Molecular characterization of a phytoplasma from the aster yellows (16SrI) group naturally infecting Populus nigra L. ‘Italica’ trees in Croatia

Abstract

SummaryLeaf and branch samples were collected from 10 Populus nigra L. ‘Italica’ trees found in the Zagreb urban area. One of the P. nigra L. ‘Italica’ trees exhibited leaf yellowing, overall sparse foliage, stunting and decline. Two methods for the nucleic acid extraction in the phytoplasma detection from P. nigra were compared. A phytoplasma from the aster yellows group (16SrI) was detected by PCR in the symptomatic as well as in four apparently asymptomatic plants. The pathogens are classified, by restriction fragment length polymorphism (RFLP) analysis of the 16S rRNA gene plus the spacer region, as members of a newly described subgroup 16SrI‐P. Phylogenetic analysis of 16S ribosomal and spacer region sequence confirmed their close relationship with the other members of the aster yellows group. However, RFLP analyses of other conserved genes such as tuf, BB88 and ribosomal protein rpL22 gene, clearly confirmed that this is a molecularly distinguishable phytoplasma belonging to a new ribosomal protein subgroup designated rp‐O.