Pathogenic Variation of Macrophomina phaseolina Isolates and Resistance of Soybean Genotypes to the Fungus In vitro and Greenhouse Conditions

Charcoal rot caused by Macrophomina phaseolina is an important disease of soybean in Iran. Effective and reliable techniques are needed to select aggressive isolate of the pathogen and evaluate resistance of soybean genotypes to the pathogen. In the present study, 32 isolates of the pathogen from different oilseed crops were examined in vitro, and So.3 was selected as the most aggressive isolate for resistance evaluation. Resistance of seven soybean genotypes was then evaluated in vitro and greenhouse conditions using toothpick and stem cut inoculation methods. Genotypes differed significantly for pathogenicity index in both inoculation methods. Genotypes Hatcheston, Sari, Hamilton and Katol had lower pathogenicity index compared to the other genotypes. Hacheston with the lowest infection at seedling stage, and L.17 and Williams with the highest infection, were evaluated as the most resistant and susceptible genotypes, respectively.