Infection of Tall Fescue Cultivars with Non-toxic Endophytes

For tall fescue in the southeastern USA, long term persistence, competitiveness, yield, and summer survival are directly related to the presence of a fungal endophyte (Neotyphodium coenophialum; formerly called Acremonium coenophialum) living in the fescue plant. However, cattle grazing forage from the predominant USA tall fescue cultivars infected with their naturally occurring endophyte strains (E+) suffer from a condition called "Fescue Toxicosis". Occurrence of fescue toxicosis is associated with the presence of this endophytic fungus. Endophyte Effects on Summer Survival Summer drought results in the greatest loss of tall fescue stands in the southeast. Table 1 dramatically shows the value of infection with the N. coenophialum endophyte for survival in a very hot, dry summer in Georgia (Bouton et al. 1993a). Literally, the endophyte-free (E-) versions of all cultivars in this particular experiment died completely while the E+ versions maintained good stands. Another stress factor for tall fescue pastures is encroachment by bermudagrass. This aggressive, warm season grass has been observed to reduce the stands of both E+ and E- tall fescue especially when combined with grazing in hot, dry summers. To better assess the effect of both bermudagrass competition and grazing, E+ and E- tall fescue cultivars were tested under grazing or hay clipping management after their establishment in tilled soil or bermudagrass sod seeded conditions (Table 2). The positive effect of endophyte infection on plant survival was seen by the better survival of E+ ‘Georgia 5' compared to E- ‘AU Triumph’ in all testing conditions. Grazing, when combined with bermudagrass competition, created the greatest stress for tall fescue survival. For future studies to rapidly assess stand persistence of either E+ or Etall fescue cultivars, plots can be established in bermudagrass sods and grazed. Besides defining a worse-case but real-world scenario in the southeast region, this type of screening procedure allows cultivars to be assessed more quickly and efficiently.