Abstract
Xanthomonas oryzae pv. oryzicola (Xoc) causes bacterial leaf streak (BLS) of rice. This disease represents a major constraint for rice production, which is a crop feeding more than half of the world's population. Xoc was first described in 1918 in the Philippines and is prevalent in southeast Asia. Today, BLS is also omnipresent in both East- and West-Africa, where the disease was first reported in the early 1980s. The appearance of Xoc in Africa decades after its first report in Asia suggests that the disease could have been introduced from Asia to Africa. Strict conservation of five transcription activator-like (TAL) effectors in whole-genome sequences of 10 strains of Xoc including three from West-Africa and seven from Asia also support this hypothesis. East-Africa, especially Madagascar, where the disease was first described in 1985 is located at the interface between Asia and Africa, hence representing an interesting region to explore the link between strains from Asia and West-Africa. In this study, we did the following: (i) reconstructed the genome of a historical Xoc strain from a herbarium specimen of rice showing symptoms of BLS that was sampled in Madagascar in 1931, 50 years before the first description of the disease, and (ii) sequenced nine new modern strains, including five from Madagascar and East-Africa. The analysis of those new genomes along with previously published ones shed light within the evolutionary and epidemiological history of Xoc