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 mug/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 mug/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.