Wild plants could play a role in the spread of diseases associated with phytoplasmas of pigeon pea witches'-broom group (16SrIX)

Phytoplasmas are cell wall-less prokaryotic parasites associated with diseases affecting hundreds of plant species. In the Middle East, phytoplasmas of taxonomic subgroups 16SrIX-B and -C are the etiological agents of important diseases of almond and sesame, and are transmitted from plant-to-plant by leafhoppers and planthoppers. In the present study, surveys on wild plants as reservoirs of 16SrIX phytoplasmas have been carried out in North and South Lebanon. During field surveys, leaf samples were collected from 261 wild plants belonging to 41 species within 25 families. PCR-based analyses allowed the detection of 16SrIX phytoplasmas in the leaf samples of 24 plants belonging to 12 species. Eight of such species have been reported as phytoplasma hosts for the first time. Molecular characterization by nucleotide sequence analysis of 16S rRNA and rplV-rpsC genes revealed that the infected wild plant species harbored 16SrIX-C phytoplasma strains genetically undistinguishable. In silico enzymatic digestion of 16S rDNA sequences of phytoplasma strains, described in previous works, allowed the recognition of two new tentative subgroups (16SrIX-G and -H) within group 16SrIX. Results of the present study highlighted the wide host range of 16SrIX-C phytoplasma, associated with almond broomings, an almond witches’- broom-like disease in Iran, and with sesame phyllody in Iran and Turkey. The potential adaptation of 16SrIX-C phytoplasma to numerous wild plants highlights the elevated risk of its spread throughout the Middle East and neighbouring geographic regions.