Contrasting toxic-endophyte contamination between endophyte-free and nontoxic-endophyte tall fescue pastures

The fungal endophyte Neotyphodium coenophialum Morgan-Jones and Gams is abundant in tall fescue (Festuca arundinacea Schreb.) and one strategy to alleviate detrimental effects on livestock is to plant endophyte-free cultivars; however, these pastures frequently become recontaminated by toxic-endophyte tall fescue. An alternative strategy is to use pastures of tall fescue infected with endophyte that does not produce toxic alkaloids. Our objective was to test the hypothesis that nontoxic-endophyte infected tall fescue swards (Nontoxic-E) were more resistant to reinfestation by volunteer tall fescue and its associated toxic endophyte, than endophyte-free tall fescue swards (E-). Plots of E- and Nontoxic-E tall fescue (cultivar Jesup) with six levels of contamination by endophyte-infected K31 (0, 10, 20, 30, 40, 50% of viable seed weight) were established from seed at three sites in Ohio during April 2001. Observed endophyte levels for E- at the Jackson site were 77, 118, and 143% greater than expected in autumn 2001, spring 2002, and autumn 2002, respectively. Observed endophyte levels for E- at the Belle Valley site were 32, 70, and 39% greater than expected in autumn 2001, spring 2002, and autumn 2002, respectively. Observed endophyte levels for E- at the South Charleston site averaged 8% less than expected. Observed endophyte levels in Nontoxic-E at all sites were consistent with the endophyte levels in the seed that was planted, and plants had a negligible concentration of ergopeptine alkaloids. It was concluded that, where mechanisms for contamination exist, E- tall fescue stands can be readily contaminated by volunteer tall fescue and its toxic endophyte; but, Nontoxic-E tall fescue is less susceptible to contamination by volunteer tall fescue.