INFECTIONS OF CANDIDATUS PHYTOPLASMA ULMI IN ULMUS PARVIFOLIA, ULMUS sp. AND ZELKOVA SERRATA TRAINED AS BONSAIS

Abstract

Ulmus L. and Zelkova Spach are two species of the family Ulmaceae occuring in Europe. Ulmus (elm) comprises about 45 species that show a range of susceptibilities to Elm Yellows (EY), the most widespread and serious phytoplasma disease for these hosts. Japanese elm (Zelkova spp.) is known for its resistance to a wide range of diseases and pests, although Zelkova Yellows (ZY) has recently been reported on Z. serrata. Since June 2006, we have carried out surveys to identify the causal agent of the decline of Ulmus spp. and Z. serrata in the Marche Region of Italy. Twenty-five leaf samples were collected from pre-bonsai and bonsai elms (U. parvifolia and Ulmus sp.), and Z. serrata, either symptomless or showing typical EY symptoms, and these were analysed by nested-PCR and RFLP based on the phytoplasma 16S rRNA gene. These analyses detected a single infection of ‘Candidatus Phytoplasma ulmi’ (16SrV-A) in all of the symptomatic leaf samples. Sequence analysis revealed 99% nucleotide homology with the EY reference strain EY-627 (Genbank accession no. AY197658). This appears to be the first report of ‘Ca. Phytoplasma ulmi’ associated with EY in Ulmus spp. and Z. serrata that have been trained as bonsais.