European stone fruit yellows phytoplasma is the cause of several yellows and decline diseases of stone fruits in Southern Italy
Phytoplasmas can induce several diseases of stone fruits in Europe, some of these disorders have been described as: apricot chlorotic leaf roll (EPPO A2 quarantine pest), peach vein clearing, plum leptonecrosis, decline of Japanese plum (Prunus salicina), peach yellows, peach decline, peach rosette (disease found in Italy, EPPO RS 95/212, but which may be different from the disease in USA), nectarine chlorotic leaf roll, Molière disease of sweet cherry and European plum, and other diseases affecting almond and flowering cherry (P. serrulata). Recently, with DNA-based techniques, it has been possible to detect, differentiate and characterize phytoplasmas associated with diseases. It appears that in Europe, all known phytoplasma diseases of stone fruits are caused by a relatively homogeneous organism which was called European stone fruit yellows (EPPO RS 96/003). This phytoplasma is closely related to apple proliferation, pear decline and a few other phytoplasmas of the apple proliferation group. But it is different from several European stone fruit-derived phytoplasmas which were transmitted to periwinkle, and also different from peach X-disease phytoplasma (EPPO A1 quarantine pest) which is a major pathogen in North America.
PCR and RFLP methods were used to study the etiology of peach, apricot and Japanese plum phytoplasma diseases in Campania, south of Italy. Symptoms observed on apricot and plum resembled those due to apricot chlorotic leaf roll phytoplasma (EPPO A2 quarantine pest) and plum leptonecrosis phytoplasma, whereas symptoms observed on peach were very similar to those of California peach yellow leaf roll, a disease which is absent from Europe. These symptoms include a considerable enlargement of midribs and lateral veins, the presence of light corky tissue along swollen veins which then turns dark brown. Leaf margins are rolled longitudinally upward, whereas leaf tips curl downward. Reddening of the leaves, premature leaf drop and decline of the trees is also observed. The results showed that in the majority of symptomatic trees (peach, apricot and Japanese plum), the European stone fruit yellows phytoplasma was detected. On peach trees, the peach yellow leaf roll phytoplasma was not identified. However, the authors stressed that before final conclusions can be drawn, the result of inoculation experiments of the European stone fruit yellows phytoplasma, particularly on peach, have to be obtained.