A Phytotoxic and Antifungal Metabolite (Pyrichalasin H) from a Fungus Infecting <i>Brachiaria eruciformis</i> (Signal Grass)

Abstract

Brachiaria eruciformis (sm.) Griseb, locally known as “signal grass”, is a common weed in lawns and turfs in Mississippi, USA. During late spring and early summer months, leaves of B. eruciformis are infected with a fungus causing necrosis. The infected leaves ultimately turn brown and wither. As part of our search for potential new natural product-based agrochemicals, we studied this plant pathogen in order to investigate phytotoxic and fungitoxic metabolites produced by the fungus. The causative fungus was isolated from an infected leaf of B. eruciformis, cultured in potato dextrose agar plates and identified via molecular techniques as Pyricularia grisea. A phytotoxic compound was isolated from Czapek-Dox broth liquid culture medium and identified as pyrichalasin H by spectroscopic techniques. Pyrichalasin H was toxic to the fungal plant pathogen Colletotrichum fragariae in a TLC bioautography assay and phytotoxic to two monocot and one dicot plants. This is the first report of antifungal activity of pyrichalasin H against phytopathogens. Pyrichalasin H isolated from Pyricularia grisea, a pathogen infecting B. eruciformis (signal grass) was shown to be phytotoxic and fungicidal to Colletotrichum fragariae.