Genetic diversity among Xanthomonas campestris pv manihotis strains, causal agent of cassava bacterial blight

Cassava bacterial blight was first reported in South America in 1912 and has recently been detected in Africa (1972). Now it has been shown to have a worldwide distribution. To be able to detect and assess evolutionary relationships among pathovar manihotis, a comparison of strains from different geographical origin, was developed using a range of assays. These assays included plant pathogenicity, phenotypic features and most significantly restriction fragment length polymorphism (RFLP) analysis. The probes used were: 16+23SrRNA, genes from E. coli and three restriction fragments from the chromosomal or plasmid DNA. of X.c pv. manihotis (strain CIAT1111). The distinction of four RFLP groups could be possible by using the rRNA probe. Strains from South America were heterogenous and gave different patterns. On the contrary no polymorphism was detected from among African strains. Subgroups were identified based on hybridization profiles with the three other probes. Biochemical and pathogenic variations within the strains studied were reported. Genetic variability of pv. manihotis was more extensive in strains from the area of origin of the host plant and more limited elsewhere. These results agree with the hypothesis of the recent introduction of the pathogen to the other countries and suggests that African strains are not already diversified at the chromosomal level. Our results indicate that probes developed in this study are useful tools for epidemiology studies and in following the genetic evolution of strains. Sumario(spa)