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Colletotrichum lindemuthianum is the major pathogen of common bean (Phaseolus vulgaris) in tropical regions. This fungus exhibits diverse physiological races, based on pathogenicity tests conducted on a differential range of bean cultivars. Molecular markers were used to assess the genetic basis of such variability in this fungus which lacks a sexual stage. Random amplification of polymorphic DNA (RAPD), Restriction fragment length polymorphism (RFLP) of the ribosomal genes and RFLP of PCR-amplified internal transcribed spacers of ribosomal DNA were used. A selection of 12 isolates originating from diverse countries or locations was chosen from a collection and analysed for molecular variability and for pathogenicity. Two separate molecular groups were identified. Regarding DNA polymorphism and pathogenicity, a correlation was established within group II since all of the isolates in this group exhibited the same avirulence spectrum, even though they originated from three different continents. Such a correlation could not, however, be established for group I, in which isolates exhibited four different avirulence spectra. Consideration of DNA polymorphism groupings and the geographical origins of isolates suggests that no correlation can be established, as isolates from Latin America are spread throughout both groups. |
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