Lavender decline in France is associated with chronic infection by lavender-specific strain of “Candidatus Phytoplasma solani”
Résumé
Lavender decline compromises the French lavender production, and preliminary data have suggested the involvement of “Candidatus Phytoplasma solani” in the etiology of the disease. In order to evaluate “Ca. P. solani” epidemiological role, a three year survey was conducted in Southeastern France. “Ca. P. solani” was detected in 19 to 56 % of the declining plants, depending on 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 fluctuated over months supporting the chronicity of infection. Three ‘Ca. P. solani" secY genotypes S17, S16 and S14 were the most prevalent in lavender fields and were also detected in nurseries, whereas strains detected in surrounding bindweed and wild carrots were mostly of the S1 and S4 genotypes. This suggests lavender is the main pathogen reservoir of the epidemic. Adults and nymphs of the planthopper vector Hyalesthes obsoletus were commonly captured in lavender fields and were shown to mainly harbor the prevalent phytoplasma genotypes detected in lavenders. The “Ca. P. solani” genotype S17 was 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 rRNA deep-sequencing ruled out the involvement of other phloem-limited bacterial pathogens.
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