Determination of ergot alkaloid content in tall fescue by near-infrared spectroscopy

Ergot alkaloids are a class of toxic compounds, some of which are produced by a fungal endophyte in tall fescue (Festuca arundinacea Schreb.). The objective of this research was to measure total ergot alkaloid content in tall fescue by near-infrared (NIR) spectroscopy with a calibration developed from immunochemical reference data. Eighty-four tall fescue samples were collected from experiments at the University of Missouri. Samples were from plants that varied in maturity, endophyte status, genotype, growing environment, and storage and preservation treatment. Samples were scanned by NIR radiation and analyzed chemically for ergot alkaloid content using a commercial immunoassay. An empirical prediction equation was developed by regressing NIR reflectance data against absorbance data from the immunoassay. The initial calibrations achieved a 1 - variance ratio (VR) of 0.86 with a mean and standard error of cross validation (SECV) of 0.606 +/- 0.12; however, this was possible only when stockpiled tall fescue samples were omitted from the population. Stockpiled samples were checked for chemical accuracy and spectral similarity to the population, and another set of calibrations was developed. The final calibration, which omitted only those stockpiled samples that were infected with a toxic endophyte, had a 1 - VR of 0.89, with a mean and SECV of 0.682 +/- 0.11. We concluded that total ergot alkaloid content in tall fescue can be quantified by NIR spectroscopy with a calibration developed from immunochemcial data, though it may not be possible to include samples of stockpiled tall fescue if they are infected with a toxic endophyte. Such a calibration can be robust and precise, reliably predicting an entire class of compounds in a diverse population of tall fescue samples.