A phytotoxic and antifungal metabolite (Pyrichalasin H) from a fungus infecting Brachiaria eruciformis (Signal Grass)

Authors: Meepagala, Kumudini; CLAUSEN, BRANDON - Former ARS Employee; Johnson, Robert; Wedge, David; Duke, Stephen

Submitted to: Journal of Agricultural Chemistry and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2019
Publication Date: 8/8/2019
Citation: Meepagala, K.M., Clausen, B., Johnson, R.D., Wedge, D.E., Duke, S.O. 2019. A phytotoxic and antifungal metabolite (Pyrichalasin H) from a fungus infecting Brachiaria eruciformis (Signal Grass). Journal of Agricultural Chemistry and Environment. 8(3):115-128. https://doi.org/10.4236/jacen.2019.83010.
DOI: https://doi.org/10.4236/jacen.2019.83010

Interpretive Summary: Signal grass also locally known as “sweet signal grass”, is a common weed in lawns and turfs in the state of Mississippi. During late spring and early summer months, the leaves of signalgrass are infected with a fungus causing dark reddish brown spots. The infected leaves ultimately turn brown and wither. We believe that this fungus produces compounds that are toxic to plants and have the potential as natural herbicides. As part of our search for natural product-based agrochemicals, we studied this fungus in order to investigate compounds that are toxic to plants. The causative fungus was isolated from an infected leaf of signal grass and grown in a liquid culture medium. This fungus was identified via molecular techniques as Pyricularia grisea. The compound toxic to plants was isolated from liquid culture medium and identified as pyrichalasin H. Pyrichalasin H was toxic to the plant pathogen Colletotrichum fragariae and toxic to lettuce and agrostis. This is the first report of antifungal activity of pyrichalasin H.

Technical Abstract: Brachiaria eruciformis (sm.) Griseb, locally known as “sweet signalgrass”, is a common weed in lawns and turfs in the state of Mississippi, USA. During late spring and early summer months, the 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 natural product-based agrochemicals, we studied this plant pathogen in order to investigate phytotoxic metabolites produced by the fungus. The causative fungus was isolated from an infected leaf of B. eruciformis, and cultured in potato dextrose agar plates. This fungus was identified via molecular techniques as Pyricularia grisea. The phytotoxic compound was isolated from liquid culture medium and identified as pyrichalasin H by spectroscopic techniques. Pyrichalasin H was toxic to the 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.