PHYTOPLASMA DISEASES OF PRUNUS SPECIES IN EUROPE ARE CAUSED BY GENETICALLY SIMILAR ORGANISMS

Samples collected in France, Germany, Italy, Spain, and Hungary from a pricots affected by apricot chlorotic leaf roll, Japanese plums affect ed by plum leptonecrosis, and peaches, almonds and flowering cherries (Prunus serrulata) showing yellowing and decline symptoms were examine d by Southern blot analysis using cloned chromosomal DNA fragments fro m four different phytoplasmas as probes. Phytoplasma strains of Molier es disease and a disease of plum rootstock GF 8-1 were included in thi s study as were field-collected Prunus isolates from USA showing weste rn X-disease symptoms. All European samples examined hybridized with t wo probes from apple proliferation (AP) phytoplasma, with most samples showing a similar restriction pattern that was different from the pat terns of the AP phytoplasma. Restriction fragment length polymorphisms were observed in only a few of the Prunus samples tested. The AP prob es did not or only weakly hybridize to isolates of the western X-disea se phytoplasma or to European stone fruit strains that have been trans mitted to periwinkle but which were not found in diseased trees. Probe s from western X-disease and vaccinium witches' broom phytoplasmas, an d a periwinkle-maintained stone fruit strain did not or only weakly hy bridize to DNA from the field-collected European stone fruit samples. However, they did hybridize to western X-phytoplasma samples and/or th e periwinkle-maintained European stone fruit strains. It can be conclu ded that the diseases of Prunus species in Europe are induced by a rel atively uniform organism for which the name European stone fruit yello ws (ESFY) phytoplasma is proposed. This organism is distinctly differe nt from the X-disease phytoplasma and the periwinkle-maintained Europe an stone fruit strains.