Ergot alkaloids are not essential for endophytic fungus-associated population suppression of the lesion nematode, Pratylenchus scribneri, on perennial ryegrass

Several endophytic fungi of the genus Neotyphodium form symbiotic associations with Lolium spp. grasses and are renowned for production of bioactive alkaloids such as ergot alkaloids. Some of these endophytes make their grass partners less suitable as hosts for endoparasitic nematodes, including Pratylenchus spp. The potential for ergot alkaloids to affect nematode motility was investigated in vitro. Ergovaline, the ergot alkaloid pathway end product of several Neotyphodium spp., was the only ergot alkaloid tested that inhibited motility of Pratylenchus scribneri. The association of ergot alkaloids with nematode population suppression was examined in glasshouse experiments with strains of the perennial ryegrass endophyte Neotyphodium sp. isolate Lp1 (syn. Neotyphodium lolii x Epichloë typhina) that have been genetically modified to lack ergot alkaloids or to have an altered ergot alkaloid profile. Populations of P. scribneri were significantly smaller in pots of perennial ryegrass containing the wild-type, ergot alkaloid-producing endophyte than in pots of endophyte-free perennial ryegrass. Elimination of certain complex ergot alkaloids (ergovaline and lysergic acid amides) in one gene knockout strain, or complete elimination of ergot alkaloids in another, did not affect the ability of the endophyte to suppress populations of nematode. Presence and concentrations of ergot alkaloids in pseudostems were as expected based on presence and genotype of endophyte in each plant, but frequently were undetectable or in low concentration in roots. The data indicate that ergot alkaloids do not contribute significantly to the endophyte-associated suppression of Pratylenchus spp.