Nematotoxicity of Neotyphodium-infected tall fescue alkaloids and other secondary metabolites on the plant-parasitic nematode Pratylenchus scribneri
Bacetty, Ada Antonia
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Tall fescue (Festuca arundinacea) is a perennial, cool-season turf and forage grass species in the United States that covers over 20 million hectares of pastureland. Neotyphodium coenophialum, an endophytic fungus associated with cool-season grasses, enhances host fitness and imparts pest resistance to the grass. Biologically active alkaloids and other secondary metabolites are produced in this association that not only cause adverse effects on livestock, fescue toxicosis, but may also play a role in the reduction of plant-parasitic nematode populations. Currently there is little information available on the effects of these biologically active compounds on nematodes associated with tall fescue. Therefore, this research examines the interaction of ergot and loline alkaloids, as well as polyphenolic compounds, from endophyte-infected tall fescue on toxicity to the lesion nematode, Pratylenchus scribneri. In vitro bioassays were performed to assess the effects of specifically identified compounds on P. scribneri motility, mortality, and chemoreception. While separate greenhouse studies evaluated the effects of endophyte-infected tall fescue on P. scribneri viability. Root extracts served as nematistatic agents to the nematodes in the chemical submersion assays and affected nematode behavior by acting as repellents in chemoreception studies. During individual tests, ergovaline and [alpha]-ergocryptine were nematicidal at 5[mu]g/ml and 50[mu]g/ml respectively. However, chemotaxis studies revealed [alpha]-ergocryptine as an attractant (1-20[mu]g/ml) and repellent (50-200[mu]g/ml). Ergovaline was an effective repellent (1-5[mu]g/ml) and a nematicidal (10-200[mu]g/ml). Nematistasis was observed in nematodes exposed to ergocornine and ergonovine, but was reversible. Ergonovine was a repellent for P. scriberni, while ergotamine was an attractant. N-formylloline (NFL) was nematicidal at 100-250[mu]g/ml and reversibly nematistatic at 5-50[mu]g/ml. However, NFL also affected nematode behavior similarly to [alpha]-ergocryptine, where it acted as an attractant (1-20[mu]g/ml) and a repellent (50-200[mu]g/ml). The loline mixture of NAL+NFL was also nematicidal (50-200[mu]g/ml) and a repellent (1-20[mu]g/ml). Alkaloid combinations were effectively nematicidal. Greenhouse studies revealed that endophyte-infected tall fescue are essentially non-hosts to P. scribneri populations, with root populations averaging 3.3 to 17.3 nematodes per pot. While, soil populations ranged between 4,866.67 and 8,450 nematodes per pot. This work identified some of the biologically active compounds produced in endophyte-infected tall fescue as nematotoxic and should be further studied to enumerate their modes of action against other plant-parasitic nematodes.