Genetic Differences of Geographically Separated Isolates of the Fungus Macrophomina Phaseolina.

Macrophomina phaseolina (Tassi) Goidanich is a soilborne fungus causing charcoal rot in a number of important crops, including soybean, sunflower and sorgum. Its pathogenicity is affected by physiological state of host plants and is increased by drought stress conditions. During the last decade a gradual adaptation to the temperate areas in  US and Europe of the fungus, which is thermophilous fungus of subtropical origin, has been documented. Considering that chemical control is generally not effective and that selection of tolerant genotypes for reducing yield losses have only had limited success, it can be assumed that integrated control strategies of M. phaseolina under climate changing conditions will be required in areas where the pathogen has not been a biotic adversity for the crop. In the present study, 116 strains of M. phaseolina collected from various climatic regions around the world, including both agricultural areas of Europe, North America, and Africa and from different hosts, were subjected to phylogenetic analysis based on transcript spacer (ITS) sequences, and to genotyping analysis of the genomic DNA by random amplified polymorphic DNA. Comparison of internal transcript spacer (ITS) sequences showed a 77% identity. Homology tree constructed from the multiple alignments of the ITS sequence demonstrated that 89% of the screened isolates were characterized by high homology (>91%). Since screened strains were isolates from various climatic areas and from different hosts (soybean, corn, bean, etc.), we concluded that ITS sequences would not clearly discriminate the isolates. In contrast, genotyping analysis of the genomic DNA by random amplified polymorphic DNA revealed high variability among strains isolated from different sites and hosts. Considering the increasing diffusion of this pathogen, this study provides basic information for a understanding of the ecology of M. phaseolina.