Neotyphodium coenophialum mycelial protein and herbage mass effects on ergot alkaloid concentration in tall fescue

Livestock grazing endophyte-infected tall fescue (Festrcca arundinacea Schreb.) pastures often suffer from ergot poisoning. The endophyte, Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin, comb. nov., also provides drought-tolerant, insect-resistant, and disease-resistant qualities to the plant. Therefore, producers are faced with a biological dilemma of risking loss of pasture by using endophyte-free tall fescue pasture or animal losses with endophyte-infected tall fescue pasture. One potential solution is to breed endophyte-infected tall fescue with lower levels of alkaloids. However, breeding could select for plants that are antagonistic to the endophyte, resulting in reduced plant vigor as a consequence of disruption of the mutualistic association between the organisms. The objectives of this study were to determine the relationship between plant mass and endophyte mycelial proteins versus ergot alkaloid concentration. To examine the endophyte effect on mycelial mass, tissue culture regenerants from tall fescue genotype PDN2 were infected with endophyte isolates EDN11, EDN12, and EDN2 to eliminate confounding effects of multiple plant genotypes. Crosses with PDN11 as the maternal parent and plant genotypes DN2, DN12, and DN15 as paternal parents were used to produce a population of different plant genotypes, all containing the same endophyte. Fungal mycelial protein was extracted from lyophilized tall fescue leaf sheath tissue and immunochemically quantified with monoclonal antibodies specific to N. coenophialum proteins. Ergot alkaloid concentration was also immunochemically measured. Quantities of mycelial protein and ergot alkaloids were calculated by regressing experimental values against standards of each. There was no correlation between herbage mass and alkaloid concentration or fungal protein quantity and alkaloid concentration when different fungal isolates were inserted into the same plant genotype. Coefficients of determination (r(2)) were low (0.31 and 0.17) between leaf sheath and leaf blade alkaloid concentrations and endophyte protein when different plant genotypes contained the same endophyte isolate. Likewise, r(2) values were low between leaf sheath and leaf blade alkaloid concentrations and herbage mass. These data suggest that little or no antagonism occurred to the endophyte among plants low in alkaloid concentration.