Identification of new 16SrIX subgroups, -F and -G, among 'Candidatus phytoplasma phoenicium' strains infecting almond, peach and nectarine in Lebanon

Almond witches'-broom is a lethal almond disease associated with 'Candidatus Phytoplasma phoenicium', subgroups 16SrIX-B and -D. In Lebanon, where the disease was first reported, analogous diseases affecting peach and nectarine were recently associated with presence of 'Ca. P. phoenicium'. In the present study, genetic diversity among 24 'Ca. P. phoenicium' strains infecting almond, peach and nectarine plants in diverse geographic regions of Lebanon was investigated by virtual restriction fragment length polymorphism (RFLP) analysis of 16S rDNA nucleotide sequences. Calculation of virtual restriction similarity coefficients revealed the presence of two new subgroups, -F and -G, in group 16SrIX that were confirmed by real RFLP analyses. Obtained results open new opportunities for in-depth studies of the distribution of 'Ca. P. phoenicium' strains in plant hosts and insect vector populations from different geographic areas of Lebanon.