Molecular epidemiology of Xanthomonas axonopodis pv. manihotis to decipher its transmission pathway at a village level in Colombia

Cassava Bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis is an endemic disease in Colombia. CBB can induce important yield losses of cassava when favored by environmental conditions, especially high humidity. But its epidemiology is not well known even though the role of plant material is suspected. X. axonopod is pv. manihotis infects the aerial part but can enter the vascular system. Cassava is propagated by cuttings and planting pieces of stems. In a small - agriculture context of the village of Villa Lopez in the Carribean region of Colombia several sources of cuttings may occur from within or outside the village by purchase or exchange according the farmer status (land owner or tenant). Tenants cannot maintain propagative plant material and have to Following a survey after the rainy season of 2016 in 20 fields of the village, we collected 176 strains of X. axonopodis pv. manihotis. We tried to deduce the epidemiological history of CBB in the village by genotyping the strains and analyzing their genetic relationships. We discriminated 73 haplotypes using the MLVA-14 scheme targeting 14 loci of the pathovar manihotis. Some of these haplotypes were shared by strains originating from different fields either from the village or outside the village. A minimum spanning tree discriminated 1 3 clonal complexes (CCs) composed by strains of different origins. A major CC composed by 14 haplotypes grouped 54 isolates originating from 3 fields of the village and 2 external fields suggesting exchange of contaminated cuttings between the village and producers from other villages. In the case of geographically close fields, natural dispersal might explain the distribution of genetically closely related strains in these fields. Our molecular data are discussed taking into account the epidemiological information given by the producers.