Reinfection of tall fescue cultivars with non-ergot alkaloid-producing endophytes

For tall fescue (Festuca arundinacea Schreb.) in the southeastern USA, persistence and yield are directly related to infection with a fungal endophyte [Neotyphodium coenophialum (Morgan-Jones & Gams.) Glenn, Bacon, & Hanlin comb. nov.]. However, most endophyte-infected (E+) tall fescue cultivars produce toxic ergot alkaloids resulting in poor weight gain and reproduction in grazing livestock. The objective of this paper was to assess the strategy of reinfecting 'Jesup' and 'Georgia 5' tall fescue with non-ergot alkaloid-producing endophyte strains. Different cultivar-strain combinations were tested against the E+ and endophyte-free (E-) versions of the same cultivars for stand survival and dry matter yield; in separate experiments, they were assessed for toxicity in lambs (Ovis aries). Most cultivar-strain combinations produced no ergot alkaloids but varied in ability to transmit through seed. The best combination, Jesup (AR542), possessed yield and stand survival better (P < 0.05) than the E- checks and equivalent (P < 0.05) to the E + checks. Lambs gained an average of 124 g/d on both cultivars containing AR542, which was equivalent to gains on E- forage but approximately 57% greater than gains on E+ forage. Animals consuming forage from E- or non-ergotproducing strains did not exhibit depressed serum prolactin or elevated body temperatures of animals on E+ forage. The strategy of reinfecting tall fescue cultivars with naturally occurring, non-ergotproducing endophytes appears promising for removing toxicity symptoms and retaining agronomic performance, but intense screening is needed to identify the best cultivar-strain combinations.