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Abstract

Members of the Ralstonia solanacearum species complex (RSSC) are historically known to cause brown rot of potato and Moko disease of banana in Central America. A novel lineage detected in the island of Martinique in 1999 exhibited a dramatically different host range and pathogenicity profile. This new lineage, referred to as 4NPB, can infect cucurbits Anthurium and Heliconia spp. and is more aggressive on solanaceous crops than previous variants. We sequenced 500 RSSC strains sampled across Martinique and French Guiana during the emergence of this novel lineage. Pangenome and phylogenetic analyses were performed to identify genomic changes linked with the emergence of the new lineage. This analysis reveals the 4NPB population likely emerged from a population of Moko-causing strains found in association with a tomato host on the mainland, followed by dispersal to Martinique. While 4NPB and Moko-causing strains are closely related, variation in the accessory genome includes the exchange of Type 3 secreted effectors and multiple genes with predicted catalytic activity. Recombination hotspots found between 4NPB and Moko strains include various toxin-antitoxin systems, which are potentially involved in intra-species competition and signaling. These changes may underly the altered pathogenicity and host-range profile of 4NPB, contributing to the dramatic expansion of this lineage across Martinique.