AbstractThe damages observed in Tunisian citrus orchards have prompted studies on thePseudomonasspp.responsible for blast and black pit. Prospective orchards between 2015 and 2017 showed that the diseases rapidly spread geographically and to new cultivars. A screening ofPseudomonasspp. isolated from symptomatic trees revealed their wide diversity according to phylogenetic analysis of their housekeepingrpoDandctsgenes. The majority of strains were affiliated toPseudomonas syringaepv.syringae(Phylogroup PG02b), previously described in Tunisia. However, they exhibited various BOX-PCR fingerprints and were not clonal. This work demonstrated, for the first time in Tunisia, the involvement ofPseudomonas cerasi(PG02a) andPseudomonas congelans(PG02c). The latter did not show significant pathogenicity on citrus, but was pathogenic on cantaloupe and active for ice nucleation that could play a role in the disease. A comparative phylogenetic study of citrus pathogens from Iran, Montenegro and Tunisia revealed thatP. syringae(PG02b) strains are closely related but again not clonal. InterestinglyP. cerasi(PG02a) was isolated in two countries and seems to outspread. However, its role in the diseases is not fully understood and it should be monitored in future studies. The diversity of pathogenicPseudomonasspp. and the extension of the diseases highlight that they have become complex and synergistic. It opens questions about which factors favor diseases and how to fight against them efficiently and with sustainable means.