Figure 1.

Airborne resistance induction in lima bean under field conditions. A, Plants treated directly with BTH (direct treatment) or exposed to the air coming from directly treated plants (indirect treatment) were compared with control plants sprayed with sterile distilled water (direct treatment) or exposed to these controls (indirect treatment). To exclude effects of volatile components of BTH, a fifth group of plants was exposed to paper strips on which BTH had been applied. B, Plants were cultivated individually in pots outside for 3 weeks. Then, 10 plants were treated with 0.5 mm BTH solution and 10 further plants were placed immediately beside the treated plants (indirect treatment). Ten further plants received a water spray as controls and were placed close to completely untreated plants. The distance between BTH-treated plants and controls was 4 m. All plants were spray inoculated with P. syringae strain 61 at 5 d after BTH treatment. Bars represent average lesion numbers per leaflet (means ± se). Sample size was n = 10 plants per treatment, and different letters indicate significant differences among treatments (P < 0.001 according to lsd).