Microsite conditions influence nutritive value characteristics of a common tall fescue cultivar infected with either a native or a novel non-ergogenic endophyte

Authors: Belesky, David; Ruckle, Joyce; BUSH, L - UNIVERSITY OF KENTUCKY

Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2009
Publication Date: 7/16/2009
Citation: Belesky, D.P., Ruckle, J.M., Bush, L.P. 2009. Microsite conditions influence nutritive value characteristics of a common tall fescue cultivar infected with either a native or a novel non-ergogenic endophyte. Environmental and Experimental Botany. 67:284-292.

Interpretive Summary: Some fungi live entirely within a host plant and can affect the physiology and behavior of grazing livestock that consume the plant – fungus association. The association is very specific, but new technologies have allowed introduction of certain fungal strains into productive tall fescue plant hosts that do not cause detrimental effects in grazing livestock. Fungal infection often benefits productivity and persistence of the host plant, but the influence of novel associations on the nutritive value of the host is unclear. We conducted field experiments to determine how tall fescue allocated resources among plant parts and how this allocation affected the composition of the plant. Plants of the same cultivar, with or without the fungal endophyte, were clipped repeatedly and were grown in either full sun or shade. We found that herbage protein was greater in plants growing in shade than in full sun, but available energy was less in shade-grown compared to plants grown in full sunlight. Accumulation of this readily available carbohydrate might indicate inefficiency in converting products of photosynthesis into plant structure, influencing total production and herbage composition. We tested this idea using a stable carbon isotope index that can indicate plants with high water use efficiency. We found that the index was related to non-structural carbohydrate content of herbage and that it might be useful for identifying shade tolerant forage grasses.

Technical Abstract: Tall fescue [Schenodorus phoenix Holub] often benefits in terms of productivity and persistence when infected with Neotyphodium coenophialum [Morgan-Jones and Gams], Glenn, Bacon, and Hanlin) endophyte. The influence of novel, non-ergogenic endophytes on nutritive value is unclear, especially when simultaneous stresses (e.g., defoliation and shading) are imposed on the host-endophyte association. We conducted a field experiment using container-grown cv. Jesup tall fescue plants with either a native or novel non-ergogenic fungal endophyte (MaxQ™), or devoid of endophyte. Dry matter production efficiency, and nutritive value including crude protein (CP), non-structural carbohydrates (TNC), ergopeptide and pyrrolizidine alkaloids, were determined for plants clipped repeatedly when grown in microsites differing in the amount of available light. Leaf dry matter content was affected by interaction of host-endophyte association with light availability suggesting differences in leaf composition could occur. Herbage CP increased with shading, whereas TNC decreased with increasing shade. Alkaloid concentrations tended to be less in shade-grown plants, and when residual plant height was 5 rather than 10 cm, suggesting that depressed amounts of photosynthate might restrict alkaloid production. Regardless of endophyte infection, undifferentiated phenols concentrations were greater in plants grown in full sunlight compared to shaded sites. Accumulation of TNC could reflect some inefficiency in converting photosynthate to structure arising from limitations (shade, water deficit) associated with environmental conditions. Leaf carbon isotope composition values support this premise with more negative values occurring for shade than full-sunlight grown plants, which suggest this index might be useful for identifying shade tolerant perennial grasses for silvopasture.