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Toxicity of Endophyte-Infected Tall Fescue Alkaloids and Grass Metabolites on Pratylenchus scribneri

First, second, third, and ninth authors: United States Department of Agriculture--Agricultural Research Service (USDA-ARS), Toxicology and Mycotoxin Research Unit, Richard Russell Research Center, Athens, GA; first, fourth, and sixth authors: Department of Plant Pathology, and fifth author: Department of Crop and Soil Science, University of Georgia, Athens; seventh author: USDA-ARS, Crop Protection and Management, Tifton, GA; and eighth author: Department of Plant Pathology, University of Kentucky, Lexington.

Neotyphodium coenophialum, an endophytic fungus associated with tall fescue grass, enhances host fitness and imparts pest resistance. This symbiotum is implicated in the reduction of stresses, including plant-parasitic nematodes. To substantiate this implication, toxicological effects of root extracts, polyphenolic fraction, ergot, and loline alkaloids from endophyte-infected tall fescue were investigated using Pratylenchus scribneri, a nematode pest of tall fescue. In vitro bioassays and greenhouse studies were used as tests for effects of root fractions and compounds on motility and mortality of this lesion nematode. Greenhouse studies revealed that endophyte-infected tall fescue grasses are essentially nonhosts to P. scribneri, with root populations averaging 3 to 17 nematodes/pot, compared with 4,866 and 8,450 nematodes/pot for noninfected grasses. The in vitro assay indicated that root extracts from infected tall fescues were nematistatic. Polyphenols identified in extracts included chlorogenic acid, 3,5-dicaffeoylquinic acids, caffeic acid, and two unidentified compounds, but these were not correlated with endophyte status, qualitatively or quantitatively. Tests of several ergot alkaloids revealed that ergovaline and α-ergocryptine were nematicidal at 5 and 50 μg/ml, respectively, while ergocornine and ergonovine were nematistatic at most concentrations. Loline (N-formylloline), the pyrrolizidine alkaloid tested, was nematicidal (50 to 200 μg/ml). The ecological benefits of the metabolites tested here should assist in defining their role in deterring this nematode species while offering some probable mechanisms of action against plant-parasitic nematodes in general.

Additional keywords:Festuca arundinacea, fungal endophyte, Lolium arundinaceum, pyrrolizidine alkaloids.