Phylogenetical characterization and PCR detection of a new phytoplasma in almond <em>(Prunus amygdalus</em>) and peach (<em>Prunus persica</em>) in the mediterranean area

19. International Symposium on Virus and Virus-Like Diseases of Temperate Fruit Crops, Valence, Spain, 2003/07/21-25

International audience

anglais. Recently, a new and devastating disease of almond trees (Prunus amygdalus) characterized by the development of witches-brooms leading to tree death within a few years emerged in Lebanon. The presence of a phytoplasma was demonstrated in diseased trees by electron microscopy and could be graft-transmitted to almond and other Prunus species (P. persicae and P. mariana) seedlings. DNA amplification with universal phytoplasma 16S rDNA primers followed by sequence analysis showed that the phytoplasma belongs to the 16SrIX-A or Pigeon Pea Witches-broom (PPWB) group. Phylogenetical analysis confirmed that the almond phytoplasma was a member of the PPWB cluster of the class Mollicutes. These analyses also showed the almond phytoplasma from Lebanon to be identical to a phytoplasma inducing almond brooming in Iran, but differed from two PPWB group-phytoplasmas naturally infecting herbaceous plants in Lebanon (wild lettuce: Lactuca serriola, and periwinkle: Catharanthus roseus). The phytoplasma infecting almond trees in Lebanon and Iran was given the species name "Candidatus Phytoplasma phocnicium". Oligonucleotides have been designed within the 16S-23S operon for specific detection of "Ca. P. phoenicium". These primers allow PCR amplification for many affected almond trees in Lebanon but also in one peach tree. This PCR test is now used to identify reservoir plants and leafhopper or psyllid carriers of the phytoplasma.