Assessment of susceptibility to European stone fruit yellows phytoplasma of new plum variety and of five rootstock/plum variety combinations.

During five years two trials were carried out to assess the plum susceptibility to infection by European stone fruit yellows phytoplasmas. One trial was carried out on commercial varieties /cultivars and new selections grafted on Myrabolan 29C. Plants were evaluated in more than one plot of four plants. Yearly monitoring by visual inspection and PCR/RFLP identification of phytoplasmas allowed verifying an increasing phytoplasma presence in both symptomatic and asymptomatic plants. Eight selections from Japanese plums showed ESFY symptoms or pathogen presence in the 50% of plants and nine selections showed 20% of infection. Only nine selections showed absence of both symptoms and pathogen. Although the European selections/cultivars were not symptomatic, plants belonging to six cultivars were positive to phytoplasma presence. The scond trial was carried out to evaluate cultivar/rootstock combinations; phytoplasma symptoms and presence were observed from the first year after plantation. Two of the rootstocks appeared to induce a delay in symptoms appearance and cultivar T.C. Sun was the most susceptible to the disease.