A new phytoplasma disease of almond (Prunus amygdalus) in Lebanon: Addition to the EPPO Alert List
The EPPO Secretariat recently received the note below, written by E. Choueiri, F. Jreijiri, S. Issa, (Agricultural Research Institute of Lebanon, Tal Amara, Rayak, Lebanon) and E. Verdin, J. Bové, M. Garnier (INRA, Villenave d’Ornon, France), on the presence of a new phytoplasma disease of almond in Lebanon. Considering the fact that this new disease has the potential to kill mature trees and therefore represents a threat to the production of almond in Mediterranean countries, the EPPO Secretariat decided to add it on the EPPO Alert List.
‘During a survey conducted in October 1999 to establish the sanitary status of stone fruits in Lebanon, almond trees with symptoms of leaf yellowing, shoot proliferation, and dieback were observed in the Bekaa region. Such symptoms suggesting a phytoplasma infection, PCR analysis with universal primers for amplification of phytoplasma ribosomal RNA genes was carried out on DNA extracted from nine symptomatic trees and one symptomless tree in four different orchards, as well as from healthy almond trees collected in France. Amplification of the expected 1.8 kbp rDNA fragment from all symptomatic samples but not from the healthy or symptomless samples established the phytoplasma etiology of the disease. RFLP of the amplified DNA, showed that restriction profiles were different from those published for other phytoplasmas and in particular those infecting almond trees in Western Europe. Sequence analysis of the amplified DNA revealed that the phytoplasma belongs to the pigeon pea witches’ broom cluster (PPWB). This indicates that a phytoplasma infection is occurring in almond trees in Lebanon and for the first time, a phytoplasma of the PPWB group is shown to infect a Prunus species. This phytoplasma is killing almond trees within 5 years and represent a threat to European and Mediterranean countries.’
A new phytoplasma disease of almond (Prunus amygdalus)
Why: This new phytoplasma disease of almonds came to our attention because scientists (Choueiri et al., 2001) who have observed it in Lebanon alerted the EPPO Secretariat on their finding.
Where: Lebanon, in the Bekaa region. However, it is not known whether the disease is present in other parts of Lebanon or even in other countries.
On which plants: Almond (Prunus amygdalus).
Possible identity: A new phytoplasma belonging to the pigeon pea witches’ broom cluster.
Damage: Affected trees show leaf yellowing, shoot proliferation and dieback. The disease can kill almond trees within 5 years.
Transmission: Further studies are needed, in particular on possible insect vectors.
Pathway: Almond plants for planting or multiplication material from Lebanon.
Possible risks: For the moment only very few data are available on the extent of the disease, on its biology and epidemiology. However, as tree mortality is reported, it was felt that this disease could represent a threat for almond-producing countries.
EPPO RS 2001/094
Panel review date - Entry date 2001-05
E. Choueiri, F. Jreijiri, S. Issa, E. Verdin, J. Bové, M. & Garnier (2001). First report of a phytoplasma disease of Almond (Prunus amygdalus) in Lebanon. Plant disease (2001) in press
Personal communications with Dr Choueiri (Agricultural Research Institute of Lebanon) and Dr Garnier (INRA, Villenave d’Ornon, France), 2001-05.