The adverse effect of the tall fescue (Festuca arundinacea Schreb.) fungal endophyte (Acremonium coenopltialum Morgan-Jones and Gams) on animal performance is well recognized but the mutualistic effect of this fungus-grass association under environmental stress is not well understood. The objective of this study was to evaluate endophyte-free (EF) and endophyte-infected (EI) tall fescue plants from one clone for morphological and physiological responses to flooding, N rates (11, 73, and 220 mg N pot-•), and -0.03, -0.05 and -0.50 MPa drought stress in the greenhouse. Plants were grown in a synthetic mixture of the following by volume: Cecil sandy clay loam (clayey, kaolinitic, thermic Typic Hapludult) (33%), sand (16%), peat moss (17%), perlite (17%), and vermiculite (17%). Leaf blades of EI, as compared to EF plants were thicker and narrower regardless of flooding, N rate, or drought stress. Plant ultrastructure was not appreciably altered by the endophyte. Herbage growth was 50% greater on EI than EF plants, especially at higher N levels. Tillering increased on EI plants but only at the highest N rate. The EI plants were more productive than EF plants at mild soil moisture stress ( -0.05 MPa). At more severe stress ( -0.5 MPa) 75% of EF plants died and all EI plants survived. Leaf rolling under drought stress was much more common in EI than EF plants. Regrowth after harvest with abundant watering of previously drought-stressed plants was much greater on EI than EF plants. There was little or no difference in digestibility of forage from EI and EF plants. The results indicate that there are positive benefits derived from association of an endophyte with tall fescue resulting in growth stimulation, improved survival, and drought tolerance to the host plant that could be important in plant competition.

No abstract

Tall fescue (Festuca arundinacea Schreb.), a well adapted pasture grass in the eastern USA, has a reputation for poor animal performance. Discovery of an association between the fungal endophyte (Acremonium coenophialum Morgan‐Jones and Gams) and fescue toxicosis in the 1970's made it possible to achieve high levels of animal performance on low‐endophyte tall fescue. Steer average daily gain (ADG) has been 30 to over 100% higher on low‐endophyte than on high‐endophyte tall fescue pasture. It appears that for each 10% increase in endophyte level there is about 0.1 lb depression in ADG over an entire grazing season. Adverse effects of the endophyte have also been demonstrated in hay and seed. It has been shown to reduce milk production, and there are indications that it adversely affects reproduction. Intake is reduced on endophyte infected fall fescue. Although data are very limited, there are indications that sheep gains are reduced and that horses are afflicted by poor reproduction and agalactia. Much remains to be known about the mechanism of fescue toxicosis, but it is evident that with low‐ or endophyte‐free tall fescue excellent animal performance can be achieved.

loids derived from the endophyte association (Hill et al., 1994), which causes poor weight gain and reproduc-For tall fescue (Festuca arundinacea Schreb.) in the southeastern tion in afflicted animals (Hoveland et al., 1983(Hoveland et al., , 1997 USA, persistence and yield are directly related to infection with a fungal endophyte [Neotyphodium coenophialum (Morgan-Jones & Stuedemann and Thompson, 1993). Ergovaline is con-Gams.) Glenn, Bacon, & Hanlin comb. nov.]. However, most endo-sidered the main ergot alkaloid responsible for most phyte-infected (Eϩ) tall fescue cultivars produce toxic ergot alkaloids animal problems (Lane, 1999). resulting in poor weight gain and reproduction in grazing livestock. Summer drought results in the greatest loss of tall The objective of this paper was to assess the strategy of reinfecting fescue stands in the Southeast, with cultivars infected 'Jesup' and 'Georgia 5' tall fescue with non-ergot alkaloid-producing with their endemic N. coenophialum endophyte demonendophyte strains. Different cultivar-strain combinations were tested strating much better survival in very hot, dry summers against the Eϩ and endophyte-free (EϪ) versions of the same cultivars than the same cultivars with their endophyte removed for stand survival and dry matter yield; in separate experiments, they (Bouton et al., 1993a). Therefore, the toxicity of Eϩ were assessed for toxicity in lambs (Ovis aries ). Most cultivar-strain tall fescue presents livestock producers with a dilemma combinations produced no ergot alkaloids but varied in ability to transmit through seed. The best combination, Jesup (AR542), pos-of whether to grow current Eϩ cultivars for stand persissessed yield and stand survival better (P Ͻ 0.05) than the EϪ checks tence and risk reduced animal performance due to the and equivalent (P Ͻ 0.05) to the Eϩ checks. Lambs gained an average inherent toxins. of 124 g/d on both cultivars containing AR542, which was equivalentAnimal toxicity can be reduced in current Eϩ pasto gains on EϪ forage but approximately 57% greater than gains tures with pasture management such as interplanting on Eϩ forage. Animals consuming forage from EϪ or non-ergotwith clovers to dilute the toxins directly in the forage producing strains did not exhibit depressed serum prolactin or elebefore consumption (Ball, 1997) or controlling of toxicovated body temperatures of animals on Eϩ forage. The strategy of sis directly in the animals with drugs, vaccines, feed reinfecting tall fescue cultivars with naturally occurring, non-ergotadditives, or detoxification agents (Oliver, 1997; Stuedeproducing endophytes appears promising for removing toxicity sympmann and Thompson, 1993). Cultivar improvement to toms and retaining agronomic performance, but intense screening is needed to identify the best cultivar-strain combinations. Program. Received

loids derived from the endophyte association (Hill et al., 1994), which causes poor weight gain and reproduc-For tall fescue (Festuca arundinacea Schreb.) in the southeastern tion in afflicted animals (Hoveland et al., 1983(Hoveland et al., , 1997 USA, persistence and yield are directly related to infection with a fungal endophyte [Neotyphodium coenophialum (Morgan-Jones & Stuedemann and Thompson, 1993). Ergovaline is con-Gams.) Glenn, Bacon, & Hanlin comb. nov.]. However, most endo-sidered the main ergot alkaloid responsible for most phyte-infected (Eϩ) tall fescue cultivars produce toxic ergot alkaloids animal problems (Lane, 1999). resulting in poor weight gain and reproduction in grazing livestock. Summer drought results in the greatest loss of tall The objective of this paper was to assess the strategy of reinfecting fescue stands in the Southeast, with cultivars infected 'Jesup' and 'Georgia 5' tall fescue with non-ergot alkaloid-producing with their endemic N. coenophialum endophyte demonendophyte strains. Different cultivar-strain combinations were tested strating much better survival in very hot, dry summers against the Eϩ and endophyte-free (EϪ) versions of the same cultivars than the same cultivars with their endophyte removed for stand survival and dry matter yield; in separate experiments, they (Bouton et al., 1993a). Therefore, the toxicity of Eϩ were assessed for toxicity in lambs (Ovis aries ). Most cultivar-strain tall fescue presents livestock producers with a dilemma combinations produced no ergot alkaloids but varied in ability to transmit through seed. The best combination, Jesup (AR542), pos-of whether to grow current Eϩ cultivars for stand persissessed yield and stand survival better (P Ͻ 0.05) than the EϪ checks tence and risk reduced animal performance due to the and equivalent (P Ͻ 0.05) to the Eϩ checks. Lambs gained an average inherent toxins. of 124 g/d on both cultivars containing AR542, which was equivalent Animal toxicity can be reduced in current Eϩ pasto gains on EϪ forage but approximately 57% greater than gains tures with pasture management such as interplanting on Eϩ forage. Animals consuming forage from EϪ or non-ergotwith clovers to dilute the toxins directly in the forage producing strains did not exhibit depressed serum prolactin or elebefore consumption (Ball, 1997) or controlling of toxicovated body temperatures of animals on Eϩ forage. The strategy of sis directly in the animals with drugs, vaccines, feed reinfecting tall fescue cultivars with naturally occurring, non-ergotadditives, or detoxification agents (Oliver, 1997; Stuedeproducing endophytes appears promising for removing toxicity sympmann and Thompson, 1993). Cultivar improvement to toms and retaining agronomic performance, but intense screening is needed to identify the best cultivar-strain combinations.