Disease indices of sugar beets exposed to C. beticola . Plants were infected with conidia of the wild type strains of Ahlburg and Ferrara, with the Ahlburg ctb2 disruption strain 2-1, the Ferrara ctb2 disruption strain 2-1, and with the ectopic transformants of Ahlburg and Ferrara. The disease severity was rated after 21 days. Plants infected with the ΔCTB2 strains of both wild types exhibited no symptoms of infection (disease score 0). The wild type strain Ahlburg and the ectopic transformant Ahlburg showed a disease score of 4. The wild type strain Ferrara and the ectopic transformant Ferrara showed a disease score of 1. Δctb2 mutants did not cause lesions.