ‘Comice’/P. communis and to the apricot combination ‘Palummella’/Myrobalan, both susceptible in open field to the associated phytoplasmas transmitted by the specific vectors, were also used and patch-grafted. Molecular analyses, carried out on nucleic acids extracted from leaf samples, to detect the presence of the pathogens, showed the pear variety ‘William’ grafted on Pyrus betulaefolia to be susceptible to 'Candidatus Phytoplasma pyri’. Neither the pear combination ‘Comice’/P. communis nor the apricot ‘Palummella’/Myrobalan 29 C, susceptible, in open field, to the associated phytoplasmas, became infected after patchgrafting under greenhouse conditions. Thus the results show that patch-grafting cannot be utilized in young potted plants for artificial transmission of these two phytoplasmas.Keywords: Phytoplasmas, source of immunity, variety/rootstock combination, molecular tests, insect proof green-hous