Exposure of S. nodorum to homocysteine during infection leads to reduced virulence. (A) Detached leaf assays were performed on agar plates in the absence (−) or presence (+) of 300 μM homocysteine. Six leaves for each treatment were inoculated with 5000 spores and ranked according to the severity of symptom development 7 days post inoculation. Based on increasing symptom severity, the infected leaves were assigned to 4 groups of three leaves each. Average numbers of leaves in each of the groups are given in (B). Error bars indicate the standard error of five replicates.