Bacterial Leaf Streak (BLS) caused by Xanthomonas oryzae pv. oryzicola (Xoc) was first reported in Africa in the 1980s. Recently, a substantial reemergence of this disease was observed in West Africa. Samples were collected at various sites in five and three different rice growing regions of Burkina Faso and Mali, respectively. Sixty seven Xoc strains were isolated from cultivated, wild rice varieties and from weeds showing BLS symptoms. Xoc strains were evaluated for virulence on rice and showed high variation in lesion length on a susceptible cultivar. Xoc strains were further characterized by Multi Locus Sequence Analysis (MLSA) using six housekeeping genes. Inferred dendrograms clearly indicated different groups among Xoc strains. RFLP analysis using the Transcriptional Activator Like Effector avrXa7 as probe, resulted in the identification of 18 haplotypes. PCR-based analyses of two conserved type III effector (T3E) genes (xopAJ and xopW) differentiated the strains into distinct groups with xopAJ not detected in most African Xoc strains. XopAJ functionality was confirmed by leaf infiltration on rice Kitaake Rxo1 lines. Sequence analysis of xopW revealed four groups amongst Xoc strains. Distribution of 43 T3E genes shows variation in a subset of Xoc strains. Together, our results show that African Xoc strains are diverse and rapidly evolving with a group endemic to Africa and another one that may have evolved from Asian strain.
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