In vitro susceptibility of Erwinia amylovora (Burrill) Winslow et al. to geraniol and citronellol

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Abstract
The in vitro antimicrobial activity of geraniol and citronellol towards seven strains of Erwinia amylovora, the causal agent of ‘fire blight’of Rosaceous plants, was assessed in tube cultures. All of the strains tested at 1 × 105 cfu/ml were inhibited for 24 h by geraniol in the range 600–1500 mg/1, whereas its minimum bactericidal concentration was 800–1700 mg/1. Citronellol was less effective, being bactericidal for only two of seven strains. RIF‐NY, isolated from apple orchards, was relatively resistant to geraniol; 1700 mg/1 of the chemical only reduced the growth of an inoculum of 1 × 107 cfu/ml. In general, such terpenoids commenced exerting a bactericidal effect 6 h after addition to the suspensions, even if geraniol added at 1700 mg/1 to 1 × 103 cfu/ml of five strains, commenced its bactericidal activity earlier than 6 h.