Complexity of almond witches’-broom disease cycle in Lebanon

'Candidatus Phytoplasma phoenicium' (CaPphoe) is the etiological agents of almond witches’-broom (AlmWB) in Lebanon and in Iran. The aim of this study was to investigate its epidemiological cycle. During field surveys, conducted in the 4-year period 2010-2013 in AlmWB-infested almond and peach orchards and surroundings, leafhoppers (Cicadellidae) and cixiids (Cixiidae) were collected by means of yellow sticky traps, Malaise traps and mechanical aspirator. Moreover, leaf samples were collected from crops and wild plants where insects had been captured. Asymmetrasca decedens was the prevalent leafhopper, identified mainly on almond plants; Cixius sp., Tachycixius spp., Hyalesthes spp., and Eumecurus spp. were the prevalent cixiids, identified mainly on the weeds Smilax aspera L. and Anthemis sp.. CaPphoe was identified in the insects A. decedens, Cixius sp., Tachycixius spp., and Eumecurus spp., and in crops and wild plants where the insects were collected. Transmission trials demonstrated that A. decedens and Tachycixius spp. are able to transmit CaPphoe to plants. Such results revealed a complexity of AlmWB epidemiological cycle in Lebanon, involving (i) the leafhopper A. decedens, possibly responsible for the transmission of CaPphoe from almond to almond, and (ii) cixiids of the genus Tachycixius, possibly responsible for the transmission of CaPphoe from weeds to almond. For these insects, almond could be considered only dead-host for the phytoplasma. Molecular characterization of CaPphoe strains identified in the hosts will help to corroborate and confirm this picture, and to understand how CaPphoe moves to peach.