Candidatus Phlomobacter fragariae is the prevalent agent of marginal chlorosis of strawberry in French production fields and is transmitted by the planthopper Cixius wagneri (China)

Marginal chlorosis has affected strawberry production in France for about 15 years. A phloem-restricted uncultured bacterium, Candidatus Phlomobacter fragariae, is associated with the disease. A large-scale survey for marginal chlorosis in French strawberry production fields and nurseries by polymerase chain reaction amplification of Ca. P. fragariae 16S rDNA revealed that symptoms of marginal chlorosis were not always induced by Ca. P. fragariae and that the stolbur phytoplasma could induce identical symptoms. Ca. P. fragariae was found to be predominant in strawberry production fields, whereas the stolbur phytoplasma was predominantly detected in nurseries. Two transmission periods of the disease, one in spring and the other from late summer to early fall, were evident. Cixius wagneri planthoppers captured on infected strawberry plants were demonstrated to be efficient vectors of Ca. P. fragariae. The involvement in natural disease spread of the whitefly Trialeurodes vaporariorum, previously shown to acquire and multiply Ca. P. fragariae under greenhouse conditions, remains uncertain.