Indole‐related Compounds Induce the Resistance to Rice Blast Fungus, Magnaporthe grisea in Barley

When barley leaves pretreated with indole‐3‐acetic acid (IAA), tryptamine and tryptophan solutions at 50 μg/ml, which did not show antifungal activity, were inoculated with Magnaporthe grisea spores 24 h after chemical pretreatments, both blast lesion and infection‐hypha formations were significantly inhibited. Such resistance to M. grisea in barley was induced from 12 h after the pretreatment. In barley leaves pretreated with IAA, tryptamine and tryptophan at 50 μg/ml, phenylalanine ammonia‐lyase (PAL), peroxidase and chitinase activities were already significantly enhanced before M. grisea inoculation, when compared with that in distilled water (DW)‐treated leaves as a control. In chemical‐pretreated leaves, furthermore, H2O2 generation was observed by M. grisea inoculation before lesion formation, but not in DW‐pretreated leaves as a control even by M. grisea inoculation. These results suggested that indole‐related compounds IAA, tryptamine and tryptophan can protect barley from M. grisea as functioning as the plant activator. Studies on indole‐related compounds may contribute to develop new plant activators for disease control.