NoteDetection of 16S rDNA of ‘Candidatus Phytoplasma mali’ in plum decline in Tunisia

Abstract

‘Candidatus Phytoplasma mali’ was detected, for the first time, in plum (Prunus domestica L.) trees, with symptoms of plum decline in Tunisia. Infected trees showed leaf browning, leaf and fruit wilting followed by tree death in a few weeks. Phytoplasma was detected by polymerase chain reaction (PCR) using universal phytoplasma primer pairs P1/P7. A band with expected size was observed in samples collected from symptomatic, but not symptomless, plum trees. PCR using group-specific primers yielded a band of 1050 bp with 16SrX group specific primers fO1/rO1. Universal PCR products (1.8 kb) were used for restriction fragment length polymorphism analysis (RFLP) after digestion with endonuclease SspI. RFLP patterns obtained were similar to those previously reported for the Apple Proliferation phytoplasma (AP, 16SrX-A), the causal agent of apple proliferation disease. Blast analysis revealed that universal PCR sequences obtained from the infected Tunisian plums were identical and had the highest identity (99%) with the sequence of ‘Ca. Phytoplasma mali’. Phylogenetic analysis based on 16S rDNA gene sequences showed that the plum decline phytoplasma strain from Tunisia clustered with ‘Candidatus Phytoplasma mali’ strains. This is the first report on detection of 16S rDNA of ‘Ca. Phytoplasma mali’ in plum decline in Tunisia.