Genes for antigenic membrane protein STAMP of 'Candidatus Phytoplasma solani' isolates detected in French lavender fields. Genetic diversity of 'Candidatus Phytoplasma solani' in French lavender fields

Lavender decline drastically compromises the French lavender production and first evidences have suggested the involvement of ‘Candidatus Phytoplasma solani’ in the etiology of the disease. In order to evaluate its epidemiological role, a three years survey was conducted in Southeastern France. ‘Ca. P. solani’ was detected in 19 to 56 % of the declining plants according to seasons and cultivars and its prevalence was correlated with symptom severity. Autumn was more favorable than spring for phytoplasma detection and ‘Ca. P. solani’ incidence was higher in Lavandula angustifolia than in L. intermedia hybrids. Detection of the phytoplasma strongly fluctuated overtime supporting the chronicity of infection. Three ‘Ca. P. solani’ secY genotypes S17, S16 and S14 highly prevailed and were also detected in nurseries, whereas strains detected in surrounding bindweed and carrots were mostly of the S1 and S4 genotypes. This incriminates the lavender themselves as the main reservoir of the epidemic. Adults and nymphs of the planthopper vector Hyalesthes obsoletus, could be commonly captured in lavender fields and were shown to mainly harbor the prevalent phytoplasma genotypes detected in Lavenders. The ‘Ca. P. solani’ genotype S17 could be transmitted to Catharanthus roseus periwinkle by naturally infected H. obsoletus. Finally, the inventory of the bacterial community of declining lavenders that tested negative for ‘Ca. P. solani’ by 16S deep-sequencing, ruled out the involvement of other phloem-limited bacteria although ‘Ca. P. trifolii’ could be occasionally detected in declining lavenders.