Xanthomonas axonopodis pv.manihotis (Xam) causes bacterial blight, a major disease of cassava, which is a starchy root crop that feeds about 500 million people throughout the world. To better select resistant cassava germplasm, we examined the population structure of Xam in Brazil, Latin America's largest producer of cassava, and a major center of diversity for the crop. The 79 strains collected between 1941 and 1996 from three edaphoclimatic zones were analyzed by restriction fragment length polymorphism (RFLP), using a probe linked to a Xam pathogenicity gene (pthB). Thirty-eight haplotypes were identified, and geographical differentiation for the Xam strains was demonstrated. Strains from subtropical zone (ECZ 6) showed high genetic diversity in most of the sites from which they were collected. They also showed migration from site to site. RFLP and amplified fragment length polymorphism (AFLP) analyses were carried out on 37 Xam strains and compared; the AFLP assays were performed using eight primer combinations. A multiple correspondence analysis, used to assess genetic relatedness among strains and estimate genetic diversity, indicated that the Brazilian Xam population showed high diversity. No correlation was found between AFLP and RFLP data, but the two techniques provided complementary information on the genetic diversity of Xam. Most strains were highly aggressive on a susceptible cultivar. The genetic analysis presented here contributes to a better understanding of the Xam population structure in Brazil and will help select strains of the pathogen for screening cassava germplasm resistant to the disease.Key words: cassava bacterial blight, resistance, genetic diversity, molecular characterization.
Comparative analysis of inter population genetic diversity in Puntius filametosus using restriction fragment length polymorphism (RFLP) analysis
