Detection of an elm yellows-related phytoplasma in eucalyptus trees affected by little-leaf disease in Italy

Eucalyptus trees showing yellowing and decline in central and southern Italy were examined for phytoplasmal infection using fluorescence microscopy (DAPI test) and polymerase chain reaction (PCR) assays. Neither the DAPI test nor direct PCR using universal and group-specific phytoplasma primers detected phytoplasmas. However, when the products obtained in the initial amplification were reamplified with universal or group-specific nested primers, phytoplasmal DNA was detected in about half of the trees. Restriction patterns of the PCR-amplified ribosomal DNA and use of specific primers indicated that the eucalyptus trees were infected by a phytoplasma of the elm yellows group. The name eucalyptus little-leaf (ELL) phytoplasma is proposed for the causal agent. The phytoplasma-infected trees differed from the trees that tested negatively by the expression of little-leaf symptoms and witches'-brooms, which are both typical of the phytoplasma-induced little-leaf diseases of eucalyptus reported from Asia and the Sudan.