Potential vectors of 'Candidatus' Phytoplasma phoenicium' in Lebanon

Background and objectives The presence and rapid spread of AlmWB in Lebanon, causing serious economic losses, entails the activity of one or more insect vectors. Previous investigations focused on the family Cicadellidae showed Asymmetrasca decedens Paoli to be the most abundant species in stone fruit orchards and able to carry ‘Ca. Phytoplasma phoenicium’. Although other leafhopper species, usually present in very low density in the orchards and belonging to the subfamilies Typhlocybinae and Deltocephalinae were found positive to the phytoplasma as well, their vector ability has never been proved by transmission trials (Abou-Jawdah et al., 2003, Dakhil et al., 2011). Beside the leafhoppers some cixiid (planthopper) species are known as vectors of phytoplasmas to various crops (Maixner, 1994; Jović et al., 2007; Pinzauti et al., 2008). For this reason we focused the survey on the cixiid-fauna present in almond and nectarine orchards of Lebanon with particular attention on their natural infection by phytoplasmas. Materials and Methods Deepened samplings were carried out through the years 2010-2012 by means of Malaise and yellow sticky traps in two AlmWB infected orchards planted respectively with almond and nectarine trees. Additional direct samplings with a hand-held D-vac were performed in the same orchards and surroundings. All cixiids captured with the different methods were identified by morphological features and subsequently analysed for phytoplasma detection. Total DNA was subjected to direct and nested PCR, using respectively the semi-specific primer pair AlWF2/AlWR2 (Abou-Jawdah et al., 2003) and the primer pair P1/P7 (Deng and Hiruki, 1991; Smart et al., 1996) followed by the primers R16F2n/R16R2 (Gundersen and Lee, 1996) universal for phytoplasmas. Nested PCR products were then sequenced to identify taxonomic 16Sr group/subgroup. Results and Discussion The following cixiid genera were collected during the different insect field collections: Cixius, Tachycixius, Eumecurus, Oliarus, Pentastira, Pentastiridius and Hyalesthes. The molecular analyses pointed out Cixius, Tachycixius, Eumecurus and Hyalesthes as carriers of ‘Ca. Phytoplasma phoenicium’. These results highlighted the role of planthoppers in the epidemiology of AlmWB disease. Nevertheless further studies about their vector activity as well as their specific identification are needed. Concerning this latter a deep systematic revision is desirable to solve the taxonomic critical situation of this family. Moreover, since almost no information is known about their biology, new surveys will be important to better understand the disease spread and define suitable control strategies.