Phytopathogenic Mollicutes

Twenty pear rootstock genotypes were examined for their pear decline resistance and their pomological traits in a six years field trial. All rootstock selections were grafted with the susceptible cultivar Williams followed by graft-inoculation with a severe strain of ‘Candidatus Phytoplasma pyri’ prior plantation. Seven years post inoculation all surviving trees were positive in PCR analyses. The concentration of the phytoplasmas was determined by quantitative PCR and ranged from 3x10⁶ to 6x10⁷ phytoplasma cells per gram of phloem tissue. Among the grafted rootstock genotypes clear differences in mortality, symptom expression and pomological performance were observed. Pear decline-tolerant rootstocks with promising pomological traits were selected for further evaluation.