GENETIC AND PATHOGENIC VARIATION OF XANTHOMONAS-AXONOPODIS PV. MANIHOTIS IN VENEZUELA

DNA polymorphism and variation in virulence of Xanthomonas axonopodis pv. manihotis (Xam), the causal agent of cassava bacterial blight, wer e studied within a pathogen population from Venezuela. Collections wer e made in several fields at different sites within an edaphoclimatic z one where cassava is a major crop. DNA polymorphism was assessed by RF LP analysis, using an Xam plasmidic DNA sequence (pthB) as a probe to determine the relatedness of 91 Venezuelan isolates. A high degree of polymorphism existed among the isolates, whether collected from the sa me or different fields. Based on a multiple correspondence analysis, t he Xam population was distributed into eight clusters and no correlati on was observed between genetic diversity and geographic origin. One s et of haplotype strains representing the range of variability detected in Venezuela was further characterized by another RFLP analysis using two repetitive genomic probes (pBS6 and pBS8) to establish the useful ness of these probes and their complementarity with the pthB probe. Va riation for virulence was observed in the Xam Venezuelan collection by inoculating a set of cassava cultivars with 28 isolates of the pathog en, each representing a haplotype. Understanding the genetic and patho genic variation in the pathogen population is useful for designing cas sava bacterial blight management strategies.