Abstract: The pathogenic diversity among and within 12 mycelial compatibility groups (MCGs)previously identified from a population of 459 Sclerotium rolfsii isolates infecting autumn-sownsugar beet crops in Mediterranean-type climate regions of Chile, Italy, Portugal, and Spain weredetermined to 11 economically important host crops. Across the tested plant species, MCG ii andiv were highly virulent, MCGs i, iii, ix and x moderately virulent and MCGs iv, v, vii, viii, xi andxii were low virulent. Similarly, across MCGs, chickpea and sunflower were highly susceptible,pepper, watermelon, cotton and tomato susceptible, broccoli, sugar beet, and melon, moderatelysusceptible, and wheat and corn were resistant. There was no MCG-host species significantinteraction. Establishing the variability in virulence among S. rolfsii isolates is of importance formanagement of Sclerotium root rot diseases in crops that can potentially be affected.