Defoliation and Leaf Age Influence on Ergot Alkaloids in Tall Fescue

A controlled environment experiment was conducted to determinethe influence of defoliation on the regrowth and developmentof two tall fescue (Festuca arundinacea Schreb.) host-endophyte(Neotyphodium coenophialum Morgan-Jones and Gams (Glenn, Bacon,Price and Hanlincomb. nov. ) associations (DN2 and DN11), knownto differ in morphology and alkaloid production capacity. Defoliationtreatments included an uncut control, and clipping to a 5- or10-cm residue height. In a separate experiment, leaf age effectswere determined on an uncut plant canopy. Ergot alkaloid concentrationwas greatest in pseudostem and least in harvested leaf. Non-infectedplants were devoid of alkaloid. Alkaloid production (expressedas a function of dry matter) and yield were greater in uncutthan clipped plants, and were greater in DN11 than DN2 plants.Alkaloid production increased with increasing N concentrationin both associations; however, the rate of production was influencedby concentration of non-structural carbohydrate. Leaf age influencedleaf mass and alkaloid concentration and yield. Oldest leaves(>6 weeks after appearance) of DN2 and DN11 had the lowestconcentrations of ergot alkaloid, while leaves that were 2 to4 weeks old had the greatest alkaloid concentration and yield(alkaloid concentrationxleaf mass). Repeated defoliation reducedthe production of alkaloids, but did so as a function of non-structuralcarbohydrate. Our data suggest that alkaloid production canbe modified by defoliation as well as by host-endophyte association. Neotyphodium coenophialum ; Festuca arundinacea ; N; non-structural carbohydrate