Asymmetrasca decedens (Cicadellidae, Typhlocybinae), a natural vector of ‘Candidatus Phytoplasma phoenicium’

Abstract

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.

‘Candidatus Phytoplasma phoenicium’ associated with almond witches’-broom disease: from draft genome to genetic diversity among strain populations

“…Intriguingly, these preliminary data seem to indicate that AlmWB phytoplasma strains identified in peach plants are distinct from strains infecting almond and nectarine based on molecular markers within the inmp nucleotide sequences. Recently, insect species of the families Cicadellidae and Cixiidae have been reported to be capable of transmitting AlmWB phytoplasma [ 56 , 57 ]. Considering this evidence, it is reasonable to hypothesize the possible implication of inmp diversity on multiple vector-specific epidemiological cycles of AlmWB phytoplasma in the diverse plant hosts.…”

A cixiid survey for natural potential vectors of ‘Candidatus Phytoplasma phoenicium’ in Lebanon and preliminary transmission trials

“…It is not always easy and different sampling techniques should often be combined, due to the different life cycle of the insects. Recently, the leafhopper A. decedens was reported as a vector of AlmWB phytoplasma within or to nearby stone fruit orchards (Abou‐Jawdah et al, ). Moreover, the presence of the disease over distantly located regions, and the detection of AlmWB phytoplasma in other insect species (Dakhil et al, ) represent a hypothesis that other potential vectors for AlmWB phytoplasma may be present.…”

“…On the other hand the recent finding concerning the possible role of A. decedens as vector of ‘ Ca . Phytoplasma phoenicium’ (Abou‐Jawdah et al, ) could explain the epidemic spread of the AlmWB disease inside almond orchards. To corroborate and confirm this theory, new surveys are required to better understand the real phytoplasma reservoirs and the biological cycle of the vector(s) with special attention to its/their host plants.…”

“…In nature phytoplasmas are mainly transmitted by sap‐sucking insects, mainly Hemiptera Auchenorrhyncha (families Cicadellidae and Cixiidae) and Sternorrhyncha (Psyllidae) (Weber & Maixner, ; Weintraub & Beanland, ). Recent study showed that the leafhopper Asymmetrasca decedens Paoli plays a major role in spreading the disease within or to nearby stone fruit orchards (Abou‐Jawdah et al, ). Moreover, the presence of the disease over distantly located regions, and the detection of AlmWB phytoplasma in other insect species (Dakhil et al ., ) may indirectly represent a hypothesis that other potential vectors for AlmWB phytoplasma may be present.…”

Differentiation and Classification of Phytoplasmas Associated with Almond and GF‐677 Witches'‐Broom Diseases using rRNA and rp Genes

“…P. phoenicium’ in Lebanon (Abou‐Jawdah et al. ), but it is not known whether it also transmits ‘ Ca . P. phoenicium’ to GF‐677 trees or whether another vector is responsible.…”