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Diversity of Ralstonia solanacearum in French Guiana Expands Knowledge of the “Emerging Ecotype”

First and third authors: CIRAD, UPR HORTSYS, Campus Agro-Environnemental Caraïbe, F-97285 Le Lamentin, Martinique, France; second, fourth, and fifth authors: CIRAD, UPR Biagresseurs, F-97387 Kourou, French Guiana, France; sixth and tenth authors: CIRAD, UMR 53 Peuplements Végétaux et Bioagresseurs en Milieu Tropical (PVBMT), Pole de Protection des Plantes, 7 chemin de l'IRAT, F-97410 Saint Pierre, Reunion Island, France; seventh author: FREDON, BP 878, F-97333 Cayenne, French Guiana, France; and eighth and ninth authors: DAAF/SALIM, BP 5002, F-97305 Cayenne, French Guiana, France.

Although bacterial wilt remains a major plant disease throughout South America and the Caribbean, the diversity of prevalent Ralstonia solanacearum populations is largely unknown. The genetic and phenotypic diversity of R. solanacearum strains in French Guiana was assessed using diagnostic polymerase chain reactions and sequence-based (egl and mutS) genotyping on a 239-strain collection sampled on the families Solanaceae and Cucurbitaceae, revealing an unexpectedly high diversity. Strains were distributed within phylotypes I (46.9%), IIA (26.8%), and IIB (26.3%), with one new endoglucanase sequence type (egl ST) found within each group. Phylotype IIB strains consisted mostly (97%) of strains with the emerging ecotype (IIB/sequevar 4NPB). Host range of IIB/4NPB strains from French Guiana matched the original emerging reference strain from Martinique. They were virulent on cucumber; virulent and highly aggressive on tomato, including the resistant reference Hawaii 7996; and only controlled by eggplant SM6 and Surya accessions. The emerging ecotype IIB/4NPB is fully established in French Guiana in both cultivated fields and uncultivated forest, rendering the hypothesis of introduction via ornamental or banana cuttings unlikely. Thus, this ecotype may have originated from the Amazonian region and spread throughout the Caribbean region.