Evolutionary and epidemiological insights from historical and modern genomes of Xanthomonas oryzae pv. oryzicola, the causal agent of bacterial leaf streak of rice.

Xanthomonas oryzae pv. oryzicola (Xoc) causes bacterial leaf streak (BLS) of rice. This disease represents a major constraint for rice production, 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 3 from West-Africa and 7 from Asia also support this hypothesis. East Africa, and 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 i) reconstructed the genome of an historical Xoc strain from herbarium specimen of rice showing symptoms of BLS, sampled in Madagascar in 1931, 50 years before the first description of the disease, and ii) sequenced 9 new modern strains including 5 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.