Genetic diversity of Xanthomonas oryzae pv. oryzicola from West Africa

Bacterial Leaf Streak (BLS) caused by Xanthomonas oryzae pv. oryzicola (Xoc) was first reported in Africa in the 1980s. Following the recent expansion of rice cultivation in West Africa, a substantial reemergence of BLS was observed in Burkina Faso and Mali. Xoc strains were isolated from cultivated and wild rice varieties showing BLS symptoms. Samples were collected at various sites in three different regions of Burkina Faso and Mali, respectively. A collection of 58 Xoc strains was evaluated for virulence on rice varieties. African Xoc strains showed high variation in lesion length on susceptible cultivars. A set of strains was further characterized using a MultiLocus Sequence Analysis using seven housekeeping genes. Dendrograms generated for the data sets obtained from MLSA clearly separated different groups among African Xoc. RFLP analysis was performed using the TALE avrXa7 as a probe, resulting in the identification of six haplotypes. PCR-based analyses of two conserved TTSS (avrRxo1 and xopW) also differentiated the strains into distinct groups. avrRxo1 was detected in only 30% of African Xoc strains. Functionality of avrRxo1 was confirmed by leaf infiltration on rice Kitaake Rxo1 lines. Sequence analysis of xopW revealed three distinct groups among Asian and African Xoc strains. Together, our results demonstrate that African Xoc strains, while differentiable from the Asian strains, are highly diverse and rapidly evolving.