Submitted to: International Neotyphodium Grass Interactions
Publication Type: Proceedings
Publication Acceptance Date: 2/28/2007
Publication Date: 3/25/2007
Citation: Bacetty, A.A., Snook, M.E., Glenn, A.E., Bacon, C.W., Nagabhyru, P., Schardl, C.L. 2007. Nematotoxic effects of endophyte-infected tall fescue toxins and extracts to an in vitro bioassay using the nematode Pratylenchus scribneri. Proceedings of New Zealand Grassland Association: Endophyte Symposium. 6th International Symposium on Fungal Endophytes of Grasses. p. 357-361. Interpretive Summary: A fungus, Neotyphodium coenophialum, lives within the tissues of tall fescue as an endophyte. This grass is valuable forage for the south and southeast. However, this grass is toxic to cattle, which is due to specific cattle toxin produced by this endophyte. There are strains of this endophytic fungus that provides beneficial protection to the grass and one of these is resistance to the soil pest nematode that kill this and other plants. It is desired to determine the specific toxins that kill the nematodes. We modified a sterile in vitro system that is rapid and can determine the interactive nature of known endophyte toxins and compounds produced by the grass. This assay used sterile the lesion nematode Pratylenchus scribneri as the target organism to determine the interactive nature of the cattle toxins, other suspect compounds and grass extracts. This assay is described along with methods for testing toxicity to this nematode. The results indicate that only two of three ergot cattle toxins were toxic to this nematode, and that there were other toxins involved. This in vitro assay offers a rapid and routine screen for acute testing of chemical components of the tall fescue for toxicity to this nematode species.
Technical Abstract: Biotypes of the Neotyphodium coenophialum-tall fescue grass symbiota are provided with enhanced protection from grazing vertebrate herbivores due to the production of toxic secondary metabolites. However, considerable controversy exists concerning this symbiotum and its toxicity to nematode species. A sterile in vitro system was developed to determine the interactive nature of known toxins specific to this mutualistic association and compounds within grass extracts known to be nematotoxic. The in vitro assay used Pratylenchus scribneri, the lesion nematode, as the target organism to determine the interactive nature of ergot alkaloids, the pyrrolizidine alkaloid (the lolines), total phenolic fractions, and specific phenolic compounds. The in vitro assay is described along with methods for testing toxicity. The results indicate that only two of three ergot alkaloids were toxic to P. scribneri, and there were possible potentiating or synergistic effects with other alkaloids and water soluble polyphenolics. HPLC analysis and UV mass spectrometry of root extracts revealed the presence of two major polyphenolics, chlorogenic and di-caffeoylquinic acids, both of which are natural constituents of this and other plants and have known toxicity to several species of nematodes. Further, it was determined that there were quantitative differences between the total phenolic and specific phenolic contents in roots of endophyte infected and noninfected tall fescue, cultivar Jesup. This in vitro assay offers a rapid and routine screen for acute testing chemical components of the tall fescue-endophyte symbiotum for toxicity to this nematode species.