EPPO PRA for ‘Candidatus Phytoplasma phoenicium’ (Bacteria: Acholeplasmataceae) causing almond witches’ broom
Based on this PRA, ‘Candidatus Phytoplasma phoenicium’ was added to the A1 Lists of pests recommended for regulation as quarantine pests in 2017.
Overall assessment of risk: ‘Ca. P. phoenicium’, causal agent of almond witches’ broom, is currently reported only in Iran and Lebanon. Vectors (Asymmetrasca decedens and two Tachycixius species) have been identified and other potential vectors are suspected. A. decedens is polyphagous and present across large parts of the EPPO region. The two Tachycixius vectors are not well known (distribution, hosts).
‘Ca. P. phoenicium’ has had devastating effects on the production of almond, peach and nectarine in Iran and Lebanon with corresponding social and economic impacts. It led to the death and removal of large numbers of trees. Reports also suggest apricot as a host. There are no curative treatments.
The likelihood of entry on pathways was assessed as being:
- high (with a moderate uncertainty) for host plants for planting (except seeds)
- high (with a moderate uncertainty) for natural spread to neighbouring countries without natural obstacles/borders, within 20 years (i.e. Lebanon to Israel or Syria; Iran to Iraq, Turkey or Azerbaijan) [low with a low uncertainty for the rest of the EPPO region]
- low (with a moderate uncertainty) for plants for planting of non-hosts [hosts of the vectors]
- low (with a low uncertainty) for host cut plant parts (cut branches)
The likelihood of entry on all other pathways assessed was rated as very low.
The phytoplasma has a high likelihood of establishing, spreading and causing impacts especially where the known vectors are known to occur. EPPO countries include some of the largest producers of almonds, peaches, nectarines and apricots globally and the pest could also have similar devastating effects in the EPPO region as in Iran and Lebanon.
The EWG determined the need to implement phytosanitary measures on host plants for planting (excluding seeds) to prevent introduction into the PRA area. Based on the experience in Lebanon, it is considered that if the phytoplasma was introduced, early control measures (monitoring, detection and eradication) would significantly reduce the impact of disease. However, early detection is not guaranteed and it is desirable to avoid introduction.
Phytosanitary Measures to reduce the probability of entry: Risk management options were studied for host plants for planting (except seeds)
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