Quantitation of toxin levels in various isolates. Toxin production was not detectable for the Ahlburg cbt2 disruption strain 2-1 and the Ferrara cbt2 disruption strain 2-1. Similar results were obtained for mutants AΔctb2-2 and FΔctb2-2 (data not shown). The more virulent wild type Ahlburg produced 750 μM cercosporin compared to 320 μM cercosporin detected for Ferrara, the less virulent isolate. The ectopic Ferrara mutant produced toxin levels comparable to the Ferrara wild type. Extractions were repeated three times for each isolate. Standard deviations are marked in columns by black lines.