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“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)

First, second, third, fourth, fifth, and seventh authors: Laboratoire de Biologie Cellulaire et Moléculaire, UMR Génomique, Développement et Pouvoir Pathogène, Institut de Biologie Végétale Moléculaire, INRA et Université Victor Ségalen Bordeaux 2, BP 81-33883, Villenave d'Ornon, Cedex-France; and sixth author: Unité Mixte de Recherche en Santé Végétale, Institut National de la Recherche Agronomique, 33883, Villenave d'Ornon cedex, France

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.

Additional keyword: proteobacteria.