Brittle Leaf Disease (BLD) of date palm, of unknown etiology yet, has assumed epidemic proportions since the 1980's in Tunisia and recently in Algeria and Lybia. A search for the presence of phytoplasma, viroids and viruses, possibly involved in the disease was conducted. Seventy-five samples (leaves\fronds) were collected from symptomatic (25) and asymptomatic (50) date palms (June-July 2019) of three different orchards with trees affected with BLD in Tozeur region (South of Tunisia). RT-PCR assays performed on these samples, using degenerate- and species-specific primers for viruses and viroids detection, respectively, showed no infections with these pathogens. The search for phytoplasma using Nested-PCR assays showed that only 6 symptomatic trees (out of 25 tested, i.e. 8%) were infected, whose sequencing analyses of their PCR amplicons in BALSTn showed 99.
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44% of similarity with the Candidatus phytoplasma solani (Ca. P. solani 16SrXII-A, stolbur group). RFLP and in-silico characterization of this phytoplasma clone (33-5) showed that it deals with a new subgroup. The discovery of Ca. P. solani for the first time in the date palm, together with its’ new subgroup, makes the novelty of this investigation. More studies are needed to determine the etiology of the BLD in Tunisia, although the finding of the Ca. P. solani in six symptomatic palms is intriguing at the etiological level.
