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MLVA-based diversity analysis of Xanthomonas axonopodis pv. manihotis (Xam) populations in Mali.

Moussa Kante: Université de Segou , IRD , LBMA

<div>Cassava Bacterial Blight (CBB) caused by the bacterium <em>Xanthomonas axonopodis </em>pv.<em>manihotis </em>(<em>Xam</em>) occurs on several continents including West Africa where it has recently been reported in Burkina Faso and Ivory Coast, sometimes imposing severe yield losses.</p> <p>The genetic diversity of CBB in Mali, a country bordering both Burkina Faso and Ivory Coast, was investigated in 2015 in two cassava production regions (Bamako and Ségou). Forty strains were isolated from cassava leaves showing angular leaf spots symptoms typical of CBB. Colonies were identified as <em>Xam </em>after specific PCR diagnostic tests and pathogenicity assays. The Koch postulate was further validated.</p> <p>Subsequently, a multilocus variable number of tandem-repeat (VNTR) analysis (MLVA) scheme based on 14 microsatellites discriminated 18 haplotypes out of the 40 isolates. The two populations of Ségou and Bamako were genetically differentiated (RST = 0.262, P <0.001). A greater diversity was observed in the population of the Bamako region compared to that of Ségou with an allelic richness of 2.96 and 2.07, respectively. A unique haplotype was shared by strains from Bamako and Ségou but strains from both regions are associated in different clonal complexes supporting epidemiological link between those two regions.</p> <p>New surveys carried out in 2016 in five production areas have made it possible to isolate 29 populations (corresponding to over 300 <em>Xam </em>strains), whose Analysis of the genetic structure is in progress. The data collected will help to rationalize the use of casava variety grown in Mali.</div>