With the increase in the world population, there is a need for an increase in the agricultural production of food. In this scenario, weeds can sometimes be responsible for as much as 60% of crop losses, making agriculture highly dependent upon chemicals for weed management. Unfortunately, with indiscriminate, repetitive and continuous use of herbicides, the number of resistant weeds has increased. Currently, there are several types of herbicides available, but they all have mechanisms of action that were introduced 30 or more years ago, which helps explain the evolved resistance, leading farmers to sometimes increase application rates, putting human health and the environment at risk. Recent research shows that secondary metabolites produced by fungi are promising for the development of natural herbicides, as they exhibit activity at low concentrations, in addition to being considered by some safer than synthetic alternatives. We focused on evaluating the herbicidal activity of a phytopathogenic fungus isolated from leaf lesions of Handroanthus serratifolius (Bignoniaceae) seedlings showing signs of infection. The fungus was collected in Rio Doce State Park, a native fragment of the Atlantic Forest in the state of Minas Gerais, Brazil, and was isolated and grown in potato dextrose agar culture medium and identified as Xylaria sp. The dichloromethane extract of the culture displayed high phytotoxic activities against lettuce (Lactuca sativa) and bentgrass (Agrostis stolonifera), effectively inhibiting the germination of all the seeds at concentrations of 1 mg mL^-1. Following different chromatographic steps, grammicin (1) and xylaric acid methyl ester (2) were isolated and identified. Grammicin was responsible for the phytotoxic activity, inhibiting growth of Lemna paucicostata (duckweed) by 50% at 87.7 μM. This is the first report of the phytotoxic activity of grammicin. Mode of action studies are in progress. These findings highlight the potential sourcing of phytopathogenic fungi found within the Brazilian Atlantic Rain Forest's plant ecosystem to produce secondary metabolites with herbicidal properties. This discovery positions these fungi as valuable sources for investigating natural herbicides with potentially novel mechanisms of action.

Stephen Duke

USDA/ARS

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