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A survey for phytoplasma diseases in tomato and pepper fields in Lebanon was conducted during 2003 and 2004. Tomato plants with stunting, yellowing or purplish leaves, proliferation of laterals buds, hypertrophic calyxes and virescent flowers were found in 25% of the tomato fields surveyed, where they represented 2-8% of the plants. Pepper plants displaying stunting and yellowing of leaves, were found in 27% of the fields and 1-4% of the plants were affected. Phytoplasmas infecting tomato and pepper had identical 16S-rDNA RFLP profiles and sequences. A phytoplasma isolate named PTL was transmitted by dodder from a diseased tomato plant to a periwinkle (Catharanthus roseus) plant in which it induced leaf yellowing, virescence and phyllody. 16S-rDNA phylogenetic analysis classified PTL as a strain of 'Candidatus Phytoplasma trifolii'.

Candidatus Phytoplasma phoenicium' is associated with a lethal disease of almond, peach and nectarine named almond witches'-broom disease (AlmWB). The disease spread rapidly in Lebanon from coastal areas to elevations exceeding 1200 m, killing over 150,000 trees in a span of two decades. The mode of spread suggested the involvement of efficient vector(s) and Asymmetrasca decedens (Hemiptera, Cicadellidae) was suspected as it is the most abundant leafhopper species present in Lebanese stone fruit orchards. Living A. decedens specimens were collected from fields heavily infested by AlmWB and used in transmission trials on healthy peach almond hybrid GF-677 and peach GF-305 seedlings with an inoculation-access period of 30 days. PCR analysis supported by sequencing showed that A. decedens is a carrier of the phytoplasma, and that the phytoplasma was detected in insect salivary glands and in some inoculated GF-677 and GF-305 seedlings. One year post-inoculation, 'Ca. P. phoenicium' was detected in newly emergent leaves of inoculated seedlings. However, the characteristic symptoms of witches'-broom were not observed. PCR amplified fragments from phytoplasma-positive seedlings and from A. decedens samples showed 99.9% nucleotide identity in their 16S RNA region and phylogenetic analysis using a neighbour jointing tree confirmed that the phytoplasmas detected in both insects and inoculated seedlings belonged to 16SrIX-B (D). The present manuscript is the first known report for a leafhopper vector of 'Ca. P. phoenicium' and shows that the incubation period of the disease in plants may be longer than 1 year. The importance of phytosanitary control measures, the adoption of a national strategy and regional cooperation in order to contain the further spread of the disease are discussed.

Almond witches'-broom (AlmWB) disease, associated with 'Candidatus Phytoplasma phoenicium', is an emerging threat with real risk of introduction in Euro-Mediterranean Countries. Its rapid spread over large geographical areas suggests the presence of efficient insect vector(s). In the present work, a survey on cixiids was carried out in Lebanon in the years 2010-2013 in AlmWB-infested almond and nectarine orchards. Insects were collected by means of different methods, identified with a stereo microscope, and analysed for phytoplasma identification through 16S rDNA PCR-based amplification and nucleotide sequence analyses. Preliminary transmission trials were performed with the most abundant species. A list of the cixiid genera and species present in the studied area is given as well as some information about their biology. 'Ca. Phytoplasma phoenicium' strains were detected in the genera Cixius, Tachycixius, Eumecurus and Hyalesthes. Preliminary trials revealed that Tachycixius specimens were able to transmit the detected strains to healthy peach potted seedlings. Further studies are required to better clarify the taxonomic status and the bio-ethology of collected planthoppers and deeply study their role as phytoplasma vectors.

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